Wind flow Energy and Simulation
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THESIS RESEARCH AND PROGRAMMING
IN POST PROFESSIONAL PROGRAM
MASTER OF ARCHITECTURE DEGREE
SCHOOL OF ARCHITECTURE AND PLANNING
UNIVERSITY OF COLORADO AT DENVER
NATURAL VENTILATION: Wind flow Energy and Simulation
RESENTED BY: ALI MAHMOUD MALKAWI
VDVISOR : Prof. SOONTORN BOONYATIKARN
Prof. ROBERT W. KINDIG
Prof. PHILLIP GALLEGOS
VCADEMIC YEAR: SPRING, 1990
Approved by School of Architecture and Planning, University of Colorado at Denver in partial fulfillment of the
equirements for Thesis Research and Programming.
(Prof. Soontom Boonyatikam, D. Arch.)
This work has been done with the help of Professor Soontom Boonyatikam, the director of the
Technology Lab at the School of Architecture and Planning at the University of Colorado at Denver
tnd strong encouragement of Professor Robert W. Kindig, the Professor Emeritus in the School of
Architecture and Planning at the University of Colorado at Denver. Deep thanks to Professor
3hillip Gallegos the committee member. Appreciation goes to Seung-Bok Leigh, doctoral
:andidate at the University of Michigan and also to Scott R. Spiezle, from NTPI, and to my
:olleague Chen Hwai for his help and constructive comments.
The need for man to reduce thermal stress on his body has caused the development of several
means of controlling his environment. The industrial revolution of the 19th century brought about
the use of gas and electricity. In the 20th century, the need to conserve our energy is of great
importance. We are rediscovering the natural means of ventilation used by previous generations.
Ventilation is needed for both comfort and health. Fresh air is constantly required to replace stale,
contaminated air naturally produced by man. Air movement across the skin causes a cooling effect.
Among the ways to achieve this comfort goal has been the use of electric fan power, mechanical
means, and systems using expensive equipment.
To utilize our energy more efficiently, we must begin to utilize natural systems to provide
ventilation. These include the natural forces of wind caused by convection, and thermal
stratification the rising of warm air in relation to cooler air. Many factors are involved in the
success of natural ventilation in a building. A correct relationship must be established between
these factors, which include: wind speed, wind direction, air temperature, building design,
dimension, and location of the building and configuration of the building site and the location of
interior objects blocking wind flow.
Experimental and theoretical approaches are required to create the correct relationship between
these factors. This study will focus on the effects of natural ventilation of cooling the buildings and
discuss wind flow characteristics and application from an energy point of view. The study also
discuss the tools used for simulating the wind in terms of types, characteristics and the basic
requirements for simulation for wind tunnels and in more details for Fluid Mapping Technique
characteristics and application.
TABLE OF CONTENTS
LIST OF FIGURES.........................................................................iv
I. NATURAL VENTILATION...........................................................1
Ventilation and Thermal Loads..............................................4
Flow Caused by Wind.......................................................12
Flow Caused By Thermal Forces.............................................13
Natural Ventilation Due to Both Effects...................................14
Effect of Height on Wind Speed............................................14
II. WIND TUNNELS.................................................................16
Types of Wind Tunnels.....................................................16
Basic Requirements for the Simulation.....................................20
III. FLUID MAPPING TECHNIQUES....................................................24
Physical Configuration of a Fluid Mapping Table...........................25
A comparison Between the Fluid Mapping Table and The wind Tunnel..........21
LIST OF FIGURES
1.1 Schematic Diagram of the Bioclimatic Chart........................................................2
1.2 Relationship Between Wind Speed, Air Temperature and Comfort When Strolling, Calculated for Four
Clothing Conditions in both Sun and Shade.......................................................3
1.3 Design Strategies Based on Climatic Conditions by Givoni ( Stein, 1986 )..........................7
1.4 Mean Pressure Coefficients on the Wall of a Low-Rise Building (Holmesl986).......................10
1.5 Variation of Wall Average Pressure Coefficients for a Low-rise Building (Swami and Chandra 1987).10
1.6 Pressure Coefficients on the Roof of a Low-rise Building (Holmes 1986)...........................11
1.7 Average Roof Pressure Coefficients for a Tall Building...........................................11
1.8 Pressure Differences Caused by Stack Effect for a Typical Structure (Heating)....................12
1.9 Increase in Flow Caused by Excess of One Opening Over Another....................................14
1.10 Typical Mean Wind Speed Profiles Over Different Terrain Roughness................................15
2.1 Meteorological Wind Tunnel, Fluid Dynamics and Diffusion Laboratory, Colorado State University...17
2.2 Industrial Aerodynamics Wind Tunnel, Fluid Dynamics and Diffusion Laboratory, Colorado State
2.3 Environmental Wind Tunnel, Fluid Dynamics and Diffusion Laboratory, Colorado State University....19
3.1 Configuration of Fluid Mapping Table.............................................................25
3.2 Long Shadow Effect...............................................................................26
3.3 Delay Action of the Flow Line....................................................................26
3.4 Identify the Wind Shadow Zone....................................................................21
3.5 Different Pressure Zones Around Building.........................................................27
3.6 Configuration of Wind Tunnel.....................................................................28
3.7 Comparison Result between Wind Tunnel and Fluid Mapping Table....................................28
3.8 Inappropriate Interior Arrangement...............................................................29
3.9 Interior Wind Simulation....................................................................30
3.10 A. Snow Drop Pattern..........................................................................31
3.10 B. Amelioration of Snow Drop Pattern..........................................................31
3.11 A. Surrounding Effect: Fence..................................................................31
3.11 B. Surrounding Effect: Wall...................................................................31
3.12 Ventilation Amelioration of Site Planning...................................................32
3.13 Wind Simulation of Alternative Design.......................................................33
3.14 Wind Simulation of Typical Building Shape...................................................33
3.15 Summary of Wind Simulation in Building Floor Plan Arrangement...............................34
Thermal comfort 1
Ventilation and Thermal Loads 4
Structural Cooling S
Wind Pressure 8
Stack Pressure 12
Flow Caused by Wind 12
Flow Caused by Thermal Loads 13
Natural Ventilation Due to Both Effects 14
Effect of Height on Wind Speed 14
Natural ventilation is the process that exchanges indoor air for outdoor air without mechanical
power ( Melarago, 1982 ); it is also the un powered airflow through open windows, doors and
other intentional openings in the building envelope.
