EPA-600/4-76-001
February 1976
Environmental Monitoring Series
                      DETERMINATION  OF  HEIGHT FOR
                                  STACK  NEAR  BUILDING
                                       Wind Tunnel  Study
                                     Environmental Sciences Research Laboratory
                                         Office of Research and Development
                                         U.S. Environmental Protection Agency
                                   Research Triangle Park, North Carolina  27711

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                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.

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                                        EPA-600/4-76-001
                                        February 1976
DETERMINATION OF HEIGHT FOR STACK NEAR BUILDING

               Wind Tunnel Study
                      by

               William H. Snyder
      Meteorology and Assessment Division
  Environmental Sciences Research Laboratory
     U.S. Environmental Protection Agency
 Research Triangle Park, North Carolina  27711

                      and

             Robert E. Lawson, Jr.
            Northrop Services, Inc.
 Research Triangle Park, North Carolina  27711
     U.S. ENVIRONMENTAL  PROTECTION AGENCY
      OFFICE OF  RESEARCH AND  DEVELOPMENT
  ENVIRONMENTAL  SCIENCES RESEARCH LABORATORY
 RESEARCH TRIANGLE  PARK, NORTH  CAROLINA  27711

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                                DISCLAIMER


This report has been reviewed by the Environmental Sciences Research
Laboratory, U.S.  Environmental Protection Agency, and approved for pub'
lication.   Mention of trade names or commercial products does not con-
stitute endorsement or recommendation for use.

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                                ABSTRACT

Wind tunnel tests were conducted to determine the validity of the "two-
and-one-half-times" rule frequently used to calculate a necessary height
for a stack in the vicinity of a building.  Model stacks and buildings
were placed in a simulated atmospheric boundary layer in a meteorological
wind tunnel.  Smoke was used for flow visualization and methane for
quantitative concentration measurements downwind of the building.  These
studies showed that the two-and-one-half-times rule for the determination
of a necessary stack height in the vicinity of a building is adequate
for a building whose width perpendicular to the wind direction is twice
its height, but that it is unnecessarily conservative for a tall  thin
building.  An alternative rule, called Briggs' alternative, was shown to
be adequate.

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                               INTRODUCTION

A frequently cited and applied "rule of thumb" for the determination of
a necessary height for a stack in the neighborhood of tall  buildings is
the two-and-one-half-times rule.   It says, simply, that a stack must be
at least 2 1/2 times the height of the nearest tall building in order to
avoid downwash of the plume into the wake of the building,  which would
result in relatively high concentrations of pollutants at ground level.
According to Hawkins and Nonhebel (1955), the rule was originally pro-
posed by an English committee in 1932.  It has been amply demonstrated
as adequate from field observations under ordinary circumstances.

The problem is that it is merely a rule of thumb; yet it is frequently
applied across-the-board under unwarranted circumstances.  For example,
in a recently proposed electrical generating plant, which was to use
lignite as a fuel, the plant building was to be 20 m x 30 m and 100 m in
height, for reasons peculiar to the use of lignite.  Application of the
2 1/2 times rule would result in a stack height of 250 m; whereas, in the
absence of building downwash, a 150 m stack would suffice (i.e., an iso-
lated 150 m high stack would result in maximum ground level concentrations
lower than the ambient air quality standards).  This is obviously a very
tall and thin building and is outside the range in which the 2 1/2 times
rule has been adequately verified.  The question is one of considerable
economic importance, since the extra  100 m in stack height would cost on
the order of 10 million dollars.

Briggs  (1973) has proposed an alternative to the 2 1/2 times rule that
may be explained as follows.  Let a be the smaller of either the height
of the building, h, or the maxi.mum width of the building perpendicular
to the wind direction  (generally a diagonal).  Then a necessary and
sufficient stack height is h  =  h +  1.5 a.  This is equivalent to the
2  1/2 times rule for a squat or  cubical building,  but relaxes the 2 1/2
times rule for a tall, slender one.

