Environmental Monitoring Series
PLUME DISPERSION IN STABLY STRATIFIED
FLOWS OVER COMPLEX TERRAIN
ise 2
Office if
O.S. Environment)
Research Triangle Part, North Carolina 27711
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped .into five series. These five broad
categories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL MONITORING series.
This series describes research conducted to develop new or improved methods
and instrumentation for the identification and quantification of environmental
pollutants at the lowest conceivably significant concentrations. It also includes
studies to determine the ambient concentrations of pollutants in the environment
and/or the variance of pollutants as a function of time or meteorological factors.
This document is available to the public through the National Technical Informa-
tion Service. Springfield, Virginia 22161.
-------
EPA-600/4-76-022
May 1976
PLUME DISPERSION IN STABLY STRATIFIED FLOWS
OVER COMPLEX TERRAIN
Phase 2
by
H. T. Liu and J. T. Lin
Flow Research, Inc.
Kent, Washington 98031
Contract No. 68-02-1293
Project Officer
William H. Snyder
Meteorology and Assessment Division
Environmental Sciences Research Laboratory
Research Triangle Park, N.C. 27711
ENVIRONMENTAL SCIENCES RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U. S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, N.C. 27711
-------
DISCLAIMER
This report has been reviewed by the Environmental Sciences Research Laboratory, U s<
Environmental Protection Agency, and approved for publication. Approval does not signif
that the contents necessarily reflect the views and policies of the U. S. Environmental
Protection Agency, nor does mention of trade names of cormiercial products constitute en-
dorsement or recommendation for use.
-------
PREFACE
Flow Research has been under contract with the Environmental
Protection Agency (Contract No. 68-02-1293) to continue investigation
of plume dispersion in stably stratified flows over complex terrain. Two
tasks are involved:
Task I - Laboratory simulation of plume dispersion in stably stratified
flows over complex terrain.
Task II - Development of a numerical model using a small-Froude-number
asymptotic expansion to simulate strongly stratified flows over complex
terrain.
The final report consists of two task-oriented parts, each of which
is an individual report. The first is entitled "Plume Dispersion in
Stably Stratified Flows Over Complex Terrain: Phase 2," and the second
is entitled "A Numerical and Experimental Study of Stably Stratified Flow
Around Complex Terrain." In addition, a 16mm color film entitled
"Laboratory Simulation of Stratified Flows Over Complex Terrain," in which
most of the visualization results for both tasks are summarized, is
included as an essential supplement to this final report.
iii
-------
ABSTRACT
Laboratory experiments were conducted in a stratified towing tank
to investigate plume dispersion in stably stratified flows. First, plume
dispersion over an idealized terrain model with simulated elevated inver-
sions was investigated. These results were compared with those of experiments
previously conducted for simulated ground inversions. Second, plume
dispersion in 1-layer stably stratified flows over a realistic terrain
was modeled. The plume dispersion patterns showed a strong interaction
between the stratified flow and the rugged terrain features. The third
experiment was a simulation of plume dispersion during inversion breakup.
Results indicated that pollutants were stirred and carried to the ground
as soon as the convective layer reached the plume that was originally
trapped in the inversion layer.
IV
-------
CONTENTS
Preface iii
Abstract iv
List of Figures vi
List of Tables viii
List of Symbols ix
I. Introduction 1
II. Summary 4
III. Conclusions 5
IV. Laboratory Facilities 8
V. Plume Dispersion in 3-Layer Stratified Flows 19
VI. Plume Dispersion From the Kennecott Smelter Stack .... 29
VII. Plume Dispersion During Inversion Breakup 36
References 46
Appendices
A. The Effect of an Absorptive Layer on Plume Dispersion . . 48
B. The Effect of an Exaggerated Stack on Plume Dispersion . 51
C. The Response of a Hot-Film Probe to a Variation of Fluid
Density 53
-------
LIST OF FIGURES
Number Page
1 A Contour Map of the Idealized Terrain Model ......... 10
2 Terrain Model in the Vicinity of the Kennecott Copper
Smelter in Garfield, Utah 12
3 A Block Diagram of the Effluent Injection Device 14
4 Calibration Curves of a Thermistor Probe 16
5 A Typical 3-Layer Stratification Profile Measured With a
Conductivity Probe in the Towing Tank (Runs Ila and lib) . . 18
6 3-Layer Stratification Structure for the Simulation of
Plume Dispersion Into an Elevated Inversion Layer 20
7 Plume Dispersion Into an Elevated Inversion Layer Over the
Idealized Terrain Model. FQ = 3.08 21
8 Mean Velocity Profile at the Location of the Stack in Run
lib. The Ambient Fluid Was Stratified with a 3-Layer
Structure. The Idealized Terrain Model Was That Described
in Section 5.9 25
9 Dye Visualization of Plume Dispersion From a Stack Located
at the Kennecott Copper Smelter in Garfield, Utah, Under
Stable Conditions. Wind Direction = 315°. F = 2.02 ... 31
10 Mean Velocity Profiles at the Location of the Stack in the
Kennecott Smelter Model. Wind Direction = 315° 34
-------
LIST OF FIGURES (CON'T)
Number
15 Temperature Profiles During the Growth of an Unstable Layer
Adjacent to a Surface in a Stratified Fluid (N = .095 Hz).
The Growth of the Unstable Layer Was Generated by Cooling
the Surface With Dry Ice 45
16 Dye Visualization of Plume Dispersion in a Stratified Flow
Over the Idealized Terrain Model. An Absorptive Layer Was
Installed To Reduce Internal-Wave Reflection. F = 3.11.
See Figs. 17 and 18 in [l] for Comparison 50
vii
-------
LIST OF TABLES
Number Page
1 Summary of Experiments ......... 2
2 Simulation Conditions for the Sharp Inversion
Experiments ....... 11
3 Ground Concentrations Data of the Sharp Inversion
Experiments • 27
4 Simulation Conditions for Plume Dispersion From
the Kennecott Copper Smelter Stack 30
5 Simulation Conditions for the Inversion Breakup
Experiments 38
Vlll
-------
LIST OF SYMBOLS
SYMBOL DESCRIPTION DIMENSION*
B
—
C
C
a
"c
s
D
F
FD
JJ
FH
F,
n
Ffcl
a buoyancy number defined in eq. (B.I)
mean pollutant concentration
ambient pollutant concentration
source pollutant concentration
stack diameter
buoyancy flux of a plume
W
stack Froude number, s
\fe&
V ps
internal Froude number based on the stack
height, °°
NH
internal Froude number based on h, — 7-
' N/z-
internal Froude number based on the Brunt-
_
-2 -2
ML T
_o _7
ML ^T *
-2 -2
ML T
L
L4T-3
_
-
Vaisala frequency at the icn layer,
U
i
_2
g gravitational acceleration LT
H stack height L
h characteristic height, such as that of a
mountain L
K ratio of effluent velocity to free-stream
W
velocity, s
Ucc
L exaggeration factor of the stack diameter
i / ,— _i
Brunt-Vaisala frequency, — /_§_ A£ T
dz
W D
R stack Reynolds number, s
V
R, Reynolds number based on the ridge height,
72 u h
CO —
2 -2
s a stability parameter, (2irN) T
T a time scale defined as the ratio of the
length scale to the velocity scale T
L = length, T = time, T = temperature, M = mass
ix
-------
LIST OF SYMBOLS
SYMBOL DESCRIPTION DIMENSION*
T. time required for the unstable layer to T
reach its maximum height
t time T
U(z) mean velocity component in x direction LT
_i
U free-stream velocity LT
=° ' _1
w vertical velocity component LT
w^ a convective velocity scale LT
W stack effluent velocity LT
s
x.y.z Cartesian coordinate axes in longitudinal,
lateral and vertical directions, respectively L
Z plume trajectory above the stack exit L
Z, elevation of a lower boundary in the towing L
tank
Z final height of the top of a plume in a calm L
environment
Z elevation of an upper boundary in the L
atmosphere
z. the height of the penetrative layer L
i i —3
Ap density difference, |p - p | ML
S a
9 fluctuating temperature T
8 mean temperature T
S mean effluent temperature T
S _o
p density of the ambient fluid at stack exit ML
level
_o
p stack effluent density ML
L = length, T = time, T = temperature, M = mass
-------
SECTION I
INTRODUCTION
The objective of this study is to investigate plume dispersion over
complex terrain in stably stratified flows under several conditions which
might lead to serious pollution episodes. This study is a continuation of
the laboratory investigation of plume dispersion over an idealized terrain
in a 1-layer stratified flow, which simulates a ground inversion (Lin, et
al., 1974 - hereafter referred to as llj ). References to ll are made
frequently to ensure continuity, to provide cross-examination and to
minimize unnecessary duplication.
The present study consists of three (3) subtasks,. which are summarized
in table 1. A brief description of each subtask is given in the following.
The first subtask is the investigation of the plume dispersion over
an idealized terrain model (used in [Ij ) in a 3-layer stratified flow.
The three layers consisted of a neutral layer next to the ground, a neutral
or a stable layer far above the ground, and an extremely stable layer or
inversion layer in between. We then compare the results with those obtained
in III in a 1-layer stratified flow.
Under the second subtask, we conducted experiments of plume dispersion
over a realistic terrain model in a 1-layer stable flow. The realistic
terrain chosen was the Kennecott Copper Smelter vicinity including part of
Great Salt Lake and part of Oquirrh Mountain. The terrain features
are highly rugged and asymmetric, compared to those of the idealized terrain.
We selected one of the existing smelter stacks as the pollutant source in
the experiment. Results are compared with those obtained by Veenhuizen, et
al. (1973), who modeled the same terrain under neutral conditions.