The circulation of air into the buildings can be divided into two categories :
mechanically-driven circulation and natural circulation. This natural circulation, or the air exchange
between indoor and out door can also be subdivided into: natural ventilation and infiltration
Generally, natural ventilation is induced through buildings by two effects:
1. Wind effect.
2. Temperature effect (or what is called stack effect).
The magnitude of these airflow rates should be known at average conditions to estimate average or
seasonal energy consumption. To began designing with wind for protecting the building or to
maximize the beneficial effects of it, the designer must study the yearly, seasonal, and daily wind
pattern in the area required including the range of wind velocities.
Thermal comfort and healthy environment are the basic requirements as to why air is introduced
Natural ventilation can play a significant role in creating a better situation by modifying thermal
conditions, a bioclimatic analysis for the region can evaluate wind movement by dividing the year
into overheated and under heated periods and define the comfort needs.
By using a bioclimatic design chart, the situations where natural ventilation is effective is shown in
figure 1.1. This shows the bioclimatic chart that Olgay developed in 1963. On the other hand,
using the bioclimatic chart makes it possible to show how comfort limits shift to higher temperature
degree when air velocity increases taking into consideration that increasing the air velocity
enhances the evaporation of perspiration so, the human body will feel thermally
At very low and high levels of humidity the air velocity has a small effect on evaporation since
evaporation readily takes place in the first case and the inability of air to absorb more moisture in
the second case. Therefore, any increase in the air velocity where the relative humidity is between
( 20-80% ) and the temperature above the comfort zone will effect both the convective heat transfer
and the evaporation process.
DRYBULB TEMPERATURE F
GRAINS OF MOISTURE/POUND OF AIR
10 20 30 40 50 60 70 80 90 100
RELATIVE HUMIDrTY %
Figure 1.1 Schematic Diagram of the Bioclimatic Chart (Olgyay, 1963)
When the air temperature is higher than the body temperature both convective heat transfer and
evaporative process act opposite to each other. This leads to the phenomena where below an
optimal air velocity range evaporative cooling is limited and above which convective heat gain is
more effective than evaporative cooling. Figure 1.2 shows the relation between wind speed and
air temperature within the thermal comfort zone for both shade and sunshine.
Figure 1.2 Relationship Between Wind Speed, Air Temperature and Comfort When Strolling,
Calculated for Four Clothing Conditions in Both Sun and Shade.
This Figure shows that the effect of wind speed below 5 mps is very drastic and pronounced.
As mentioned above one of the basic reasons why ventilation is necessary is to control pollutants
inside buildings in order to maintain a healthy indoor environment. It is worth mentioning that
this need does not play a major role in designing buildings as much as the thermal needs,
pollutants have three major sources which must be controlled by ventilation :
1. Pollutants released from building materials and furniture.
2. Pollutants produced within the building:
These pollutants generated by human activities will generate high levels of humidity which will
lead to structural damage. Combustion devices such as stoves or fireplaces have potential to
produce air pollution inside buildings-especially residential buildings. Moreover, back drafting
problems of combustion by products ( Carbon Monoxide Nitrogen, Carbon dioxide ) from
fumeses and water heaters can be threatening health hazards.
3.Pollutants enter the home from the ground below which includes moisture and Radon gas which
is an invisible, carcinogenic gas produced by the decay of uranium in rock and soil. This gas can
be released not only from the cracks between the ground floor and soil but it can be released from
the bricks, concrete or mortar made with sand with uranium content. This Radon gas in high
concentrations increase the risk of developing lung cancer ( Environmental Protection Agency).
Ventilation is quite preferable to unreliable and uncontrollable infiltration. It is also worth
mentioning that in order to get complete ventilation the building must be as tight as possible.
Without a tight building complete ventilation wont be possible and therefore pollutants may
become a problem in certain parts of the building.
VENTILATION AND THERMAL LOADS:
Air exchange typically represents ( 20-40% ) of the buildings thermal load and introduced to the
building constitutes part of space conditioning load, which is a reason to keep the air-exchange
limits to the minimum .
Air exchange increases buildings thermal load in three ways:
1. The air coming from outside to inside must be heated or cooled from the outside to the inside air
The rate of energy is given by :
q=sensible heat load, Btu/h
Q=airflow rate cfm
G=air density Ibm/f ( about 0.075 )
Cp=specific heat of air, Btu/lbf ( about 0.24 ).
2. Air exchange increase the moisture content in buildings, the energy rate consumption associated
with these loads is given by:
q 1 =60Qhfg(wi-wo)
ql=latent heat load, Btu/h
hfg=latent heat of vapor at appropriate air temperature Btu/Ibm
3. Air exchange can increase the thermal loads by decreasing the efficiency of the envelop
insulation system. Airflow around the insulation can increase the heat transfer above the design
rates, and airflow within the insulation system can produce moisture which will decrease the
When the ambient temperature and wind is not preferable and when only the night time
temperatures fall into the comfort zone, natural ventilation is also used to cool the structure in order
to make the temperature fall into the comfort zone during day time. Careful design criteria for
ventilation and mass are used to accomplish this.
To find the approximate cooling performance for a building the flowing steps must be considered:
Find the expected minimum mass temperature by subtracting the maximum temperature of the place
in which the building placed from the mean daily range and adding the amount of temperature that
the internal mass gets, which is a ratio of the mean daily range.
After that one can find the estimated heat gain from the tables shown in table (1).