This study was undertaken with the specific goal of showing that the
2  1/2 times rule does not apply  for the case of a  tall,  thin building.
A more general goal was to find  an alternative method of determining a
necessary and sufficient stack height as a function of the building
aspect ratio  (width to height).  The  study was undertaken in a meteoro-
logical wind tunnel using smoke  for flow visualization and methane as  a
tracer for quantitative concentration measurements.  Although the speci-
fic goal was satisfied, the general goal was not because sufficient time
was not available to study all possible combinations of  building shapes,
distances from stack to building, effluent conditions, etc.  Brigg's  (1973)
rule, however, is shown to be adequate for the case of a.building whose
height is three times its width, and  the 2 1/2 times rule is shown  to  be
necessary for a building whose width  is twice its  height.

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                           SIMILARITY CRITERIA


To ensure that the behavior of the flow in the model  simulates that in
the atmosphere, it is necessary to match certain nondimensional  parameters.
Since this study is concerned only with neutrally stable atmospheric
boundary layers, nonbuoyant effluents, and relatively small  scales; the
Richardson number, Froude number, and Rossby number may be ignored
(Snyder, 1972).  The only remaining parameters of significance are as
follows:

L/h, d/h, hs/h, 6/h, W/U, Uh/v, and Wd/v,

where L = width of building perpendicular to wind direction,
      d = inside diameter of stack at exit,
      h = building height,
      h  = stack height,
      6 = boundary layer thickness,
      U = wind speed at a reference height; for example, at the top of
          the building or stack,
      W = effluent speed,
and   v = kinematic viscosity of air.

The first four of these parameters are easily satisfied by constructing
a  scale model, but since no particular field situation was modeled, d/h
and 6/h, typical of a field situation, were chosen and held constant
throughout the study.  The thickness of the wind tunnel boundary layer
was approximately 2 meters.  On the basis that the thickness of the
neutral atmospheric boundary layer is 300 to 600 m (Davenport, 19613), then
the scale ratio is fixed between 150 and 300.  Thus, a building 30.5 cm
high would correspond to a building in the field 50 to 100 m high, and
a  stack diameter of 0.87 cm would correspond to 1.5 to 3 m in the field.

The remaining two length ratios, the building aspect ratio, L/h, and the
stack height  to building height ratio, h /h, were variables in the experi-
ment.   The goal was to establish rules for downwash as a function of
these variables.

The effluent  to wind speed ratio determines the plume rise for a non-
buoyant plume.  Throughout the study this ratio was maintained approxi-
mately  constant at a nominal value of 2, which is only slightly above
the value necessary to avoid downwash in the wake of the stack.  The rise
of the  plume was negligible in comparison to the stack height or the
building height in all cases.  In fact, the effluent speed was maintained
constant, but the ratio varied because the wind speed at stack top varied
with stack height.  Over the range of stack heights, the wind speed varied
by less than  10 percent.  Thus, the differential plume rise attributable
to the  variation in W/U was miniscule.

The remaining two parameters to be considered are the effluent Reynolds
number  (Ree = Wd/v) and the building Reynolds number  (Re, = Uh/v).  There
is general agreement that precise values for Reynolds numbers are  irrele-

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vant (Snyder, 1972) as long as they are greater than some critical  value
(different in each case).   Plume behavior is independent of the effluent
Reynolds number provided that the effluent flow is fully turbulent at the
stack exit.  The value of 2000 is well-established for the maintenance of
turbulent flow in a pipe.   Lin et al.  (1974) have successfully simulated
buoyant plume rise at a Reynolds number of 530 by tripping the flow, using
an orifice upstream of the stack exit, to ensure a turbulent effluent.
Since the effluent Reynolds number in  this study was 1433, somewhat less
than 2000, a trip consisting of an internally serrated washer placed
10 diameters down from the top of the  stack was used to ensure a fully
turbulent flow at the stack exit.