The third subtask is the development of a method which simulates plume
dispersion during inversion breakup. Pollutants once aloft and trapped in
the inversion layer are subsequently mixed and brought to the ground by the
convective motion which develops in the growing unstable layer adjacent to
the ground. Using either mass or heat released from a surface into a
stratified fluid, we conducted several tests in an attempt to simulate the
growth of the unstable layer, and we concluded that heat release provided
a more natural and realistic simulation than mass release.
-------
Table ]. Summary of Uxpev imen t.s
a. Plume Dispersion Experiments
Run Number
la
Ib
] la
fib
I Tic.
Illb
Desc r i pt i on
Simulation of Plume Dispersion
into an F.levated Inversion
S iiiml at ion of P] nine Dispersion
into tin Klevaled inversion
Simulation of Plume Dispersion
into an Ulcvcitocl Inversion
Simulation oi: Plume Dispersion
Into an Klevated In very Jon
Simulation of Plume Dispersion
in Stably Stratified Flows
Over Complex Terrain
Simulation of Plume Dispersion
in Stably Stratified Flows
Over Complex Terrain
Terrain Model
Idealised Terrain Model
(e<|. 3.J)
Idealized Terrain Model
(eq. 3.1)
Idealized Terrain Model
(eq. 3.1)
Ideal i/.ed Terrain Model
(ec,. 3.1)
Kennccott Copper Smelter
(figs. 2 and 9)
Kennecott Copper Smelter
(fijjs. 2 and 9)
Stratification
Profile
*
3-layer (N-S-H)
3-layer (N-S-N)
3-layer (N-S-S)
3-layer (N-S-S)
1-layer (S)
1-layer (S)
K
(..8
3.4
6.8
3.4
2.0
1.0
F,
'(
•", .92, <»
v, 1.85, ™
•», .68, 1.54
«>, 1.37, 3.08
1.04
2.08
Fu
3.08
3.08
3.07
3.07
2.02
2.02
b. Inversion Breakup
-
Desc r i pt ion
Simulation of Plume Dispersion
During Inversion breakup
(Prototype Condi cion-TVA
Paradise Plant 9-13-1966)
Terrain Model
Flat Surface
Stratification
Profile
1-layer (S)
K
°°, 3.76
F,
n
oo, 6.10
FD
3.15
* N = neutral, S = stable
*" Based on tbe stacK height
-------
Section III summarizes the important findings of this investigation
Section IV of this report describes the laboratory facility. Sections V,
VI and VII present, respectively, the results of the three subtasks
described above. The visualization results are also presented in a 16mm
color film entitled "Stably Stratified Flows Over Complex Terrain."
-------
SECTION II
SUMMARY
Laboratory experiments in a stratified towing tank were conducted to
investigate plume dispersion over a complex terrain for various inversion
conditions. The existence of strong vertical shear with alternating over-
shooting and blocked regions characterized the flow field.
For plume dispersion over an idealized terrain model with simulated
elevated inversions, pronounced impingement of pollutants onto the mountain
slopes was observed. In this case, more pollutants were carried around
the model than in previous experiments conducted under weaker ground inver-
sions.
When the idealized model was replaced by a realistic model in a
1-layer stably stratified flow, which was highly rugged and asymmetric,
the dispersion pattern of the latter showed a strong interaction between
the stratified flow and the rugged terrain features. The plume axis of
the latter showed a lateral diversion of 20 from the free-stream wind
direction because of upstream blocking.
Lastly; the feasibility of simulating plume dispersion inversion
breakup was successfully demonstrated by cooling a simulated ground surface
Pollutants were stirred and carried to the ground as soon as the convective
layer reached the plume originally trapped in the inversion layer.
-------
SECTION III
CONCLUSIONS
3.1 Plume Dispersion in 3-Layer Stratified Flows
(i) The bent-over plumes level off and are trapped within the
middle inversion layer. Upstream of the mountain, the
vertical spread of the plume is larger than that in a 1-
layer stable flow as a result of the relatively large
spreading rate in the bottom neutral layer.
(ii) For all the cases, the wind carries the pollutants in the
plume at least partially around the mountain. For the
cases with a more stable middle-inversion layer, most
pollutants are carried around the mountain.
(iii) Direct impingement of pollutants on the mountain slopes
is evident from both visualization results and probe
measurements. For the cases with a less stable middle
layer and a neutral upper layer, the measurement made
on the mountain ridge along the center line of the
model has the maximum concentration. For the cases with
a more stable middle layer, ground concentrations on the
ridge are low because most pollutants are carried around
the mountain.
(iv) For the low internal-Froude-number, F^9, cases, the pollutants
remain aloft both upstream and downstream of the mountain.
The vertical spreads are small. For the high internal-Froude-
number cases, the wind forces pollutants downward as it carries
them around the mountain. Downstream of the mountain,
pollutants appear to be stirred and carried to the ground.
(v) Downslope wind is not as strong as that in a linearly strati-
fied case because the lee wave cannot penetrate into the
bottom neutral layer.
(vi) At the stack location, the velocity profile (Run lib), U(z),
shows a minimum wind-speed region in the middle inversion layer,
where the flow is blocked by the mountain ridge. Pronounced
shear regions are present in the regions near the interfaces of
layers. Strong overshooting occurs in the upper layer.
-------
3.2 Plume Dispersion From the Kennecott Smelter Stack
(i) Under the simulated conditions, the plumes for both cases
(F = 1.04 and 2.08) are quite close to the ground. The
n
vertical and lateral spreads, especially far downstream of
the stack, increases with the internal Froude number.
(ii) For the low internal-Froude-number case (F^ = 1.04), the
plume is aloft throughout the entire length of the model.
The overall plume shape conforms closely with the under-
lying terrain features. When the internal Froude number
increases (F, = 2.08), the thickness of the turbulent
n
boundary layer (TBL) increases to include the plume. As a
result, pollutants are stirred and carried to the ground.
For both cases, however, the ground concentrations are low.
(iii) The wind carries the plumes around Oquirrh Mountain. The
plume was trapped within Little Valley. We observe a 20
initial diversion for both cases. For the high internal-
Froude-number case, the wind forces the plume slightly
farther away from the foothill of Oquirrh Mountain.
(iv) Velocity profiles show that large overshooting occurs at a
level high above the terrain surface and is a result of the
blocking by the tall and massive mountain ridge. The plumes
level off and remain in the blocked region.
3.3 Plume Dispersion During Inversion Breakup
(i) Simulation of inversion breakups have been successfully per-
formed by cooling a model surface using dry ice as the coolant.
The shadowgraph records have shown many interesting features,
such as the developments of the growing domes, the receding
cusps, the sharp interface, etc., which actually occur in
the atmosphere.
(ii) Both the penetration height and the duration of occurrence have
been realistically scaled. The initial penetration height
increases with t1 2, in agreement with other data.
-------
(iii) From the visualization results, we have clearly demonstrated
the capability of simulating the sequential occurrence of
the entrainment of pollutants into the unstable layer.
-------
SECTION IV
LABORATORY FACILITIES
4.1 The Stratified Towing Tank
All experiments, except those concerning inversion breakup, were
conducted in a stratified towing tank, 18.3 m long, 1.2 tn wide and .9m
deep. A detailed description of this facility appears in a previous FRI
report (Pao, et al., 1971). Several features of the towing tank system
which are pertinent to the present investigation are described briefly in
the following: (i) It has a specially-designed filling system, which
facilitates the preparation of a stratified fluid having a predetermined
density profile. (ii) It has transparent side and bottom walls, which
allow visualization experiments from several directions. (ill) It has a
smooth, oil-lubricated carriage, which has a noise level that is approxi-
mately 0.3% of the towing speed. The low noise level permits accurate
measurements of the velocity, temperature and salinity fluctuations with
hot-film probes, thin-film and/or thermistor probes, and single-electrode
conductivity probes. (iv) It has a minicomputer system for direct, on-line,
multiple-channel, data acquisition and subsequent, statistical, data analysis.
In addition, we installed an absorptive layer made of 7-layer nylon
netting on the bottom of the towing tank to reduce internal wave reflection.
The nylon netting is knitted with .12-cm braided threads and has diamond-
shaped openings (1.3 cm x 1.3 cm). The distance between layers was approxi-
mately .6 to 1.2 cm. As an internal wave travels through the absorptive layer,
we observed, from shadowgraph pictures, turbulence generated in the wakes
of the nylon threads. The generation of turbulence, which is finally damped
by the stable stratification, dissipates the energy of the internal wave.
To compare the overall dispersion patterns of two plumes released in a stable
flow, with and without the absorptive layer in place, we conducted several
experiments. The results showed no significant difference between the
corresponding cases (see appendix A).
The inversion breakup experiment took place in a stratified towing
tank, which was 7.3m long, .20 m wide, and .71 m deep. This towing tank
has the same special features as the larger one, except the tracks of the
smaller tank are not oil lubricated.
-------
4.2 Terrain Models
During the experiment, we mounted the terrain models and the stack
upside down on an oil-lubricated carriage in the stratified towing tank.
To simulate a buoyant plume in the atmosphere, we injected a heavy plume
from the inverted stack into the ambient fluid. The plume was traced with
dye, and 35mm still-picture cameras and 16mm movie cameras recorded the
dispersion patterns. We presented the flow visualization results in such
a way that the plume appeared to be injected upward, as in the prototype.
In the sharp inversion experiments (Run la, Ib, Ila and lib), we
used the idealized model described in [ij. Figure 1 shows a contour map of
the model. The characteristic lengths of the model and the stack are
summarized in table 2.