Using simple charts, design guide lines for cooling the building has been developed by estimating
the inlet/outlet area required to remove the heat gain and cool the building.
Chart no. ( a,b ) shows the approximate heat store of the internal mass during day time for average
mass structure by assuming that the outside temperature should be at least (3 degrees F) above the
inside temperature in the day time. This mass equal to the total of the floor area multiplied by
4 inches of ordinary-density concrete slab. These charts helps to chose the appropriate mass that
will capture the heat gain through the building.
Mean daily range
(22.2) (19.4) (16.7) (13.9) (11.1) (C)
Mean daily range
Chart no. ( c ) is used to estimate the maximum hourly cooling rates percent of the storage capacity
which can be removed from the structure at night.
(22.2) (19.4) (16.7) (13.9) (11.1) (C)
Mean daily range
The below two charts used to find the inlet outlet area required to remove the heat from the
building within 10% of accuracy and how much heat can be removed per unit floor area for both
cross ventilation and stack ventilation respectively, also, it shows the relationship of area inlet
opening and wind speed by taking into consideration that the internal temperature is (3F) above the
exterior temperature, the graph indicate the required inlet area for the cooling load that has been
estimated from chart no. (c)
Cross ventilation capacity
Btu/h ft2 (W/m2)
Stack ventilation capacity
When the temperature difference is not 3F chart no. (d) is used to estimate the temperature
difference for using it in the factor ( 3F/Ti-To) to calculate the inlet area by multiplying this
number with the percentage estimated from the above charts.
Maximum hourly AT
Mean daily range
These charts are simple to use for estimating the area of ventilation by wind inducing or by stack
effect or even by forced ventilation as a rule of thumb.
Figure 1.3 shows heating and cooling strategies for various types of climate, including the zone in
which we can use natural ventilation and mass as integrated parts for cooling the structure.
80 60 40
50 70 80 90 (F)
10 21 26 32 (C)
Figure 1.3 Design strategies based on climatic conditions by Givoni (Stein, 1986)
When airflow occurs around a building it creates positive pressure on the windward side and
negative pressure in the leeward side.
The greatest wind pressure will be when it is 90 degrees to the surface of the building. At 45
degrees, the pressure is reduced about 50%. High surface to volume ratio, with maximum
exposures to the wind, can maximize pressure for natural ventilation. Building shape and height
affects the wind pressure.
The wind pressure is given by Bemoulles equation:
Pv=C 1 CpGsq.V/2
Pv=surface pressure relative to the static pressure in the undisturbed flow, in. of water
Cl = unit conversion factor
Cp=surface pressure coefficient
G=air density, Ibm/cub.ft (about 0.075 )
V=wind speed, mph
The density indicated in this equation depends on the speed of the wind, the height of the location
and the temperature. On an air temperature change from (20-70F), the air density will drop about
20%. Also, the wind speed in the buildings is lower than the average meteorological wind speed
for a region.
Wind Coefficient (C):
The value of the wind coefficient (C) depends on building shape, wind direction and the
surrounding influences. Determining (C) can obtained only from wind tunnel scaled models for a
specific site. For simple rectangular shapes existing wind tunnel data can be used to determine
ventilation rate calculations. Figure 1.4 shows wall pressure coefficients on walls for low rise
buildings where H
wind, the pressure coefficients are positive and increases at the edges and wind velocity increases.
Also, the increase of the coefficients as height increases indicate that the increase of velocity
As the wind angle increases the maximum wind pressure occurs at the top edge of the windward
side, and maximum suction pressure occurs near the up wind edge at 90 degree. In figure 1. 5 the
surface pressure coefficient over a complete wall is illustrated (Swami and Chandra, 1987).
Figure 1.6 shows typical pressure distribution for a wind direction normal to windward side of the
building which indicate that pressure on the roof depends strongly on roof slope.
As the degree angle of the slope increases, the pressure began to change. For a low slope up to 15
degree the pressure is negative over the whole roof surface and is maximum near the edge of the
windward side within the separated flow zone. With steeper angles the pressure over the
windward slope becoming positive and negative over the leeward side.
Figure 1.7 shows the relation between angle and dimension of the building and the roof pressure
coefficient over a roof.
Internal Heat SourcesPeople and Equipment
Area per Person Sensible Heat Gain (Btu/h ff of Floor Area)
Function (ff) Peoplea Equipment0 Total
Office 100 2.5 3.4 5.9
School: elementary 100 2.5 3.4 5.9
School: secondary, college 150 1.7 3.4 5.1
Hospital 100 2.5 Varies 2.5 plus
Clinic 50 5.0 Varies 5.0 plus
Assembly: theater0 15 15.3 15.3
Assembly: arena0 15 16.7 16.7
Restaurant 25 11.0 Varies 11.0 plus
Mercantile 50 5.0 Varies 5.0 plus
Warehouse 1000 0.4 0.4
Hotels, nursing homes 300 0.8 3.4 4.2
Apartments0 300 0.8 (see note d) (see note d)
Part B. Internal Heat SourcesLighting, Daylight and Electric
Sensible Heat Gain (Btu/h ff of Floor Area)*
Function DF < 1 1 < DF <4 DF > 4
Office 5.1 2.0 0.5
School: elementary 6.3-6.8 2.5-2.7 0.6-0.7
School: secondary, college 6.3-6.8 2.5-2.7 0.6-0.7
Hospital 6.8 2.7 0.7
Clinic 6.8 2.7 0.7
Assembly: theater0 3.8 1.5 0.4
Assembly: arena0 3.8 1.5 0.4
Restaurant 6.3 2.5 0.6
Mercantile GO CD I in 2.0-2.7 0.5-0.7
Warehouse 2.4 1.0 0.2
Hotels, nursing homes 6.8 2.7 0.7
Apartments0 Up to 6.8 Up to 2.7 Up to 0.7
Part C. Heat Gains through Envelopef (Btu/h ft2 of Floor Area)
90 F 100 F
Gains through externally shaded windows:
. total window area
total floor area
Gains through opaque walls:
. total opaque wall area ... ,
Find ----. ,,---------- X (tVwan))
total floor area
Gains through roofs:
total opaque roof area ,,, v
f,M total floor area *
then multiply by 16
then multiply by 15
then multiply by 35
Table 1.1 Approximate Heat Gains( Mechanical and Electrical Equipment for Buildings(7th
ed., pp. 189)
t 1 0.8
1 t / 1
106 / 06 o o /
/ / / / ^ /0.1
r t t
Figure 1.4 Mean Pressure Coefficients on the Walls of a Low-Rise Building (Holmes 1986).