Concerning the building Reynolds number, Golden (1961) has suggested a
critical Reynolds number of 11,000 for sharp-edged cubical buildings.
Smith (1951) suggested a value of 20,000.  The building Reynolds number
in this study, which was based on the building height and the wind speed
at the top of the building, was 21,500.

The implication of Reynolds number independence is not generally under-
stood.  Townsend  (1956) stated it simply:  "geometrically similar flows
are similar at all sufficiently high Reynolds numbers."  Most nondimen-
sional mean-value functions depend only upon nondimensional space and
time variables and not upon the Reynolds number, provided it is large
enough.  However, two primary exceptions exist:   (1) those functions that
are concerned with the very small-scale structure of the turbulence
(i.e., those responsible for the viscous dissipation of energy), and
(2) the flow very close to the boundary  (the no-slip constraint is a
viscous constraint).  Since full scale winds and buildings (even fairly
light winds and small buildings) result in huge Reynolds numbers, the
full-scale flow is independent of the Reynolds number.  This implies that
the size and shape of the wake behind the building and the nondimensional
turbulence intensities and mean velocity profiles are independent of wind
speed.  Similarly, provided the Reynolds number is large enough, the flow
structure of a model in a wind tunnel  is similar to that of the prototype
and is independent of wind speed.  Hence, the results from the model
apply to all full-scale wind speeds (above the barest minimum).  The flow
structure may change with other variables such as stability of the
atmosphere or different approach flows, and the plume rise will change
with wind speed or buoyancy or effluent speed; but the basic building
wake structure will be independent of wind speed.

In a study designed expressly to corrpare wind tunnel results with full-
scale measurements of building downwash, Barrett, Reed, and Wallen  (1970)
used a model approximately half the present model height and the same
wind speed (hence, approximately half the Reynolds number) and found
reasonably good agreement.  Differences between model and full scale
results were attributed, among other things, to  (1) buoyancy in the  field
plume but not in  the model plume, and  (2) a much  smaller scale of tur-
bulence in the approach flow  (created by a grid)  than is found in the
atmosphere.  Plume buoyancy was not intended to be simulated in the

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present study (effluent momentum was also kept to a minimum),  thus the
results should have a factor of safety already included.   Also,  the scale
and intensity of the turbulence in the present study, as  well  as the more
realistic mean velocity profile in the approach flow, should result in a
more realistic simulation of the field situation.

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                            EXPERIMENTAL DESIGN

The study was undertaken in the meteorological wind tunnel shown in
Figure 1.  The test section is 3.7 m wide, 2.1 m high, and 18.3 m long.
Vortex generators and a castellated barrier similar to those designed
by .Counihan (1969) were used at the entrance to the test section to
create a thick, atmospheric-like boundary layer.  Two-dimensional rough-
ness elements were used to maintain the boundary layer in equilibrium.
They consisted of strips of wood 1.9 cm high by 5.1 cm wide and were
spaced along the floor of the test section perpendicular to the flow
direction on 45.7 cm centers.  This created a boundary layer approxi-
mately 180 cm thick.  The free-stream air speed was 150 cm/sec through-
out all the tests.  A sketch of the boundary layer generation scheme is
shown in Figure 2.

Mean velocity and turbulence intensity surveys were made with a Thermo-
Systems Model 1054A anemometer system using a Model 1210 probe and
0.005 cm hot film sensor.  Signals were fed to a Thermo-Systems Model
1057 signal conditioner and then to a Digital Equipment Corporation
PDP-11 minicomputer.  The nonlinear anemometer signals were digitized
at a rate of 2000 samples per second.  They were then linearized and
further processed digitally on the minicomputer.