The vicinity of the Kennecott Copper Smelter in Garfield, Utah was
modeled for the experiments of plume dispersion over realistic terrain
under stable conditions. Figure 2 is a topographic map of the area in the
vicinity of the smelter. The stack under investigation is located about
1 km west of Smelter Peak. The surrounding terrain features are extremely
rugged. The terrain model, with a scale of 1/10,000 was designed to
include terrain features for a far-field simulation of the stack plume.
The model covered an area roughly 11 km wide and 30 km long (extending
10 km into Salt Lake in the north and northwest directions, and 11 km in
the south and southeast directions). The modeled area includes Kessler Peak
(elev. 2689 m) and Coon or Farnsworth Peak (elev. 2760 m) of Oquirrh Mountain.
We chose the characteristic height h for the internal Froude number to be
the difference between the elevations of Coon Peak and Salt Lake (elev.
1280 m). The model was 1.1 m wide and 3 m long and simulated a wind
direction of 315°. The model surfaces were intentionally stepped with
vertical steps of .31 cm, corresponding to 30.5-m contour intervals in the
prototype.
4. 3 The Effluent Injection Device
The effluent was a concentrated dye solution (brilliant-blue food dye)
with a predetermined density. The injection device consisted of a heated
flask containing the effluent fluid, a temperature controller (YSI Model 72),
a veristaltic pump (Monostat Model 72-895-05) with insulated Tygon tubing,
-------
X
i
X
ta
CJ
2
<
r-1
CO
c
• Stack and Sraricn for
Velocitv Measurement
O Stations for Surface
Temperature Measurement
60
50
30
10
-10
-30
-50
-6C
i = 13 (cm)
-40 -30 -2Q -10 0 10 20
LATERAL DISTANCE y(cm)
30 40
1—I ^ ^^ T
A Contour Map of the Idealized Terrain Model
1C
-------
Table 2. Simulation Conditions for the
Sharp Inversion Experiments
a. Characteristic Length of the Idealized Terrain Model
Length Scale: 1/2,500
Descriptions
Stack Diameter, D
Stack Height, H
Mountain Peaks Height, h
o
Mountain Peaks Separation
Mountain Ridge Height, h
Prototype [m]
7.94
127.0
609.6
941.0
406.4
Model [cm]
.32
5.08
24.38
37.64
16.26
b. Simulation Conditions
Velocity Scale: 1/100
Run Number
la
Ib
Ha
lib
Uoo[cm/s]
3
6
3
6
-i — '
K
6.8
3.4
6.8
3.4
FD
3.08
3.08
3.07
3.07
Layer
1
2
3
1
2
3
1
2
3
1
2
3
Top of Layer
[cm]
9.7
17.8
40.6
9.7
17.8
40.6
8.6
19.3
55.9
8.6
19.3
55.9
N [HZ]
0
.20
0
0
.20
0
0
.27
.12
0
.27
.12
7h
CO
.92
oo
CO
1.85
OO
CO
.68
1.54
oo
1.37
3.08
-36 pc/lOOml
~5"z~ L J
(prototype)
-.98
6.23
-.98
-.98
6.23
-.98
-.98
12.22
1.59
-.98
12.22
1.59
pg = 1.175
[gm/cm J
11
-------
Smoke Stack
Copper Smelter
Smelter Peak
Thermistor Probes
Fig. 2 Terrain Model in the Vicinity of the Kennecott Copper
Smelter in Garf.ield, Utah.
-------
an accumulator, and a heated hose (Technical Heaters, Inc., Model 352)
connected to the stack. Figure 3 is a block diagram of the device. After
preheating the dye solution to 80°C in the flask, we pumped it through the
stack into the ambient fluid and, just upstream of the stack, reheated the
effluent in the heated hose, which maintained the temperature at 90 + 2°C.
Fine temperature control was essential since thermistor probes measured the
temperature at the terrain surface downstream of the stack to indicate
ground concentration. Prior to each experiment, we calibrated the effluent
discharge rate with a stopwatch and a graduated cylinder.
To ensure a turbulent plume at the stack exit, we installed a sapphire
nozzle ranging from .13 mm to .38 mm in diameter about .5 cm upstream of the
stack exit. The size of the nozzle is dependent upon the flow rate and the
stack diameter. As the effluent passed through the nozzle, it expanded to
the designed size at the stack exit. At a constant discharge rate, the
stack Reynolds number is inversely proportional to the nozzle diameter.
4.4 Instrumentation
Two, 10-channel, constant-temperature anemometers (Models 1051-10
and 1053-B, Thermo Systems, Inc.) using fourteen (14) conical and cylindrical
hot-film sensors (TSI Models 1230S and 1290 AK) measured the mean and fluctu-
ating velocities of the approaching flow near the stack. The sensors were
insulated with two coats of quartz for use in conductive fluid. The system
has a frequency response of up to 1 kHz. Hot-film sensors mounted on a
strut measured the vertical velocity profiles. These sensors covered a
vertical distance of 30 cm, and the spacing decreased between sensors toward
the terrain surface. We calibrated the sensors either before or after each
velocity measurement with the strut lowered to a distance (the model was
upside down) at which no sensors were within the turbulent boundary of the
terrain model. For the extreme cases (Runs Ila and lib), the maximum
specific gravity change was about .03 and the corresponding corrections
required for the sensor were -8% and +6% for the mean and fluctuating
measurements, respectively (appendix C). Five towing speeds were used for
the calibration, and the data points were least-squares fitted with second-
degree polynominals.
The plumes used in the study were basically turbulent although they
tended to relaminarize far downstream of the stack under extremely stable
13
-------
Temperature
Controller
(YSI Model 72)
Preheated Dye
Solution
(80°C)
Veristaltic Pump
(Manostat Model
72-895-05)
Ceramic Stack
Heated Hose
(Technical Heaters,
Inc., Model 352)
90°C
Accumulator
Fig. 3 A Block Diagram of the Effluent Injection Device
-------
conditions. In a turbulent flow, the ratio of the turbulent diffusivity of
salinity to that of heat is approximately unity. Therefore, the temperature
concentration measured in the model can be directly extrapolated to the
field (see eq. (4.1)). Using the temperature as a tracer, we measured
ground concentrations with the thermistor probes (Fenwal Electronics
GC32SM2). The thermistor probes have a nominal resistance of 2000 ft and a
temperature coefficient of -3.4%/°C at room temperature. The probe tip is
0.76 mm in diameter, and the time constant (3db point) of the thermistor
probes in still water is about .07 sec. A 10-channel gauge with the
thermistor probe as one arm of the wheatstone bridge measured the temperature
of the fluid. The sensitivity of the system is typically 10 volt/ C. The
output of the gauge went directly into the minicomputer system for on-line
calibration and data acquisition. Signal conditioners increase the overall
sensitivity of the temperature gauge to 30 volt/ C with a noise level
equivalent to 1.4 x 10 C, and the thermistor probe has long-term stabil-
ity (a typical drift of .01 C/year). The probes are pre-calibrated against
a precision thermometer with .01 C divisions (Brooklyn Thermometer Company,
Inc.) in a constant-temperature bath, which is equipped with a temperature
controller (YSI Model 72) of .01 C repeatability. In the range of tempera-
ture differences of interest (0~.5 C), the calibration curves appear to be
quite linear. We used second-degree polynominals to best fit the calibration
data. Before each experiment, we measured a reference temperature in the
towing tank and 'fed it into the computer. The computer shifted the recorded
calibration curve so that is was parallel to the pre-calibrated curve.
Figure 4 is two typical calibration curves of the thermistor probes. For
ground concentration measurements, we installed the probes in the terrain
model with the probe tips exposed to the ambient fluid at a distance
approximately .2 cm above the terrain surface. We then measured and recorded
the coordinates of the probes, in reference to the stack. When extrapolated
to the field, the following analogy can be made
o-ea
0-0
s a
m
C - C
a
"c - "c
s a
(4.1)
JP
15
-------
-9
20. 'J
TEMri.'IRATUUb'. ( C)
a. liiyh Gain
-1
-3
-7
I I
j I
8 10 12 14 16
°
TEMPERATURE (C)
b. Low Gain
Pig. 4 Calibration Curves of a Thermistor Probe
-------
where C is the mean pollutant concentration, C is the ambient concen-
_ a
tration and C is the source concentration.
A conductivity gauge (Model 1110) developed by Flow Research, Inc.,
measured the density profiles in the tank. This gauge has a frequency
response of from DC to 1 kHz. The sensor was a single-electrode conduc-
tivity probe, which has a .025-mm stainless-steel tip platinized with
platinum black solution. The sensitivity of the conductivity gauge is about
3
1 volt per 0.025 gm/cm . The probe was calibrated in jars of salt solution
of known density, and the calibration data were least-squares fitted with
a second-degree polynominal. Figure 5 shows a 3-layer stratification profile
measured with a conductivity probe in the towing tank.
17
-------
Terrain Surface
Mountain Ridqe
Mountain Peaks
70
1.00
1.05
SPECIFIC GRAVITY
ig. 3 A Typical 3-Layer Stratification Profile Measu^^cl Wi^h
a Conductivity Probe in the Towing Tank (Runs Ila and lib)
13
-------
SECTION V
PLUME DISPERSION IN 3-LAYER STRATIFIED FLOWS
For the experiments, a 3-layer stratified fluid was prepared in
the towing tank to simulate an elevated inversion layer in the atmosphere.
Figure 6 shows two sketches of the structure of the 3-layer fluid. Figure
5 corresponds to the actual density profile of fig. 6b (upside down model).