Figure 1.5 Variation of Wall Averaged Pressure Coefficients for a Low-Rise Building (Swami
and Chandra 1987)
Figure 1.6 Pressure Coefficients on the Roof of a Low-Rise Building (Holmes 1986).
Figure 1.7 Average Roof Pressure Coefficients .
Temperature differences between inside and outside caused density differences which will cause
pressure difference and therefore infiltration.
In the heating season the warm air will rise and be replaced by the cold air which enters the
building near its base. During the cooling season the flow is reversed and is lower due to the fact
that the temperature difference is smaller. Qualitatively, the pressure performance will be as
indicated in figure 1.8 .
The point at which the interior and exterior pressures are equal is called the neutral pressure level
(N.P.L). Above this point the interior pressure is greater than the exterior pressure during the
Figure 1.8 Pressure Differences Caused by Stack Effect for a Typical Structure ( Heating ).
Arrows indicate magnitude and direction of pressure difference.
FLOW CAUSED BY WIND:
To remove a certain amount of heat from a building using ventilation, airflow can be calculated
Q=airflow required to remove heat, cfm.
H=heat to be removed, Btu/min.
C=specific heat of air, Btu/Ibm (about 0.24).
G=air density Ibm/cub.ft
When wind blows around a building pressure difference occurs between the leeward and wind
ward sides. If an opening exist in both sides, airflow will occur from the positive to the negative
side of the opening. This flow will be affected by wind speed, prevailing direction, and local
abstraction near the building. Several methods have been used to calculate the flow induced by
wind; each of them has its advantages and disadvantages. These models are:
1. ASHRAE MODEL.
2. DISCHARGE MODEL.
3. IHVE MODEL.
4. COMBINED MODEL.
5. VICKEUY MODEL.
The ASHRE model is chosen to be discussed here because of its simplicity. It requires wind
velocity and the area of inlet and outlet which, however, will affect the accuracy of prediction.
The equation of this model is in the form of:
C=effectiveness of openings (C is assumed to be 0.5 to 0.6 for perpendicular winds and
0.25 to 0.35 for diagonal winds)
A=free area of inlet opening
Inlets should be directed to the prevailing wind. A correction chart related to this model is available
in Building Climate and Energy (Markus 1980).
The selection of an appropriate model depends on the building simplicity and the resources exist.
FLOW CAUSED BY THERMAL FORCES:
When the temperature of the bottom air increase a convective process occurs because of the
deference in density between the bottom and the top part, this causes hot air to rise and replaced by
cold air, this called chimney effect.
The major factors affects this phenomena is the difference in height between the inlet-outlet and
temperature difference which increase when increase one of these components .
When there is small internal resistance, the flow caused by the stack effect can be calculated by:
K=discharge coefficient for opening (9.4-7.2)
hnpl=height from lower opening to npl, ft
C=unit conversion factor (60) (ASHRE, 1989)
This equation applies when (ti) is greater than (to), if not, (ti) must be replaced by (to) and (ti-to)
by (to-ti). Inlets and outlets are considered to be equal, where opening are not equal, the smaller
area must be used in the equation and add the increase as indicated in figure 1.9.
RATIO OF OUTLET TO INLET OR VICE-VERSA
Figure 1.9 Increase in Flow Caused by Excess of One Opening Over Another.
Stack pressure is extremely minimal compared with wind pressure except for high rise buildings
where the wind pressure increases with the square of wind velocity while stack pressure increases
linearly with the height and temperature differences.
In hot climates, using stack effect for ventilation as a major part is not recommended when
compared to the cold regions, where the temperature difference between the outside and the inside
is 80-90 respectively, unless certain technique like the solar chimneys and shafts are used. On the
other hand, controlling and predicting the direction of the flow is usually very small because of the
low velocity that can be achieved using this method.
NATURAL VENTILATION DUE TO BOTH EFFECTS:
The combine effect is the algebraic sum of both effects, although the two effects may or may not
act in the same direction. This depends on the wind direction and the difference in temperature
between inside and outside.
EFFECT OF HEIGHT ON WIND SPEED:
As the distance from the ground increases the velocity of the wind increases due to the retarding
and friction effects of the earth.
Wind speed is zero at the ground and increases with the height up to altitude of about 2000 ft above
ground level. Meteorological measurements are usually taken at height of 33ft. Above 200 f.p.m
air becomes a source of draft and noise in enclosed places. Above 850 fpm there will be no
comfort benefit to increased air speed.
Velocity profiles depend on the terrain type. Figure 1.10 shows the mean velocity profile for open
country, suburban and city centers which was reported by Aynsley (1974).
2000 FEET Z
Z0 =12 in.
A0 = 0.60
a = 0.28
Z0 =120 in
Aq = 0.35
a = 0.40
Z0 = 1.2 in.
A0 = 1.0
a = 0.15
Figure 1.10 Typical Wind Speed Profiles Over Different Terrain Roughness.
Types of wind tunnels 16
Basic Requirements for the Simulation 20
No satisfactory theory can describe or predict all the possible variations in airflow. When the wind
became a vital issue in the design, the wind tunnel was used to test the patterns and pressure of the
wind. With the wind tunnel, problems may be analyzed and by redesigning certain parts of the
building and testing it again, time and money can be saved. Strong winds can cause the tall towers
of some buildings to sway so that the exterior walls creak and the elevators will not operate. Rapid
changes in air pressure will cause windows to break and disturb heating and ventilation systems.