Two basic model buildings were constructed.  The tall, thin building
was 10 cm by 10 cm and 30.5 cm tall.  The long building was 10 cm wide,
61 cm long and 30.5 cm tall.  The model stack had an inside diameter of
0.87 cm and a wall thickness of 0.2 cm.  The effluent speed was main-
tained in all tests at 244 cm/sec.  The models were placed at least
4 1/2 vortex-generator heights from the trailing edge of the generator
system.  Separate tests showed the boundary layer to be horizontally
homogeneous from this point onward.

A paraffin oil fog generator (Kenney Engineering Model 1075SG) was used
to produce smoke for the qualitative flow visualization studies.  In
this generator, paraffin oil is aspirated onto a heating element which
creates a fine oil-fog.  A separate, metered air supply then carried the
smoke to the model stack.  Photographs were taken with a Graflex camera
using Polaroid type 55PN film.  The speed of this film is ASA 50.

A 1 percent (10,000 ppm) mixture of methane in air was used as the
effluent and a Beckman Model 400 hydrocarbon analyzer (flame ionization
detector, FID) was used in the continuous sampling mode for the quanti-
tative concentration measurements.  In this mode of operation the FID
has a response time of approximately one second.  The output of the FID
was found, in a separate series of tests, to be linearly proportional to
methane concentration in the range of 1 to 10,000 ppm.

The accuracy of the concentration values depends on quite a number of
factors, including the constancy of the fuel, air, sample, and source
rates, the accuracy of the calibration gases, the stability of the
electronic circuitry, and the averaging time used.  Reproducibility for

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successive samples was found to be within ±5 percent and the absolute
accuracy is thought to be well  within ±10 percent.

Samples were continuously withdrawn from the air stream through a 0.16 cm
diameter tube at a rate of 200  cc/min.   The bulk of the flow bypassed
the FID with 10 cc/min being drawn through the flame.  The output from
the FID was digitized on the PDP-11/40  minicomputer at a rate of 50
samples/sec.  One-minute averages were  found to yield reasonably stable
values of concentration.

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                                 RESULTS

Figure 3 shows the mean velocity and turbulence intensity profiles of
the flow approaching the models.  The mean velocity profile closely
approximates a l/5th-power law that is characteristic of the atmospheric
boundary layer in relatively flat, agricultural-rural country (Daven-
port, 1963).  The turbulence intensity profiles match reasonably well
those observed in the atmosphere by Harris (1968), which are shown for
comparison.

It was necessary to adjust the lighting system (for flow visualization
and photographs) as the stack height or building configuration was
changed.  Since it is possible to bias the photographs (by illuminating
the bottom portion of the plume more than the top portion, for example)
the photographs are presented in pairs.  Photographs in any given pair
were taken under as nearly identical lighting conditions as possible in
order not to bias the results.

Figure 4 shows a comparison of the wake heights p'roduced by the two
buildings.  The wide building produces a considerably higher wake.  The
vertical concentration profiles, shown in Figure 5, show that the wake
of the thin building extends to approximately 1 1/2 building heights;
whereas the wider-building wake extends to 2 building heights.  In
Figure 5 and all subsequent figures showing concentration profiles, the
downstream distance is 3 building heights; the ordinate is the distance
from the ground normalized by the building height, and the abscissa is
the concentration normalized by the concentration of the effluent in-
side the stack.  The shapes of the profiles in Figure 5 are quite
different from one another.

Figure 6 shows the influence of the thin building on the vertical plume
diffusion when the stack height is only 17 percent higher than the
building.  Notice in this and all subsequent photographs that the rise
of the plume above the top of the stack is negligible and that no down-
wash is occurring in the immediate lee of the stack itself.  Figure 7
shows results similar to those in Figure 6 more quantitatively.  The
obvious effects of the building are to (1) lower the mean height of the
plume; (2) decrease the maximum concentration in the plume; (3) increase
the plume width; and (4) skew the concentration distribution toward the
ground.  The ground-level concentration is slight at this point, but it
is apparent that it will increase sharply a short distance downwind.