The 3-layer fluid consists of a neutral layer (constant density) adjacent
to the ground, a neutral (fig. 6a) or a stable (fig. 6b) layer high above
the ground layer, and an extremely stable or inversion layer between the
two. Figure 6 also shows the reference elevations of the idealized
terrain model and of the stack. We purposely arranged the top of the
middle inversion layer at a level above the mountain ridge so the plume
would not rise above the mountain.
In the experiment, we conducted two (2) runs for each of the two 3--
layer stratified cases (fig. 6). Table 2 lists the experimental conditions
for all four (4) runs. The free-stream wind speed is denoted by U , and
the ratio of the effluent speed W to U is denoted by K. The stack Froude
number, F , is defined as F = W / ^/gDAp/p , where D is the stack diameter,
D D S S
Ap is the difference in the densities of the effluent and the ambient fluids
at the stack exit, g is the gravitational acceleration and p is the effluent
S
density. The internal Froude number, F, ., is defined as F, . = U^/N./j, where
F, . = U^/N.Tz, N. is the Brunt-Vaisala frequency of the i layer, and h is
the height of the mountain ridge.
5.1 Flow Visualization
Figure 7 shows the side and plan views of the plumes in 3-layer
stratified flows over the idealized terrain model. The side views (figs.
7a through 7d) indicate that the overall dispersion patterns resemble, to
some degree, those observed in 1-layer stratified flows (figs. 15 through
18 in [ij), especially in the region upstream of the mountain.
In the near field, the turbulent motion in the plume dominates the
plume dispersion. The plumes released into the bottom neutral layer rise
into the middle inversion layer. Overshooting of the plumes, in the in-
version layer for the low internal Froude number (figs. 7a and 7c) is evident
19
-------
W, = 20.4 cm/s
F0= 308
Mountain Peaks
Mountain -tidge
Layer 3. N, = 0 Hz
(Neutral)
Layer 2. N; - 2 Hz
(inversion)
Layer 1 N, = 0 Hz
(Neutral)
r-30 cm
r-20
a. Runs la and Ib
cm/sec
Mountain Peaks
Mounta.n
= 3.07
Layer 3. N,= .12 Hz
(Stable)
Layer 2, N, - .27 Hz
(inversion)
Layer 1. N, = O H
(Neutral)
30 cm
h20
b. Runs Ila and lib
3-Layer Stratification Structure for the Simulation
of plume Dispersion Into an Elevated Inversion Layer
20
-------
. 5 m
a. Run la, U^ = 3 cm/s, K = 6.8, F = .92
I
b. Run Ib, U^ = 6 cm/s, K = 3.4,
1.85
c. Run Ha, U = 3 cm/s, K = 6.8, F
d. Run lib, U = 6 cm/s, K = 3.4, F,0 = 1.37
Fig. 7 Plume Dispersion Into an Elevated Inversion Layer Over
the Idealized Terrain Model. F = 3.08
21
-------
e. Run la, UOT = 3 cm/s, K = 6.8, F
f. Run Ib, U^ = 6 cm/s, K = 3.4, F, „ = 1.85
g. Run Ha, Uro = 3 cm/s, K = 6.8, F, = . 68
h. Run lib, U = 6 cm/s, K = 3.4, F, . = 1.37
Fig. 7 (Cont'd) Plume Dispersion Into an Elevated Inversion
Layer Over the Idealized Terrain Model. F = 3.08
22
-------
The bent-over plumes level off and are trapped within the inversion layer.
The vertical spreads of the leveling plumes increase with an increase in
internal Froude number, F^. Compared with the corresponding cases in [l],
the vertical and lateral spreads of all the present cases are quite large
as a result of the relatively large spreading rate in the bottom neutral
layer.
Farther downstream, the mountain blocks the flows in the inversion
layers. For all the cases, the pollutants in the plumes are carried by
the wind, at least partially, around the mountain. Direct impingement of
the plume onto the mountain slope is evident. For the low internal-Froude-
number cases (figs. 7a and 7c), the plumes are aloft upstream and down-
stream of the mountain. The wind carries the pollutants around the mountain
at the same level as those upstream and downstream of the mountain. This
phenomenon implies that the vertical displacements of the streamlines around
the mountain are small. When the internal Froude numbers are doubled (figs.
7b and 7d), the wind forces the pollutants carried around the mountains
downward to the ground. This complicated dispersion pattern apparently
results from the interaction of the stratified flow with the terrain and
from the vertical pressure gradient developed as the fluid flows around
the mountain slope (see Task II report). Downstream of the mountain,
the pollutants which were once aloft at small Froude numbers, are stirred
intensively until they reach the ground. As a result, we expect high
concentrations on the ground. The tops of the pollutant layer do not
show significant differences in the elevation upstream and downstream
of the mountain, as opposed to the cases observed in figs. 16 and 18 in
[ ll . In the present experiment, lee waves cannot penetrate into the
bottom neutral layer; and, therefore, the strength of the downslope wind
(the descending portion of a lee wave) which tends to carry the pollutants
toward the ground, decreases considerably.
Figures 7e through 7h show the plan views of the plumes. The plumes
released from the stacks (right) were advected toward the mountain. The
I-shaped, white portion shown in fig. 7h corresponds to the peaks and the
ridge between the peaks (see, also, fig. 1). For all cases, the plan views
(figs. 7e through 7h) show that the wind carries the plumes, at least partially,
around the mountain. For the cases with a less stable inversion layer (figs.
23
-------
7e and 7f), the plumes are carried over and around the mountain while, for
the cases with a more stable inversion layer (figs. 7g and 7h), the plumes
are carried mainly around the mountain. This result demonstrates that the
plume rise decreases while the upstream blocking increases with increasing
stability. Comparing the individual cases with the same stratification
profile, we find the initial lateral spread decreases while the plume rise
increases with an increasing internal Froude number, F^ (fig- 7e vs. 7f
and 7g vs. 7h).
The two cases with a more stable, middle inversion layer (figs. 7g
and 7h) are strikingly different. For the low internal-Froude-number case,
the valley just downstream of the mountain ridge is practically free of
pollutants (fig. 7g). The pollutants, which are carried by the wind around
the mountain, are transported downstream along the outside contour of the
mountain. On the other hand, for the high internal-Froude-number case (fig.
7h), the valley is filled with pollutants. In this case, a strong reverse
flow, which carries pollutants from the sides into the valley, appears to
develop in the lee of the mountain. A small portion of the pollutants
trapped in the downstream valley is contributable to those carried over the
mountain ridge (see, also, the movie).
5.2 The Velocity Profile
Hot-film probes on the x-z plane at the stack location measured the
mean velocity profile, U(z), of Run lib. Figure 8 shows these measurements.
A dotted line in fig. 8 denotes the free-stream wind or towing speed, U .
The profile shows several interesting features, which are the consequences
of the interaction between the stratified flow and the topography. The
wind speed in the middle inversion layer, where the flow is blocked by the
mountain ridge (upstream blocking), appears to be at a minimum. In the
bottom neutral layer, the velocity is higher than that in the middle layer
because upstream blocking does not occur in a neutrally stable flow. In the
upper stable layer, where no major obstacle blocks the flow, we measured
strong overshooting from the mean wind or towing speed. Overshooting is
an established characteristic of stably stratified flows (Long, 1959 and
Pao, 1968). The profile displays several regions of high vertical shear.
The most pronounced shear region occurs just above the mountain ridge, between
24
-------
Ei
o
N
O
H
C-H
>
P
w
50
40
30
20
10
Muntaxn Peaks
Mounbain
Ridqe
Stack Exit
N3=.12 Hz
U(cm/s)
Pig. 8 Mean Velocity Profile at the Location of the Stack in Run
lib. The Ambient Fluid Was Stratified With a 3-Layer
Structure. The Idealized Terrain Model Was That Described
in Section 5.9
-------
the blocked and the overshooting regions. The visualization results (fig. 7)
show that the plume levels off at an elevation slightly below that of the
mountain ridge, where the flow is noticeably blocked.
5.3 Concentration Measurements
Ten (10) thermistor probes that were installed in the terrain model
measured the ground concentration on the mountain slope. Their positions
are indicated on the contour map shown in fig. 1. Table 3 summarizes the
results of Runs la, Ib, Ila and lib.
For Run la where F7 9 = .92, the wind carries the plume over and around
the mountain, and maximum ground concentrations occur on the top of the
mountain ridge between the peaks (probes nos. 1 and 3) and have values as
high as 4,400 ppm relative to the effluent concentration. High ground con-
centrations were also present at other locations on the mountain slope
(probes nos. 4, 5, 9 and 10) at the level where a portion of the pollutants
in the plume are carried around the mountain. These measurements further
support the observation (Lin, et al., 1974) that direct impingement of a
plume onto a mountain slope occurs under stable conditions. The maximum
root-mean-square concentration occurred on the mountain ridge (probe no.
3). This location corresponds to that of the plume edge, where the con-
centration signal is highly intermittent.
When the internal Froude number increases (Run Ib, F, = 1.85), the
plume rise tends to increase slightly, and the ground concentrations on
the mountain ridge decrease considerably. The measurement of the highest
concentration still occurred at probe no. 1.
In Run Ila, the wind carries the pollutants around the mountain (fig.
7a), and ground concentrations on the ridge are low. The vertical spread is
so limited that the plume is not in direct contact with any of the probes.
When the internal Froude number increases (Run lib, F7„ = 1.37), the
plume rise increases, and a small portion of the pollutants are carried over
the mountain ridge. As a result, measurement of concentrations on the ridge
were slightly higher (probe no. 1). The vertical spread also increases and
high concentrations were measured at other locations on the mountain slope
(probes nos. 2, 4, 7 and 10).