These conditions appears generally in buildings that are at least five times as tall as they are wide.
The purpose of wind tunnels in environmental research is to physically simulate the wind with an
appropriate scale in order to facilitate observing and measuring natural winds effect on buildings(Al-
Since 1759 when a scientist named Smeaton examined wind forces on objects, efforts have been
made in two ways:
1.) by building large wind tunnels where models can be tested; and 2.) by improving advanced
techniques to establish similarities between modeled and natural flows.
TYPES OF WIND TUNNELS:
Winds are so complicated that the only possible way to predict their precise effects on a building is
through measurements in a scale model. To model strictly by computer is a long way off, if
Researchers construct a scaled model of the proposed structure and its environment, place it in the
test section of the wind tunnel and start the fan. The model can have as many as 400 pressure sensing
points -tape holes- all of which are connected by plastic tubing to ultrasensitive stain gauges and the
gauges start to measure the fluctuations that are analyzed by computer. A visual record of the wind is
made by photographing a chemical smoke. Researchers study the results looking for an abnormally
high or low pressures that could cause problems.
Cermak (1971) mentioned three basic types of wind tunnels:
1. Meteorological Wind Tunnel (M.W.T.)
This close circuit wind tunnel fulfills the basic research on flow characteristics of the atmospheric
boundary layer (ABL) like pollutants wind pressure of buildings, also for generation of thermally
stratified flows,most frequently used to study individual buildings. Strong wind simulation on
structures are possible by this wind tunnel.
Wind tunnels used in testing aircrafts are designed with short test sections, the goal is to produce
uniform wind speed and temperature through out the tunnel, but to simulate meteorology of an area a
wind tunnel of a test section 15times as long as its height to produce proper temperature distribution
for both air and land for the test section floor as will as the air interning the wind tunnel must be
controlled which means that a closed recirculating system is a must.
This kind of wind tunnel can vary wind speed pressure humidity and air temperature at various
heights and is available only at Colorado State University, figure 2.1.
Figure 2.1 Meteorological Wind Tunnel, Fluid Dynamic and Diffusion Laboratory, Colorado
Figure 2.2 Industrial Aerodynamics Wind Tunnel, Fluid Dynamic and Diffusion Laboratory,
Colorado State University.
Figure 2.3 Environmental Wind Tunnel, Fluid Dynamic and Diffusion Laboratory, Colorado
2. The Industrial Aerodynamics Wind Tunnel:
This is a closed circuit wind tunnel designed by Cermak. This wind tunnel is used for strong wind
simulation. The primary use of this wind tunnel is for aeronautical research, figure 2.2 .
3. The Environmental Wind Tunnel:
This is an open circuit wind tunnel which used for model studies of flow over cities, tall structures
and topographic features. With strong winds, turbulence occurs and produces a destruction of the
temperature layers in the atmosphere. The prime requirement for the environmental wind tunnel is
that the length of the test section be at least 10 times its height. Most of the existing small wind
tunnels are of this type. It is worth mentioning that a close circuit system provide better control than
an-open circuit, figure 2.3 .
BASIC REQUIREMENTS FOR SIMULATION IN WIND TUNNELS:
Because of the extreme complicity that affects winds at the atmosphere boundary layer -the lower 100
to 2000 feet of atmosphere affected by the earth surface friction as it moves over cities forests,
lakes, etc., special wind tunnels has been developed by providing a flow field of varied mean
velocity and temperature to simulate the wide range of flow structures that occurs in the atmospheric
boundary layer. While wind tunnels that provides a test section flow field of uniformly mean
velocity and temperature and a low level of turbulence are used for aeronautical.
The basic requirements for simulation of atmospheric boundary layer and strong wind of buildings
1. Understanding the scaling of boundary geometry, (Geometric similarity).
2. Dynamic similarity Reynolds member equality
3. Thermal similarity, Rossby number equality
4. Kinematic similarity of approach flow
1. Geometric Similarity:
The geometric scale of the model is influenced by two parameters:
a) The allowable of blockage area:
The velocity and cross section of the wind tunnel are functions of the blockage ratio. Generally
blockage ratio is 2.5-10% of the tunnel cross section area .(Aynsley,1974; ASHRA 1981)
b) The maximum attainable boundary thickness within the tunnel test section:
The wind tunnel must be capable of developing a turbulent boundary layer thickness from 1-2 times
as great as the height of the modeled structure ( Cermak, 1979). By knowing the height of the model
the upper limit of the scale ratio am be determined. By checking the models cross sectional area the
blockage ratio can be verified and if not adequate the scaling process can be repeated.
2. Dynamic Similarity:
The equality of the appropriate dimensionless numbers in both model and prototype would lead to
similarity between the model and prototype.
In order to achieve similarity of effects between model and prototype flows, the equality of Reynolds
and Rossby numbers in both flows should be maintained(Cermak, 1971)
Reynolds and Rossby numbers:
Physical and geometrical quantities that affects wind force can be analyzed using pie- theorem (Arpaci
n=earths circular frequency
this can be arranged to be written as :
m/gDV is the Renynolds number
Dn/V is Rossby number
Because large wind tunnels cannot be rotated easily the requirement of equal Rossby number must be
relaxed due to the fact that the rotation of earth causes the mean wind to change direction by about 5
degree over a height of 200 m. This relaxation of the equality of this number fortunately will not
affect the simulation of the flow. When the atmospheric Rossby number is greater than ten, the
inequality in this number between the model and the prototype will not affect the accuracy of the
simulation (Cermak, 1975).
On the other hand, the equality of the Reynolds number indicates that the turbulence of both flows are
quite similar. In order to achieve the equality, an increase in the velocity or a decrease of the
viscosity of the model flow must be considered.