Figures 8 and 9 show only a minimal influence of the thin building
when the stack height is 33 percent higher than the building.  The only
obvious effect of the building is a slight lowering of the mean plume
height.  Figures 10 and 11 show only a very slight lowering of the
plume when the stack is 50 percent higher than the building.  Figure 12
shows no influence on the plume when the stack is 1 building height
upwind or downwind from the building.

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Figures 13 and 14 show that a stack 50 percent higher than the building
is insufficient to avoid downwash in the case of the wide building.  The
influence of the building is to (1) lower the mean plume height; (2) de-
crease the maximum concentration in the plume; (3) increase the plume
width; and (4) skew the distribution toward the ground.  The ground-level
concentration is quite large and the distribution is fairly uniform with
elevation close to the ground.   Figures 15 and 16 show that a stack
twice the building height is marginally effective in avoiding downwash.
The bottom of the plume has begun to mix in the building wake.  Notice
that the influence of the buildtng has been to raise the mean plume
height slightly.  Finally, Figure 17 shows that the 2 1/2 times rule is
justified for the case of a building whose width is twice its height.

Figures 18, 19, and 20 summarize the effect on the quantitative concen-
tration profiles of varying the ratio h$/fi for the cases of no building,
the thin building, and the wide building, respectively.  The essential
feature of Figure 18 is self-similarity of concentration profiles,  the
only distinct departures being  the vertical separation of the plumes
and the slight differences in peak concentration.   Figures 19 and 20
clearly show the formation of a uniformly mixed layer in the wake of
the buildings, the thin building exhibiting a relatively well-mixed
layer for h /h < 1.17, while for the wide building the mixed layer  ex-
tends to hjh = 1.5.

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                        DISCUSSION AND CONCLUSIONS

The data show that the 2 1/2 times rule is justified for the case of a
squat building whose width perpendicular to the wind direction is twice
its height, but that it is unnecessarily conservative for the case of a
building whose width is smaller than its height.  Application of Briggs1
(1973) proposed alternative to the 2 1/2 times rule for the thin build-
ing would result in a necessary stack height of one-and-one-half times
the building height, which the data from this study show to be adequate.
Although the concentration profiles were measured only 3 building heights
downwind, the photographs show the plume behavior to nearly 6 building
heights downwind, and visual observations confirm all of the above con-
clusions to at least 12 building heights downwind.

Barrett, Reed and Wallen (1970) have concluded from wind tunnel tests
and from field measurements that the 2 1/2 times rule may not be ade-
quate for a very wide building.  Further qualification of the rule will
require additional study.

The conclusions should only be applied, of course, with strict reser-
vations.  Neither the 2 1/2 times rule, nor Briggs1 (1973) proposed
alternative, is adequate in and of itself.  The effluent speed must
exceed one-and-one-half times the wind speed (Sherlock and Lesher, 1954).
The stack must be high enough such that air quality standards would not
be exceeded even in the absence of the building.  Topographical influ-
ences must be treated separately, etc.  The conclusions drawn from this
study may be regarded as having a slight built-in margin of safety in
the sense that the majority of plumes in the field would possess some
buoyancy and a larger effluent momentum, both of which could add con-
siderably to the effective stack height.

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                                REFERENCES

Barrett  C.F., L.E. Reed and S.C. Wallen (1970)  The Use of an Experi-
mental Chimney to Determine the Validity of Wind Tunnel Tests.  Warren
Spring Lab., Stevenage, Herts, England.  Rept. LR123 (AP).  104 p.

Briggs  G.A. (1973)  Diffusion Estimation for Small Emissions.  Air
Resources Atmospheric Turbulence and Diffusion Lab.  National Oceanic
and Atmospheric Administration, Oak Ridge, Tenn.  ATDL Contribution File
No. (Draft) 79.

Counihan  J. (1969)  An Improved Method of Simulating an Atmospheric
Boundary Layer in a Wind Tunnel.  Atmos. Environ. 3_, 197-214.