26
-------
Table 3. Ground Concentrations Data of the Sharp Inversion Experiments
Thermistor
1
2
3
4
5
6
7
8
9
10
x [cm]
61.00
57.47
61.00
57.47
67.00
64.77
36.83
38.74
44.45
57.47
y lcml
0.00
0.00
6.35
6.35
0.00
0.00
19.69
19.69
19.69
13.97
z [cm]
16.26
8.89
16.50
11.68
12.95
14.48
10.29
12.09
14.10
13.97
Ambient Conditions
Run Number
la
ePc]
20.75
20.37
20.62
20.44
20.65
20.37
20.35
20.37
20.48
20.42
20.35
(6-6 )/(6 -9 )
a s a
5.74 x 10~3
2.87 x 10~4
3.87 x 10~3
1.29 x 10~3
4.31 x 10~3
2.87 x 10~4
0.0
2.87 x 10~4
1.87 x 10~3
1.01 x 10~3
-
J7 PC]
3.82 x 10~2
1.36 x 10~3
1.04 x 10"1
4.44 x 10~2
1.39 x 10~2
5.89 x 10~3
_2
1.07 x 10
2.82 x 10~2
8.06 x 10~2
2.31 x 10~2
1.0 x 10~3
Ib
Q [°c]
20.56
20.42
20.36
20.45
20.44
20.41
20.28
20.33
20.38
20.32
20.28
(e-ea)/(es-ea)
4.02 x io~3
2.01 x 10~3
1.15 x 10~3
2.44 x 10~3
2.29 x 10"3
1.86 x 10"3
0.0
7.17 x 10"4
1.43 x 10"4
5.74 x 10"4
-
J7[°d
2.71 x 10~2
2.32 x 10~2
4.72 x 10~2
5.04 x 10"2
3.69 x 10~2
3.62 x 10~4
2
1.12 x 10
4.83 x 10"2
5.21 x 10~2
1.69 x 10~2
3.0 x 10~4
Effluent Temperature 9 = 90 + 2 C
S
-------
Table 3. (Cont'd) Ground Concentrations Data of the
Sharp Inversion Experiments
Thermistor
Probe No.
1
2
3
4
5
6
7
8
9
10
x [cm]
61.00
57.47
61.00
57.47
67.00
64.77
36.83
38.74
44.45
57.47
Y [cm]
0.00
0.00
6.35
6.35
0.00
0.00
19.69
19.69
19.69
13.97
z [cm]
16.26
8.89
16.50
11.68
12.95
14.48
10.29
12.09
14.10
13.97
Ambient Conditions
Run Number
Ila
e L°c]
19.93
19.91
19.92
19.90
19.91
19.92
19.91
19.91
19.92
20.01
19.90
(6-6 )/(6 -6 )
a s a
4.28 x 10~4
1.43 x 10~4
2.85 x 10~4
0.0
1.43 x 10"4
2.85 x 10~4
-4
1.43 x 10
1.43 x 10~4
2.85 x 10~5
-3
1.57 x 10 J
-
Je2 [°c]
2.65 x 10~3
1.70 x 10~3
4.42 x 10~3
4.30 x 10~3
2.02 x 10"3
1.01 x 10~3
-3
3.82 x 10
2.13 x 10~3
4.80 x 10~3
-3
5.57 x 10
1.0 x 10~3
lib
¥ [°c]
20.00
20.12
19.95
20.29
19.96
19.93
20.20
19.93
19.92
20.05
19.90
(6-6 )/(8 -6 )
a s a
1.43 x 10~3
3.14 x 10~3
7.13 x 10~3
5.56 x 10~3
8.56 x 10"4
4.28 x 10~4
T
4.28 x 10
4.28 x 10"4
3.14 x 10"4
0
2.14 x 10
-
>2 PC]
7.46 x 10~2
5.12 x 10~2
8.92 x 10~3
6.93 x 10~3
3.51 x 10~2
2.32 x 10~3
i
1.17 x 10
9.42 x 10"3
6.36 x 10~3
T
2.14 x 10
1.0 x 10"3
Effluent Temperature 6 = 90 + 2 C
-------
SECTION VI
PLUME DISPERSION FROM THE KENNECOTT SMELTER STACK
To simulate plume dispersion in 1-layer stratified flows over a
realistic terrain, we selected one of the stacks at the Kennecott Copper
Smelter in Garfield, Utah and the surrounding terrain. Table 4 summarizes
the simulation conditions for both the prototype and the model.
The terrain model, whose features are more rugged and asymmetric than
the idealized model, had a scale of 1/10,000. To ensure a turbulent plume,
we enlarged the stack diameter by a factor of two (1/5,000 scale). According
to the discussion in appendix B, the effect of the diameter exaggeration on
plume dispersion in the far field is insignificant under given neutral or
stable conditions, as long as the buoyancy number in the model remains
the same as that in the prototype. The buoyancy number in the exaggerated
stack was preserved by reduction of the speed ratio, K, by 21% (see appendix
B).
6.1 Flow Visualization
Figure 9 show plumes in stably stratified flows (1-layer) over the
rugged terrain model southeast of the Kennecott Copper Smelter in Garfield,
Utah. The plumes in both cases (Run Ilia and Illb), with F, = 1.04 and 2.08,
respectively, are quite close to the ground. The vertical and lateral spreads
of the plumes, although quite different in the two cases, are small compared
to the vertical and horizontal extents of the area modeled.
For the low internal-Froude-number case (fig. 9a) , where F, = 1.04,
the overall shape of the plume conforms closely to the underlying terrain
features. The plume is aloft over the entire length of the model. Far
downstream of the stack, the plume tends to relaminarize. This relam-
inarization indicates that the turbulence intensity at the plume level,
although quite close to the ground, is low and the turbulent boundary layer
(TBL) is very thin.
When the internal Froude number increases by a factor of two (fig. 9c)
and F =2.08, the overall shape of the plume tends to smoothen out. The
vertical and lateral spreads increase considerably, and the wind carries the
pollutants in the plume downward to the ground. No tendency of relaminarization
29
-------
Table 4. Simulation Conditions for Plume Dispersion From
the Kennecott Copper Smelter Stack
a. Characteristic Length
Length Scale: 1/10,000
Description
Stack Diameter, D
Stack Height, H
Elevation of Coon Peak
Characteristic Height, h
Prototype [m]
8.23
124
2,760
1,480
Model [cm]
*
.17
12.4
27.6
14.8
Enlarged by a factor of two
Simulation Conditions
Description
Free-Stream Wind Speed, U^ [m/s]
Effluent Speed, Ws [m/s]
Brunt-Vaisala Frequency, N [Hz]
Internal Froude Number, F,
' n
Speed Ratio, K
Stack Froude Number, F
Lapse Rate, - -^ [°C/100m]
Ambient Temperature, 9 \_ CJ
3.
Effluent Temperature, 6 [°cj
r s -,
3
Effluent Density, p gin/cm
Prototype
Run Ilia
6.1
15.24
.004
1.04
2.5
2.11
.78
0
177
—
Run I lib
12.2
15.24
.004
2.08
1.25
2.11
.78
0
177
—
Model
Run Ilia
.02
.04
.13
1.04
2.0
2.02
—
20.6
90
1.035
Run I lib
.04
.04
.13
2.08
1.0
2.02
—
20.6
90
1.035
30
-------
5km
a. Run Ilia, Side View, U = 2 cm/s, K = 2.0, F, = 1.04
Mean Wi-nd
b. Run Ilia, Plan View, U = 2 cm/s, K = 2.0, F - 1.04
5 km,
c. Run Illb, Side View, U = 4 cm/s, K = 1.0, F, = 2.08
Mean Wind
d. Run IIlc, Plan View, U^ = 4 cm/s, K = 1.0, F, = 2.08
Fig. 9 Dye Visualization of Plume Dispersion From a Stack
Located at the Kennecott Copper Smelter in Garfield,
Utah, Under Stable Conditions. Wind Direction = 315°,
F = 2.02
31
-------
of the plume is observable, and the plume edges are relatively ill-defined.
This phenomenon indicates that the thickness of the TBL has increased to
include the plume and that the turbulence intensity at the plume level
increases.
The importance of terrain effects on plume dispersion in stably strati-
fied flows are unambiguously demonstrated by the plan views of the plumes
(figs. 9b and 9d). The wind definitely carries the plumes around Oquirrh
Mountain and diverts it into Little Valley, which is northeast of the
mountain. In the near field, the terrain effects are so dominant that the
initial diversion (—20° from the free-stream wind direction) of the plume
is independent of the internal Froude number. For both cases, the plumes
are carried into Little Valley avoiding the steep mountain slope on the
southwest of Oquirrh Mountain, For the low internal-Froude-number flow,
F7 = 1.04, the wind seems to carry the plume into the valley along the
foothill of Oquirrh Mountain. Farther downstream, in the lee of the
mountain, the plume tends to turn back to follow the mean wind. When the
internal Froude number is double, the plume is carried slightly farther
away from the mountain toward the northeast.
In the near field, the lateral plume spread of the high internal-
Froude-number case is slightly smaller than that of the low internal-Froude-
number case. This reduction is present because the turbulent motion in the
plume dominates the plume dispersion. In the experiment, we increased
the internal Froude number for the same stratification by increasing the
towing speed. The plume in the low internal-Froude-number case, therefore,
has a relatively long time to spread before the wind advects it to a
fixed downstream location. As the plume is advected farther downstream,
however, the role of the background turbulence becomes increasingly
important. In the far field, the lateral plume spread in the high
internal-Froude-number case becomes considerably larger than that in
the low internal-Froude-number case because the turbulence intensity
at the plume level is higher in the former than that in the latter.