In studies where thermal effect is to be accounted, three additional dimensionless numbers have to be
1. the Prandel number mC/K
2. the Richardson number (Ql-Q2/Ql)(gl-g2/sq.V)
3. the Eckert number sqV/CQ
The only wind tunnel equipped with heating and cooling facilities that enables simulating temperature
stratification is the meteorological wind tunnel which can be found at Colorado State University in Ft.
4. Kinematic Similarity:
The major factors for this type are shapes and distribution of mean velocity and turbulence
In order to achieve these similarities, basic similarities must occur:
1. Aerodynamic effects of the surface roughness.
2. The wind tunnel must be capable of developing a turbulent boundary thickness from 1 to 2 times as
high as the height of the modeled structure.
3. The vertical mean wind distribution velocity and the longitudinal turbulence intensity of the wind
tunnel have to be similar to the prototype flow.
4. The blockage area should not be more than 10% of the total cross sectional area in order to keep
the longitudinal pressure gradient equal to zero.
Wind and air quality conditions vary enormously from one building site to another. Wind tunnels
became a vital issue in the study of wind effect in high rise structures because of the complexity of
the boundary conditions where wind cannot be described by numerical or analytical methods. With
the use of wind tunnels our inability to describe wind flows interacts with people, buildings,
vegetation and topographic features can be dissappear and by using this knowledge the damage
caused by the strong wind can be eliminated or cut.
On the other hand, wind effect data can be measured in wind tunnels to establish a set of magnitudes
for a simple reference in order to be used as design criteria that would help to feed the computers for
determining wind forces, moments and peak pressures.
FLUID MAPPING TABLE
Physical Configuration of a Fluid
Mapping Table 25
A comparison Between Fluid
Mapping Table and The Wind
Design Application 29
FLUID MAPPING TECHNIQUE:
This section investigates the airflow around and through an object by utilizing water as a means to
simulate the patterns of the wind (Fluid Mapping Technique).
To verify reliable results, a wind tunnel was built for calibration purposes. Visual analysis of the
flow pattern from the fluid mapping table and the smoke from the wind tunnel were studied using a
frame by frame analysis of recorded video images The speed of the water and the scale of the object
were also investigated and compared with the results from the wind tunnel.
For a general design application of an airflow with reasonable accuracy Fluid Mapping Technique
offers a good alternative approach at a very low cost. It is also easy to operate and less time
consuming. With some experience and careful investigation, this technique proves to be a very
powerful design tool with a wide range of applications, whether to enhance design performance or to
investigate a design alternative.
This study will utilize the advantages of the Fluid Mapping Technique to explore a variety of
building shapes, including the interior and exterior, commonly designed today. This study tries to
emphasize the use of a natural ventilation potential for design application.
An ability to predict airflow patterns is very useful for any designer. For an architectural design
application, air movement across the living space will provide natural ventilation, remove heat and
cause a cooling effect when the air flows across the skin. In landscape and site planning, the
knowledge of airflow patterns will aid the designer in assuring a potential for natural ventilation and
allowing examination of snow drop patterns and contaminant zones for the site.
Today, wind tunnels are widely used to accurately predict airflow patterns. This technique,
however, can be very expensive, time consuming and may not be appropriate for general design
The "Fluid Mapping Table" technique offers a good alternative approach for general design
application at a very low cost and is less time consuming. The inaccuracies of this technique,
however, can lead to unreliable results unless careful analysis and interpretation is performed. With
some experience and careful investigation, this technique can be a very powerful design tool with a
wide range of applications. The dynamic pattern of airflow, whether with steady wind speed or
unsteady wind speed, can also be simulated successfully, with much less difficulty, using this
PHYSICAL CONFIGURATION OF A
FLUID MAPPING TABLE:
The "Fluid Mapping Table" used in this study consists of a smooth simulation plane of a translucent
plastic material illuminated from underneath as shown in Figure 3.1. It is important that the table be
perfectly level to assure the same speed throughout the cross section of the table.
The depth of the water on the simulation surface should be maintained at a very thin layer to minimize
double flow action at the top and bottom layers. The dye inducer is used to control a smooth parallel
flow line during simulation. The dye or the ink used for the simulation should be reasonably
controlled and dissolve very slowly in the water in order to see a clear flow pattern. In this study
potassium permanganate dissolved in the water is used. This chemical produces a clean pattern, is
less costly than ink and quite safe to use for this purpose. It will however, stain most materials and
human skin with prolonged contact.
DYE INDUCBR [~WAT8R PLOW
Figure 3.1 Configuration of fluid mapping table
The use of the "Fluid Mapping Technique" can only provide two dimensional flow patterns with the
assumption that the cross section of the object used has an infinite length. The three dimensional
aspect of the flow pattern, however, may be visualized by studying the flow pattern from both the
section and the plan of the object.
SCALING AND VELOCITY EFFECT:
It must be recognized that the viscosity of water and air are not the same. Air has much less viscosity
than water. This suggests that air has a better capability to fill up the opening gap than the water.
Therefore the use of water to simulate airflow patterns of an object would be less sensitive.
The scale of the model used may produce a similar error; a model with a very small scale would
provide less sensitivity to flow action, and a very large scale would result in insufficient or uneven
flow in some parts of the simulated object.
This study attempts to duplicate the wind flow patterns found in Design With Climate ". A scale of
1 inch = 1 foot was used with a water flow rate of 3 inches per second. This is equivalent to 2.04
miles per hour in the actual environment. This setting seems to generate the best result with respect to
the above objective.
LONG SHADOW EFFECT:
The long shadow effect is the result from the water flow is two slow. Reasonable water speed must
be investigated to prevent this phenomenon.
Figure 3.2 Long shadow effect
DELAY ACTION OF THE FLOW LINE:
The effect is the result of the bounding action of the water in the lower layer near the surface of the
simulation table. To assure an accurate interpretation of the result, observation must be made at the
early stage when the flow action of the top layer of the flow is in effect.