Davenport  A.G. (1963)  The Relationship of Wind Structure to Wind
Loading. In:  Proceedings of Conference on Wind Effects on Buildings
and Structures (National Physical Lab., Teddington, England, June, 1963)
HMSO, London.  1965.  p. 54-102.

Golden  J.  (1961)  Scale Model Techniques.  M.S. Thesis, College of
Engineering, New York University, New York, New York.  May.

Harris  R.I. (1968)  Measurement of Wind Structure at Heights up to
598 ft. above Ground Level.  Symp. Wind Effects on Buildings and
Structures, Loughborough University of Technology, England.

Hawkins  J.E. and G. Nonhebel  (1955)  Chimneys and Dispersal of Smoke.
J_. Inst. Fuel, 28, 530-545.

Lin  J.T., H.T. Lui, Y.H. Pao, O.K. Lilly, M. Israeli and S.A. Orszag
(1974)  Laboratory and Numerical Simulation of Plume Dispersion in
Stably Stratified Flow over Complex Terrain.  Flow Research, Inc.,
Kent, Wash.  Prepared for U.S. Environmental  Protection Agency, Research
Triangle Park, N.C., under Contract No. 68-02-0800.  Publication
No. EPA-650/4-74-044.  Nov.  70 p.

Sherlock R.H. and E.J. Lesher  (1954)  Role of Chimney Design in Dis-
persion of Waste Gases.  Air Repair.  4_, 13-23.

Smith  E.G. (1951)  The Feasibility of Using Models for Predetermining
Natural Ventilation, Res. Rept., Tex.  Engr. Exp. Stn., 26.

Snyder W.H. (1972)  Similarity Criteria for the Application of Fluid
Models to the Study of Air Pollution Meteorology.  Boundary Layer
Meteorology 3, 113-34.

Townsend  A.A.  (1956)  The Structure of Turbulent Shear Flow.
Cambridge University Press, Cambridge, England.  315 p.

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Figure 1.   EPA Meteorological Wind Tunnel.

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                                                     TEST SECTION
                                                        -18.3m
ro
                                          ROUGHNESS ELEMENTS

                                        VORTEX GENERATORS

                                 CASTELLATED BARRIER
                         Figure 2,   Schematic of vortex generator system.

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I.U
0.9
0.8
0.7
0.6
S0.5
0.4
0.3
0.2
0.1
0
I I I I I
— • MEASURED DATA
__ — 1/5TH ROWER LAW
—
—
—
—
^ — BUILDING HEIGHT
" 1 1 J —4— +•
i i i i ;
L
-
/ "
/ -
/* —
^/ -
--"I i i i
          0.1
                0.2   0.3
0.4    0.5    0.6

    (a)  U/U
0.7   0.8
                  0.9   1.0
N
 1.0

 0.9

 0.8

 0.7

 0.6

 0.5

 0.4

 0.3

 0.2

 0.1

  0
                              [     I
                    T     I      I
                 MEASURED DATA

                 HARRIS (1968)
         BUILDING
          HEIGHT
                                   1-"-k
10    15
20
25
30
35
                         40
                                                           45
                                                                   50
Figure 3.
                                       ,  percent
            Nondimensional vertical  profiles  of (a)  velocity and
            (b) turbulence intensity approaching  building  location.
                                 13

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                         (a)
                         (b)

Figure 4.   Smoke emitted into wakes  of buildings:   (a)  tall,
           narrow building;   (b)  building  same  height but  6
           times as  wide.   (16-sec  continuous exposure  at  f/16)
                               14

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       3.0
       2.5
       2.0
       1.5
       1.0
       0.5
                     \            I

                  •  WIDE BUILDING

                  •  THIN BUILDING
               HEIGHT
     /'   /*
    • • ^»
X\'
vj
                                 I
                    0.1          0.2