Under neutral conditions, a plume rises considerably higher with a
larger vertical spread and a much smaller lateral diversion than under stable
conditions (Veenhuizen, et al., 1973). These distinctive differences are
not surprising because the vertical motion in a neutral flow is not inhibited
32
-------
and because the buoyant plume tends to rise above rather than around the
mountain. The large lateral diversion observed in the stable cases is the
result of upstream blocking, which does not occur in the neutral cases. The
generation and maintenance of a thick TBL with high turbulence intensity
further disperses the plume as the neutral fluid flows over the rugged
terrain.
6.2 Probe Measurements
6.2.1 Velocity Profiles
Figure 10 shows the mean velocity profiles, U(z), of Runs Ilia and
Illb, which we measured with hot-film probes at the stack location. The
dotted lines denote the free-stream speed for the respective runs. Both
profiles show blocked regions at low levels and overshooting regions high
above the blocked regions. The abnormally large overshooting from the
mean wind speed is the result of blocking induced by the tall and massive
mountain ridge on the southwest of the smelter. This ridge includes
Kessler Peak (elev. 2689 m) and Coon Peak (elev. 2760 m) of Oquirrh
Mountain. From the visualization results, the plumes were released in
and appear to remain in the blocked regions.
6.2.2 Concentration Measurements
Based on the visualization results, locations were selected to
install ten (10) thermistor probes for the measurement of ground concen-
trations (see fig. 2). The probes were installed to cover an area large
enough that the distribution of ground concentrations could be inferred from
the data. The background concentrations were measured with probes installed
outside the plumes.
For both Runs Ilia and Illb, the results show no appreciable ground
concentrations at any of the locations inside and outside the plumes. The
measured temperatures were all comparable with the thermal noise level
(.01°C) in the towing tank. If a source S02 concentration of 2000 ppm is
assumed, the noise level of .01°C is equivalent to a full-scale noise level
of .28 ppm, which is lower than the Federal Secondary Ambient Air Quality
Standard of .5 ppm (3-hr average). In the experiment, the sampling time
was about 60 seconds, which is equivalent to a sampling time of 1/2 hour in
the full-scale case (time scale = 1/33). Note that the experiment was
designed to simulate a steady wind condition.
33
-------
e
o
o
H
e-<
K
W
0
U (cm/s)
10 Mean Velocity Profiles at the Location of the Stack
in the Kennecott Smelter Model.
315°
Wind Direction =
-------
From the visualization results, we expect the ground concentrations
in Run Ilia to be low because the plume is aloft throughout the entire length
of the model. In Run Illb, however, pollutants in the plume appear to be
stirred and carried to the ground. Apparently, the turbulent motion enhances
the plume spread, and the pollutants have been diluted greatly.
35
-------
SECTION VII
PLUME DISPERSION DURING INVERSION BREAKUP
After a nocturnal inversion is formed, a plume released into the stable
layer is transported downwind in the form of a flat ribbon with variable
lateral spreading and minimum vertical dispersion. Subsequently, as the
result of surface heating, a growing unstable layer below replaces the
nocturnal inversion. As the thermally induced vertical mixing develops and
builds to include the plume, pollutants in the plume are entrained into the
unstable layer and are uniformly stirred and carried to the ground. Thomas,
et al. (1970) measured maximum ground concentrations in a narrow band along
the plume axis during the inversion breakup period. The unsteady, convective
motion, also termed penetrative convection, has been the subject of some
full-scale study (Lenschow and Johnson, 1968 and Thomas, et al., 1970)
and of some theoretical modeling (Lilly, 1968). In the laboratory, Deardorff,
et al. (1969) investigated the penetrative convection in a tank filled with
thermally stratified distilled water. Subsequently, Willis and Deardorff
(1974) conducted experiments to study the rate of dispersion of nonbuoyant
particulates released from a near-ground source into the convective layer.
In this study, we attempted to develop a method of simulating the
penetrative convection in the atmosphere by releasing either heat or mass
from a surface to initiate and to maintain the growth of the unstable layer
adjacent to the ground. Pollutants are released from a stack to alloxv in-
vestigation of the dispersion characteristics during the unsteady inversion-
breakup period. For realistic simulation of the unsteady inversion-breakup
phenomena, several conditions, in addition to those described in [I I must be
satisfied. Geometric similarity requires that the maximum height of the
unstable layer, z., be simulated correctly, i.e.,
m
(7.1)
where the subscripts m and p refer to the model and the prototype, respectively,
Kinematic similarity requires
U
c<
W,
U
cc
W,
(7.2)
m
36
-------
where w^ is a convective velocity scale (Deardorff and Willis, 1975). In
the present study, however, we made no attempt to satisfy eq. (7.2).
When simulating any unsteady phenomena, one must define the
characteristic time scale, T, which is the ratio of the length scale
to the velocity scale. Correct simulation of the unsteady inversion-
breakup phenomenon requires
IT I
(7.3)
where T± is the time required for the unstable layer to reach its
maximum height.
We conducted several tests to develop a method to simulate inversion
breakup. First, we generated the growth of the unstable layer adjacent to
a surface by allowing a heavy salt solution to infiltrate slowly through
the surface (an upside-down model). Although we could easily control the
penetration height by varying the density of the salt solution, the observed
convective motion lacked the large-scale components (the growing "dome" as
described by Deardorff, et al., 1969) observed in the field. These large-
scale components are responsible for the fumigation of a plume in an
unstable layer. Second, we used ice in an attempt to generate the convective
motion, but because the heat flux was not sufficiently large (the
stable fluid was at a temperature of 20 C), the penetration height was too
small to include the plume. Finally, we tested dry ice and obtained satis-
factory results.
A special device was designed by FRI to facilitate the experiment.
First, we filled two aluminum channels (6.1 m x 7.6 cm x .32 cm) with dry
ice and then placed them into the towing tank. The bottom of the channels
were in direct contact with the water surface. Between the channels was
a gap of 1.3 cm, through which we would tow the stack to simulate plume
dispersion in a crosswind.
The field conditions at the TVA Paradise Power Plant on 13 September
1966 (Thomas, et al. , 1970) were simulated at FRI in this experiment. Two
183-m stacks are located in the Paradise Plant, but only one of them was
in operation on that day. Table 5 lists all the experimental and the
37
-------
Table 5. Simulation Conditions for the
Inversion Breakup Experiments
a. Characteristic Length
Length Scale: 1/5000
Description
Prototype [mj
(TVA Paradise Power Plant)
Model [cm]
Stack Diameter, D
Stack Height, H
7.92
183
.158
3.66
b. Simulation Conditions
Description
Free-Stream Wind Speed, U [m/sl
Effluent Speed, Ws [m/s]
Ambient Temperature, 6 [ Cj
a
Stack Effluent Temperature, 0 1 Cj
5
Lapse Rate Before Breakup, - -^ [°C/100m]
Lapse Rate After Breakup, - ^- [°C/'100m]
Brunt-Vaisala Frequency Before Breakup, N [HZ]
Effluent Density, p gm/cm
Ambient Fluid Density, p gm/cm
3. 1— -J
Internal Froude Number, F
Stack Froude Number, F
iJ
Speed Ratio, K
Prototype
(TVA Paradise Power
Plant 9/13/1966)
0, 4.88
18.0
20.6
144
-1.2
.98
.0043
;;;
0, 6.20
3.15
», 3.69
Model
0, .020
.075
23.0
23.0
.09
1.043
1.005
0, 6.10
3.15
00 , 3.76
38
-------
simulated prototype conditions. Figure 11 shows the actual and idealized
profiles of the temperature soundings before and after the inversion breakup
The atmosphere adjacent to the ground was stably stratified and was nearly
isothermal at 0658. It finally became neutrally stratified (adiabatic) at
0934. The terrain surrounding the plant site is relatively flat, as shown
on the USGS topography map. The terrain effect on the plume released from
the 183-m stack under stable conditions will probably be insignificant
except very close to the ground. Field observations of the Keystone plume
(Schiermeier and Niemeyer, 1968 - figs. 11 and 12), where the terrain
features appear to be more rugged than those of the Paradise plant, have
substantiated, at least qualitatively, the above statement. For a
feasibility study of the simulation of the inversion breakup, representa-
tion of the surrounding terrain by a flat surface is therefore sufficient.
7.1 Flow Visualization
To visualize the structure of the growing unstable layer, we used
the shadowgraph method described in III. Figure 12 is a plot of the
penetration height z.(t). The average of z. was measured from shadowgraph
pictures. The initial slope of the data indicates that z. is proportional
1/2 1
to t before the convection stablizes, which agrees with the observation
of Turner (1968). In the present experiment, we cooled the fluid by a
constant temperature rather than by a constant heat flux. This cooling
process explains the leveling off of the curve at large times, as the
temperature in the fluid approaches that of the cooling surface. The time
required for z. to reach its maximum of 10.5 cm ( 1700 m in the prototype)
is about 8 minutes (3 hours in the prototype), which is in the same range as
the simulated conditions given in table 5 and fig. 11.
Figure 13 is a series of shadowgraph pictures which show the growth
of the unstable layer with time. A plume released into the calm (no cross-
wind), stable layer is also shown in each picture.