This distance is delay action created by the reflection of water in the lower layer.
Figure 3.3 Delay action of the flow line.
IDENTIFY THE WIND SHADOW ZONE:
The boundary of shadow zone, contaminated zone or Eddy effect is very difficult to identify. A
simple approach may be achieved by injecting the large quantity of dye on to the interested zone, the
dye outside the shadow zone will be carried away by the active flow of water, the remaining dye
pattern will signify the boundary of shadow zone.
D:Dislance of wind shadow
Figure 3.4 Identify the wind shadow zone.
AN INTERPOLATION OF A RESULT
HIGH AND LOW PRESSURE ZONE:
A high pressure zone may be observed by the action of the flow line and the flow of the water. The
more perpendicular the flow line is to an object's windward side the higher the static pressure
created. A parallel between the flow line pattern and the surface of the object would suggest a neutral
pressure zone, the less disturbed area on the leeward side of an object would suggest a low pressure
zone. In general, if there are openings, the wind will flow from a higher pressure zone to a lower
one. Figure 3.5 illustrates that different pressure zones occur around an object. The width of the
flow line also indicates the speed of the wind around the object. The closer together the flow lines,
the higher the wind speed.
NEUTRAL/ LOW HISSURS ZONE
LOW PRBUURB ZONH
HIGH PRESS RE
Figure 3.5 Different pressure zones around building.
A COMPARISON BETWEEN THE FLUID
MAPPING TABLE AND THE WIND TUNNEL:
There will be no attempt here to compare the results of the wind tunnel and the "Fluid Mapping
Table" using a scientific approach. The comparison discussed here will be based on a visual
observation of a recorded image from a video camera.
For the purpose of studying, a wind tunnel was built with the intention to compare a smoke pattern
generated by a three-dimensional model from the wind tunnel and a two-dimensional flow pattern
from the Fluid Mapping Table Figure 3.6 shows the configuration of the wind tunnel at the
University of Colorado at Denver. It is capable of generating a wind speed of up to 600 F.P.M. Even
though this wind tunnel was not equipped with the ability to adjust for complexities of boundary
conditions and thermally related issues, it has, however, been modify to a certain degree to facilitate
The results shown in Figure 3.7 are the results of a frame by frame analysis of selected dimensions
and patterns. In the case of the wind tunnel the pattern plan was obtained from the top view of
objects in the simulation chamber and the pattern section was an image of the side elevation. The flow
pattern in the "Fluid Mapping Table" came from two separate experiments, the floor plan and section
Figure 3.6 Configuration of wind tunnel:
As might be expected these dimensions and shapes of the patterns shown are average results with a
relatively large degree of variations in all cases. They are not very easy to obtain without the
recorded image of the video camera.
SECTION SIMULATION WINO TUNNCl FlUIOMAPP.
1 a 1
Figure 3.7 Comparison result between wind tunnel and fluid mapping table.
The actual airflow pattern around a building and within an interior space, especially for a complex
shape and unusual arrangement, is very difficult to predict. This is due to the fact that the wind
velocity and wind direction is constantly changing. The change in both the wind speed and direction
would constantly create pressure differences between the windward and leeward side of the building.
This change will result in a dynamic change of flow pattern which in many cases cannot be easily
predicted by any simple approach. To fmd the overall performance of a building at all times, a
simulation approach is necessary. The following are some selected case studies utilizing the "Fluid
Mapping Table" as a design tool.
VENTILATION FOR AN INTERIOR SPACE
The interior arrangement of spaces, partitions, furniture, equipment, etc. may have a major effect on
air circulation. For buildings which rely on mechanical system ventilation, the supply and return air
pattern must recognize the arrangement of the interior partition as well. Figure 3.8 shows the
inappropriate arrangement of such a pattern. The use of a simulation technique would help in
eliminating such problems.
RETURN AIR SUPPLY AIR
INSUFFICIENCY OF VENTILATION GOOD VENTILATION
Figure 3.8 Inappropriate interior arrangement.
For buildings which rely on natural ventilation, the shape, form and opening of a building are also
important. Figure 3.9 below illustrates some conditions that may be difficult to predict without a
The wind pattern is controlled by the partitions and louvers which, in the case of Figure A, redirect
the airflow downward toward the living area and upwards in the case of Figure B. In both cases
there is no wind entering from the roof opening on the windward side of the room.
Figures C and D show the wind entering the roof opening on the windward side. This is caused by
the modification of other openings to create a greater pressure difference between the inlet and the
outlet of the roof opening.
Figures E and F show that changing the structure of the wind catcher results in modifying the
velocity of the wind in the wind catcher and this leads to a change in the direction and velocity of the
INTERIOR WIND SIMULATION
OPENING POSITION AND SIZE
wind direction ROOf Enclenation ^ 45 | 1 | One unit | 2 I Two Units
Figure 3.9 Interior wind simulation.
The site analysis may include the potential for natural ventilation, winter wind protection, snow drop
area, contaminated zone, etc.
Figure 3.10.A shows a problem area as a result of snow deposits below the two groups of
buildings. In this case, with a large object such as a round building or a dense group of evergreen
trees in the middle, a major part of the problem may be eliminated as shown in Figure 10.B.
Figure 3.10 A. Snow drop pattern.
B. Amelioration of snow drop pattern.
Figures 1 l.A and 1 l.B show a comparison of airflow through the building. An open fence as shown
in Figure 12.A would allow less airflow through a building than the solid fence in Figure 1 l.B.
Figure 3.11 A. Surrounding effect : Fence
B. Surrounding effect: Wall
Figure 3.12 illustrates the change in airflow pattern through a building complex. Figure 3.12.A
shows no air circulating through the building when the site is modified with a large tree as shown in
Figure 3.12.B or a wall in Figure 3.12.C. The wind was redirected into the building as a result of
surrounding elements. In the case of Figures 3.12.B and 3.12.C the surrounding site element
created some pressure differences between the two sides of the building forcing the wind to flow
through the open window.