                        C/CS,  percent
                         0.3
Figure  5.  Comparison  of concentration  profiles measured 3
          building heights downwind of thin and wide  buildings,
          (Stack height is two-thirds  building height.)
                           15

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                            (a)
                            (b)
Figure 6.   Influence of thin building on  vertical  plume
           diffusion.   (Stack height 1.17 times  building
           height.)  (Eight 1-sec exposures  at  f/16.)
                              16

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              I           I
              x^ = 3.0
              THIN BUILDING
              NO BUILDING
Figure 7.
                          0.3         0.4
                        C/C$ , percent

Influence of thin  building on plume behavior.
1.17 times building  height.)
(Stack  height

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                          (a)
                          (b)

Figure 8.   Influence of thin building on  vertical  plume
           diffusion.   (Stack  height 1.33 times  building
           height.)  (Eight 1-sec exposures  at f/16.)
                             18

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 3.0
  2.5
I             I
x/h = 3.0
THIN BUILDING
NO BUILDING
 2.0(
  1.0
  0:5
   0
    0           0.1          0.2          0.3          0.4
                                      C/CS, percent
Figure 9.  Influence of  thin  building on plume behavior.
           times building  height.)
                                                0.5
0.6
                                          (Stack height  1.3;

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                           (a)
                           (b)

Figure 10.   Influence of thin building on vertical  plume
            diffusion.   (Stack  height 1.5 times building
            height.)  (Eight 1-sec exposures at f/16.)
                            20

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ro
                 3.0
2.5
                                 I             I
                                  x/h = 3.0
                                  THIN BUILDING
                                  NO BUILDING
                 2.0
                 1.0
                 0.5
                   0
                    0
              Figure  11.
                0.1
                                                            I
                                                       1
0.2
  0.3           0.4

C/CS.,  percent
0.5
0.6
          Influence of thin building on plume behavior,  (stack  height 1  5 times
          building height.)

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                             (a)
                             (b)
                             (c)

Figure 12.   Influence of thin  building  on  vertical  plume
            diffusion.   (Stack height is  1.5  times  building
            height;  stack is  one  building  height  (a)  downwind
            and (c)  upwind of building.)   (Eight  1-sec
            exposures at f/16.)

                                 22

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                            (a)
                            (b)

Figure 13.   Influence of wide building on vertical  plume
            diffusion.   (Stack height 1.5 times building
            height.)  (16-sec continuous exposure at f/16.)
                              23

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   3.0
   2.5
   2.0
   1.5
   1.0
   0.5
x/h - 3.0

WIDE BUILDING

NO BUILDING
                                           I
                                    1
                 O/
           0.2
  0.3         0.4
C/C$,  percent
Figure 14.  Influence of wide  building on plume behavior.
            times  building height.)
0.5         0.6
                                          (Stack height 1.5

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                            (a)
                           (b)

Figure 15.   Influence of wide building on vertical  plume
            diffusion.  (Stack height 2 times building height.)
            (16-sec continuous exposure at f/16.)
                            25

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rv>
CTl
                 Ǥ 1.5
                                                                               x/h = 3.0

                                                                               WIDE BUILDING

                                                                               NO BUILDING
                                  0.1
  0.3          0.4

C/C8, percent
0.5
0.6
                   Figure  16.  Influence of wide building on  plume  behavior.   (Stack  height 2 times
                                building height.)

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                              (a)
                                            —.»«»,„,,,
                            (b)

Figure 17.  Influence of wide building on vertical plume
            diffusion.  Stack height 2 1/2 times building
            height.)  (16-sec continuous exposure at f/16.)
                               27

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ro
oo
                    3.0
                    2.5
                    2.0
                  N
                    1.5
                    1.0
                                                                                       = 3.0

                                                                                    h = 30.5 cm
                                                             1
                       0
0.2
  0.3          0.4

C/C$ ,  percent
0.6
                Figure  18.  Effect of  varving  fu/h ratio on  plume concentration  profile for
                             the case o-f no

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ro
10
                     3.0
                     2.5
                     2.0
                     1.0
                     0.5
                                                                           1            I


                                                                                 x/h = 3.0
                                                                           I
                                    0.1
0.2          0.3           0.4


          C/CS j percent
0.5
0.6
                 Figure  19.   Effect 9f  varying h /h ratio  on  plume concentration profile  for
                              thin building.