The interface between the unstable and stable layer is distinctive,
but irregular, as shown in fig. 13. Frequently, individual thermals with
well-defined boundaries form and rise into the stable layer. The larger
the size of the thermal, the higher it rises. Penetration of large
thermals into the stable layer occurs frequently and randomly at the
interface. The frontal boundaries of these large thermals in the
39
-------
900 -
300 •-
7 0 0 ' ~
500
500
O 400
H
E-
300
DJ
200
100--
Paradise ?o
9-13-196
Time
.- 0653
+- 0934
Adiabatic
I-.To? of
Stack
/\
«/er Plant
1C
20
15 10
Before
Breakup
15
TEMPERA'
a. Actual Profiles
:URS(°C)
After
Breakup
:o
25
b. Idealized Profiles
Fig. 11 Typical and Idealized Temperature Profiles for the
Inversion Breakuo Experiment (see Thoruas, et al.,
1970)
-------
10 -
e
u
•H 5
M
U
M
EH
&
H
O
EH
M
O
M
H
ffi
I I
I 1 l i
10
100
500
1000
TIME t(sec)
Fig. 12 Penetration Height z.(t) of an Unstable Layer Generated by Cooling a Surface
With Dry Ice in a Stratified Fluid (N ~.1 Hz)
-------
t =r 90 s
t = 120 s
t = 200 s
t = 270 s
Fig. 13 Shadowgraph Pictures of Entrainment of Pollutants in a
Growing Unstable Layer During Inversion Breakup
U = 0, N = .09 Hz, K = 0°, Fu = 0, Fn = 3.15
00 JJ
-------
stable layer take the shape of a dome (Deardorff, et al., 1969).
Individual domes always overshoot the interface and then subsequently
recede. The repetition of the overshooting and receding motions of
the large thermals appear to contribute efficiently to the growth of
the unstable layer. Between domes, cusp-shaped regions, through which
the undisturbed fluid is entrained into the unstable layer, are observed.
The intensity and frequency of the generation of large thermals decrease
with time. A sharp and relatively smooth interface develops as the
penetrative motion becomes less vigorous. The sharp interface observed
in the shadowgraph pictures corresponds to the "super" stable region
measured by Deardorff, et al. (1969).
When simulating a crosswind, we towed the stack as soon as we
secured the channels filled with dry ice. Figure 14 is a series of
pictures, in sequence, which show, by tagging the same patch of pollutants
in the plume (the camera was stationary to the towing tank), the evolution
of the entrainment process. Before the unstable layer builds to reach the
plume levels, pollutants in the plume remain aloft. As soon as the top
of the growing unstable layer reaches the plume level, pollutants begin
to become entrained in the unstable layer (fumigation). As the convective
motion continues to penetrate the stable layer, it stirs the entrained
pollutants within the unstable layer, and a well-mixed layer adjacent to
the ground is finally established.
7.2 Temperature Profile During Inversion Breakup
Ten (10) thermistor probes mounted on a strut measured the temperature
profile, 6(z,t), adjacent to the surface (the bottom of the channels) where
the growth of the unstable layer began. The gain of the thermistor gauge
was modified to cover a temperature range of 25 C. Figure lib shows a
typical calibration curve of a thermistor probe.
The vertical temperature profiles, 6(z,t), adjacent to the ground
are plotted in fig. 15. The temperature profiles tend to stablize in about
10 minutes, which is slightly longer than the time required for z± to reach
its maximum (fig. 12). The initial cooling at t-tQ = 0 is the result of
radiation which came from the bottom of channels before they were secured
in place. Note that a kink on the temperature profile at z ^ 3 cm tends
to develop after t-tQ exceeds 600 seconds.
43
-------
0
I
1 km
2 .
1
t = 4 0 s
t = 300 s
z .
i
t = 400 s
t = 720 s
Fig. 14 Dye Visualization of the Sequential Entrainment
of Pollutants (Fumigation) in a Growing Unstable
Layer During Inversion Breakup. The Pictures Were
Taken With the Camera Stationary to the Towing Tank
(Following the Same "Patch" of the Plume)
44
-------
30
0
2
O
W
25
20
15
10
Symbols
O
*
x
a
•
v
-2
t-t [sec]
o L J
0 +
50
200
400
600
1000
1400
4 6 3 10 12 14 16 13 20 22
TEMPERATURE(°C)
Fig. 15 Temperature Profiles During the Growth of an Unstable
Laver Adjacent to a Surface in a Stratified Fluid
(>f= .095 Hz). The Growth of the Unstable Layer '--7as
Generated by Cooling the Surface With Dry Ice.
-------
REFERENCES
Briggs, G. A. (1969) Plume Rise, U.S. Atomic Energy Commission Critical
Review Series, TID-25072.
Deardorff, J. W. and Willis, G. E. (1975) "A Parameterization of Diffusion
into the Mixed Layer," Manuscript No. 0201-75-9 (to be published in
JAM), National Center for Atmospheric Research, Boulder, Colorado.
Deardorff, J. W., Willis, G. E. and Lilly, D. K. (1969) "Laboratory
Investigation of Non-Steady Penetrative Convection," J. Fluid Mech.
3J5, 7-32.
Defant, A. (1961) Physical Oceanography, vol. 1, Pergamon Press, New York.
Ippen, A. T. (1966) Estuary and Coastline Hydrodynamics, McGraw-Hill,
New York.
Lenschow, D. H. and Johnson, W. B. (1968) "Concurrent Airplane and Balloon
Measurement of Atmospheric Boundary-Layer Structure Over a Forest,"
J_. Appl.' Meteor. 1_, 79-89.
Lilly, D. K. (1968) "Models of Cloud-Topped Convection Layer Under a Strong
Inversion," Quart. J. R. Meteor. Soc. 94, 292-309.
Lin, J. T., Liu, H. T., Pao, Y. H., Lilly, D. K., Israeli, M. and Orszag,
S. A. (1974) "Laboratory and Numerical Simulation of Plume Dispersion
in Stably Stratified Flow Over Complex Terrain," Report No. EPA 650/4-
74-044, USEPA, Research Triangle Park, North Carolina.
Liu, H. T., Lin, J. T., Pao, Y. H., Veenhuizen, S. D., Peecher, D. W. and
Hiatt, G. L. (1974) "The Plume Dispersion in Stably Stratified Flow
Over a Flat Plate and a Three-Dimensional Terrain," Flow Research
Film No. 6.
Long, R. R. (1959) "The Motion of Fluids With Density Stratification,"
J. Geophys. Res. _64_, 2151-2163.
Martin, S. (1966) "The Slow Motion of a Finite Flat Plate Through a Viscous
Stratified Fluid," Tech. Report No. 21 (ONR Series), The Johns Hopkins
University.
Pao, Y. H. (1968) "Laminar Flow of a Stably Stratified Fluid Past a Flat
Plate," J. Fluid Mech. _34_, 795-808.
Pao, Y. H., Lin, J. T., Carlson, R. L. and Smithmeyer, L. P. C. (1971)
"The Design and Construction of a Stratified Towing Tank With an
Oil-Lubricated Carriage," Flow Research Report No. 4 (APL/JHU
POR-3530).
Sanborn, V. A. (1972) Resistance Temperature Transducers. Metrology Press
Fort Collins, Colorado. '
46
-------
REFERENCES (CONT'D)
Schiermeier, F. A. and Niemeyer, L. E. (1968) "Large Power Plant Effluent
Study," (LAPPES), Vol. 1 - Instrumentation, Procedures, and Data
Tabulations, National Air Pollution Control Administration Publication
No. APTD70-2.
Thomas, F. W., Carpenter, S. B. , Leavitt, J. M. , Montgomery, T. L., Colbaugh,
W. C. (1970) "Report on Full-Scale Study of Inversion Breakup at Large
Power Plants," Tennessee Valley Authority, Div. of Environ. Research
and Development, Muscle Shoals, Alabama.
Turner, J. S. (1968) "The Behavior of a Stable Salinity Gradient Heated
From Below," J. Fluid Mech. 33>, 182-200.
Veenhuizen, S. D. , Lin, J.-T., Pao, Y.-H., Peecher, D. W. and Hiatt, G. L.
(1973) "Laboratory Simulation of Plumes From Kennecott Copper Smelters
in Garfield, Utah: Neutral Atmosphere," Flow Research Report No. 9.
Willis, G. E. and Deardorff, J. W. (1974) "A Laboratory Model of the Unstable
Planetary Boundary Layer," J. Atmos. Sci. 31, 1297-1307.
Wunsch, C. (1969) "Progressive Internal Waves on Slopes," J. Fluid Mech.
35, 131-144.
47
-------
APPENDIX A. THE EFFECT OF AN ABSORPTIVE LAYER ON PLUME DISPERSION
In the atmosphere, the upper boundary is nonreflective. Internal
waves generated near the ground propagate upward and finally disperse and
dissipate into the upper atmosphere. Partial reflection is possible,
however, if the outgoing waves encounter sharp inversion layers. In general,
we can write the upper boundary condition in the atmosphere as
3w
3z
0, (A.D
where w is the vertical fluid velocity and Z is the elevation of the upper
boundary considered. In a stratified towing tank, the bottom of the tank
imposes a reflective upper boundary condition (since the model is upside
down), i.e.,
Is =0, (A.2)
Z = Zb
where Z is the elevation of the tank bottom in reference to the terrain-
b
model surface.