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CO
O
                             • *    J/*
                       —   /     af 9
                            /*    JT
0.2
                                                          0.3          0.4

                                                            ,  percent
0.5
0.6
                Figure 20,   Effect of varying h  /h  ratio on plume concentration profile
                             for wide  building.

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                                   TECHNICAL REPORT DATA
                            (Please read Instructions on the reverse before completing)
 . REPORT NO.
 EPA-600/4-76-001
                                                            3. RECIPIENT'S ACCESSIOf*NO.
4. TITLE AND SUBTITLE

 DETERMINATION OF HEIGHT FOR  STACK NEAR BUILDING-
 Wind Tunnel  Study
                                                            5. REPORT DATE
                                                           February 1976 (Issuing  Date)
                                                          6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)

 William H.  Snyder* and Robert E.  Lawson, Jr.**
                                                          8. PERFORMING ORGANIZATION REPORT NO.

                                                           Fluid  Modeling Report No.  1
9. PERFORMING ORGANIZATION NAME AND ADDRESS
 Environmental  Sciences Research Laboratory
 Office  of Research and Development
 U.S.  Environmental Protection  Agency
 Research  Triangle Park,  North  Carolina  27711
                                                            10. PROGRAM ELEMENT NO.
                                                            1AA603
                                                          11. CONTRACT/GRANT NO.
 12. SPONSORING AGENCY NAME AND ADDRESS
  Same  as  above
                                                            13. TYPE OF RE PORT AN DPERIOD COVERED
                                                              In-house
                                                          14..SPONSORING AGENCY CODE

                                                            EPA-ORD
 15. SUPPLEMENTARY NOTES
  *0n  assignment from the  National Oceanic  and Atmospheric Administration, U.S.
  Department of Commerce.   **Northrop Services, Inc.
 16. ABSTRACT
  Wind tunnel tests were  conducted to determine the validity  of  the "two-and-one-half-
  times"  rule frequently  used to calculate  a  necessary height for a stack in the
                            Model stacks  and buildings were  placed in a simulated
                                  a meteorological  wind tunnel.   Smoke was used for
  flow visualization and  methane for quantitative  concentration  measurements downwind
  of the  building.  These studies showed that the  two-and-one-half-times rule for the
  determination of a necessary stack height in the vicinity of a building is adequate
  for a building whose width perpendicular  to the  wind direction is twice its height,
  but that it is unnecessarily conservative for a  tall thin building.  An alternative
  rule, called Briggs1 alternative, was  shown to be adequate.
vicinity of a building.
atmospheric  boundary layer in
17.
                                KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
                                              b.lDENTIFIERS/OPEN ENDED TERMS
                                                                        c. COSATI Field/Group
  *Wind tunnel
   Tests
  *Chimneys
  *Height
   Buildings
  *Downwash
   Atmospheric diffusion
                         Boundary  layer
                         Air pollution
Briggs' alternative
14B
13M
20D
 4A
13B
 8. DISTRIBUTION STATEMENT
  RELEASE TO PUBLIC
                                               19. SECURITY CLASS (ThisReport)
                                                     UNCLASSIFIED
                                                                          21. NO. OF PAGES
                                                                               35
                                             20. SECURITY CLASS (Thispage)
                                                   UNCLASSIFIED
                                                                          22. PRICE
EPA Form 2220-1 (9-73)
                                             31
                                                     U. S. GOVERNMENT PRINTING OFFICE: 1976-657-695/5379  Region No. 5-11

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