The reflective boundary condition might cause the formation of un-
realistically strong downstream blocking and prevent full penetration of
downslope winds toward the leeward surface of the mountain. To resolve
this speculation, one could install an absorption layer on the bottom of
the towing tank to absorb, at least partially, the internal energy generated
by the towed terrain model. We could then observe, with the absorptive
layer in place, whether the flow pattern would be more asymmetric and the
pollutants would be carried further toward the ground and into the turbulent
boundary layer in the lee of the mountain. Absorbers of various types have
been applied in the laboratory to reduce reflection of surface and internal
waves from tank walls, by Ippen (1966) and Wunsch (1969). The present
experiment, however, requires revisions to design an absorptive layer
for effectively reducing the reflection of internal waves from the
bottom of the towing tank.
48
-------
Figure 16 shows two plumes in a 1-layer stratified flow over the
idealized terrain model. In this experiment, we installed an absorptive
layer made with nylon nettings (section 5.1) on the bottom of the towing
tank to reduce internal wave reflection. Other experimental conditions
were the same as those shown in figs. 17 and 18 in III. For the overall
dispersion pattern, we observed no significant difference between the
corresponding figures, with or without the absorptive layer in place. The
direct interaction between the stratified flow and the terrain is so
strong, especially close to the terrain surface where plume dispersion is
heavily influenced, that the effect of the reflection from the solid bottom
becomes insignificant.
49
-------
5 m
a. Side View, U^ = 3 cm/s, K = 6.8, F, = 1.37
b. Side View, UOT = 6 cm/s, K = 3.4, F, =2.
73
. 5 m
c. Plan View, UOT = 6 cm/s, K = 3.4, F, = 2.73
Fig. 16 Dye Visualization of Plume Dispersion in a Stratified
Flow Over the Idealized Terrain Model. An Absorptive
Layer Was Installed To Reduce Internal-Wave Reflection.
FD •• 3.11. See Figs. 17 and 18 in [l] for Comparison.
50
-------
APPENDIX B. THE EFFECT OF AN EXAGGERATED STACK ON PLUME DISPERSION
Under neutral conditions, the application of a stack with an exaggerated
diameter in simulated plume dispersion has been investigated by Veenhuizen,
et al, (1973). The main advantage of this approach is that the flow field is
not distorted or disturbed. In the following, we attempt to examine the
possible errors involved with the use of an exaggerated stack.
Let a buoyancy number be defined as
"
B -
/Z\ _ B x 2 /D\/x
U) -
where D is the stack diameter, F is the buoyancy flux of the plume, H is
the stack height, F is the stack Froude number, K is the speed ratio, U
is the ambient wind speed (assumed to be uniform), and p and p are the
a s
ambient fluid and effluent density, respectively. By using eq. (B.I), we
can rewrite the second equation on p. 33 in Briggs (1969) in a dimensionless
form as
3 - 'x\2
,HJ - 4\par WW (B-2)
where Z is the plume trajectory above the stack exit. In the near field
when x/H is small, both terms on the right-hand side (r.h.s) of eq. (B.2)
are significant. In the far field, where the ratio of the stack diameter
to the stack height, D/H is small, we can neglect the second term on the
r.h.s of eq. (B.2) except for the very large speed ratio, K. Under neutral
conditions, the speed ratio, K, is of order 1. Therefore, if we consider
the plume dispersion in the far field, the plume rise depends only on the
buoyancy number, B, defined in eq. (B.I).
Under stable conditions, the final height of the tops of plumes Zfc
under calm and stable conditions with a constant density gradient is given
by Briggs (1969) as
5F1/4 s- . (B.3)
Using eq. (B.I) with s = (2irN)2, we can rewrite eq. (B.3) as
= 1.26B174 F3/4 . (B.4)
51
-------
Equation (B.3) or (B.5) is also applicable to cases with a light crosswind
(Lin, et al., 1974). With the presence of a crosswind, an empirical
formula for predicting the final rise of a bent-over plume is also given
by Briggs (1969) as
Z = 4.0 (F/Us)1/3 . (B.5)
Again, with the use of eq. (B.I), eq. (B.5) can be rewritten as
-^ = 1.17B173 F^'3 . (B.6)
Equations (B.2), (B.4) and (B.6) all show that the plume rise in the far field
is preserved under a given stable condition, i.e., when F is constant,
as long as the buoyancy number, B, is identical for the model and the proto-
type.
Consider plume dispersion experiments which use an exaggerated stack.
According to eq. (B.I), there are two ways to preserve the buoyancy number,
B. One can reduce the speed ratio (K~L ) if F remains unchanged, or
1/3
if K remains unchanged, one can increase the stack Froude number (F ~ L
where L is the exaggeration factor of the stack diameter). For example,
when we exaggerate the stack diameter by a factor of two, i.e., L = 2,
then we can preserve B, by reducing K by 21% or by increasing F by 21%.
The optimum choice, however, depends on which regime of the plume we wish to
investigate. In the near field, the ratio K is more significant while, in
the far field, the stack Froude number is the more important factor.
52
-------
APPENDIX C. THE RESPONSE OF A HOT-FILM PROBE TO A VARIATION OF FLUID DENSITY
During the calibration of the hot-film probes, the probe strut was
lowered about 30 cm to avoid disturbance from the terrain surface. As a
result, the probes encountered fluids of different densities during measure-
ment and calibration. In the following, the response of the hot-film probes
to the variation of fluid density is examined, and the required correction
is evaluated.
Consider an extreme case when a hot-film probe is used to measure the
velocity at a level where the fluid density, p, =1.01 and then is cali-
brated at a different level where p = 1.04. Neglecting the heat loss to
the supports, the rate of production of Joulean heat Q attributable to
the current I = E/R is equal to the heat loss to the surrounding fluid,
that is,
E2/R = hTTD£(T - T), (C.I)
w w
where E is the supply voltage, R is the film resistance, h is the
w
heat transfer coefficient, D is the diameter of the cylindrical hot-film
probe, £ is the length of the sensor, T is the film temperature and
T is the ambient fluid temperature.
Equation (C.I) can be written to include the Nusselt number N = -r- ,
U K,
where k is the thermal conductivity, as
E2 = TTD£R (T - T)kN . (C.2)
w w u
Note that only k and Nu in the right-hand side of eq. (C.I) depend on
the fluid density. After differentiation and normalization, the sensitivity
of the hot-film output to density is
f - k (f + £) • (c'3)
\ '
According to King's relation (Sandborn, 1972), we have
N = .318 + .69 \/Re , (C.4)
u
where Re = — is the Reynolds number. The respective kinematic viscos-
ities for p = 1.01 and p = 1.04 are (Martin, 1966)
v| = .00953 and vl . _, = -00990 cm /sec.
'p = 1.01 'p = 1.04
53
-------
For U = 6 cm/sec and D = .002 in., the Nusselt numbers are
Nu|p = 1>Q1 = 1.552 and Nu p= ^^ = 1.529.
The thermal conductivity for p = 1.01 and p = 1.04 are (Defant, 1961)
k|p = 1.01 1-355 x 10 and k|p = 1.04 1>3 X Q
(cal/cm sec C)
Substituting the above values in eq. (3), we have
^ = | (-.023 - .015}
Ap = .03
= -.02.
According to King's law, the velocity-voltage relation is
E2 ~ U5. (C.5)
Therefore, the corresponding correction for the mean velocity is
- -.08. (C.6)
As a reference, the experimental error is approximately 10% for mean velocity
measurements.
The turbulent velocity is proportional to the local slope of the E-U
curve, i.e.,
dE
u~dU '
AE
The correction for u, by using eq. (C.5) and the value of — .
E Ap — .Uj
is, therefore,
u /dE\
for the extreme case considered.
A/dE\
Au -dU^ _3 (M)= +.
06
54
-------
TECHNICAL REPORT DATA
(Please read instructions on the reverse before completing)
1. REPORT NO.
EPA-6QQ/4-7fi-n??
3, RECIPIENT'S ACCESSIOIVNO.
i ITLE AND SUBTITLE
PLUME DISPERSION IN STABLY STRATIFIED FLOWS OVER
/"" /"*i I j r*» f \i -w ^ _. _ . — .,
COMPLEX TERRAIN
Phase 2
5. REPORT DATE
May 1976
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
H. T. Liu and J. T. Lin
8. PERFORMING ORGANIZATION REPORT \O.
Flow Research Report No. 57
9. PERFORMING ORGANIZATION NAME ANO ADDRESS
Flow Research, Inc.
1819 South Central Avenue
Kent, Washington 98031
10. PROGRAM ELEMENT NO.
1AA009
11. CONTRACT/GRANT NO.
68-02-1293
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Sciences Research Laboratory
Office of Research and Development
U. S. Environmental Protection Agency
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final Reoort. 5/74-.V75
14. SPONSORING AGENCY CODE
EPA - ORD
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Laboratory experiments were conducted in a stratified towing tank to
investigate plume dispersion in stably stratified flows. First, plume dispersion
over an idealized terrain model with a simulated elevated inversion in the
atmosphere was investigated. These results were compared with those of experiments
previously conducted under simulated ground inversions. Second, plume dispersion
in 1-layer stably stratified flows over a realistic terrain was also modeled. The
plume dispersion patterns showed a strong interaction between the stratified flow
and the rugged terrain features. Third, plume dispersion during inversion breakup
was simulated. Results indicated that as soon as the convective layer built to
reach the plume, pollutants were stirred and carried to the ground.
17.
KEY WORDS ANO DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENOE3 TERMS
:OSATI Field/Group
*Tests
*Plumes
*Atmospheric diffusion
*Stratification
*Terrain
Air pollution
148
21B
04A
14G
08 F
136
13. DISTRIBUTION STATEMEN"
RELEASE TO PUBLIC
UNCLASSIFIED
66
20. SECURITY CLASS ,'This page/
UNCLASSIFIED
22. PRICE
SPA Form 2220-1 (9-73)
55
------- |