Figure 3.12 A-C. Ventilation amelioration of site planning.
The arrangement of Figure 3.13 shows the comparison of different masses. Figures 3.13 A through
3.13 C show the arrangement of the circular complex which experiences large variations in natural
ventilation potential. In Figure 3.13 A a major part of the complex did not receive sufficient
ventilation. The modification as shown in Figure 3.13 B significantly improved the ventilation
potential of the complex. With a slight adjustment in Figure 3.13 C of the center mass all
components of the complex received sufficient ventilation.
Figure 3.13 A-C. Wind simulation of alternative design.
Figure 3.14 shows some typical arrangements of the building floor plans. It can be seen very clearly
that part of these buildings did not receive proper ventilation when the wind comes from certain
Figure 3.14 A-D. Wind simulation of typical building shape.
Figure 3.15 is an overall summary of a building floor plan arrangement which could be used as a
guideline for planning.
WIND SIMULATION OF BUILDING MASS
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Figure 3.15 Summary of wind simulation in building floor plan arrangement.
Within a micro-climate in a natural environment setting, the force that causes air movement through
and around buildings is primarily the result of the difference in wind speed, its direction and the stack
effect created by the warm air rising. These forces, in conjunction with the difference in the design
elements of landscape fixtures, building form orientations, openings, building components and
interior configurations, make it very difficult to accurately predict the wind flow patterns which occur
within and outside the building.
The use of the Fluid Mapping Technique eliminates most of the guess work error in the prediction.
It is also possible to investigate many design alternatives at a very low cost in a short period of time.
It also allows for better design integration between site planning, building design and interior
arrangement of spaces, some of which have been demonstrated in this paper. This technique is not a
perfect representation of the actual wind flow or a substitute for an investigation using a wind tunnel.
However, it has been used as part of the design process in many successful projects.
Airflow movement should be considered as important as other aspects at the primary design stages
knowing a knowledge in using wind flow and practicing it reduces the energy consumption .human
comfort as will as eliminating the damage caused by strong winds.
Desirable air movement could be utilized for cooling buildings in hot seasons as will as air
movement should be blocked during cold periods.
Wind knowledge nowadays considered to be an important requirement for designing building and
structures. The importance of having a knowledge about wind takes place in two ways :
1. Knowing the specific characteristics of wind flow around the object (wind engineers):
a) Designing for tall buildings ( high rise buildings ):
In this case general or specific codes cannot take control and basic knowledge in wind characteristics
and calculations cannot be useful. A specific knowledge with accurate information for designing
those kind of structures can be done only by simulating the cases individually for the wind patterns,
pressure, moments and loads in a scaled model with a similar boundary conditions as the prototype
by using wind tunnels.
b) Solving an existing and not predictable problems.
2. Estimate a knowledge for wind flow direction and capability:
This knowledge can be used for low rise buildings and basic research studies using wind as a tool for
energy consumption by (getting red of the generated heat) or cooling the structure. Calculations and
building codes can be used efficiently which can be strengthen by simulating wind flow patterns
when there is a difficulty to accurately describe wind flow patterns. At this case Fluid Mapping Table
which provides better solution for designers than wind tunnels because of the possibility for the
investigation at a very low cost with a short period of time for most design applications can be the
INTERIOR WIND SIMULATION
NTERIOR WIND SIMULATION
Louver Angle Changing In an InciindRoof
OPENING POSITION AND SEE Partition
LEFT SIDE SPEED RIGHT SIDE SPEED ROOF OreNING >
location location LEFT STCED RIGHT SPEED
Size Low Size High 0 O 180
Size Normal Size High 0 o 210
Size High Size High 0 n 240
Size Normal Size High 0 0 30
Size High Size High 0 0 60
1. The major wind
direction is controlled
by the partitions and
louvers wich can be
controled to match
with different type of
2. No wind is entering
from the upper opening
no matter what
direction of the louver.
3. Using this concept
for summer ventilation
is recomended so as to
get rid of the hot air
that will gather in the
upper level and may
circulate to the lower
level and affect the
comfort of the user.
4. To acheive getting
rid of the upper air and
preventing it entering
to the inside of the
space, the relation
betwen the roof-inlet
and the wall-outlet
must be controlled; the
outlet must be smaller
than the inlet.
INTERIOR WIND SIMULATION
Existing Operating el
3 No Operating wind direction
INTERIOR WIND SIMULATION
OPENING POSITION AND SEE
ATTACH DETACH ANGLE
Existing Openning *J
> No Openning =? wind direction
The overhang collects air streams and enhances incoming flow
Air flow patterns is greatly affected by the louver direction.
Depending upon the funcuon, the louver or the overhang unit
iition can be selected to match with this function.
fERIOR WIND SIMULATION
Implementation Of Diffrent opening Size And Location In Inclind Roof
OPENING POSITION AND SIZE
LEFT 5FEBD RIGHT
1. Having two openings
in the roof allow the
wind to penetrate
through them taking the
hot air outside, but some
of it circulate to the
2. Changing the size of
the opening while
having the same location
leads to chang not only
velocity but also the air
with the structure.
3. Having the same
outlet wall and inlet roof
opening size creates air
movement from the roof
inlet to the wall outlet
while if the outlet is
smaller than the inlet the
air will not move from
the inlet to the outlet
Existing O penning
ion ^ 45
| 1 | One unit
m Two Units
INTERIOR WIND SIMULATION
Roof Shape Openings
OPENING POSITION AND SIZE
LEFT SPEED RE ITT SPEED
1. The two openings in
the roof allow the wind
to blow through them
and get the hot air
outside, but some of it
circulate to the inside.
2. Changing the types of
roof openigs can control
the direction and
velocity of the inside air,
so, one can direct the
wind to the point he
3. This type of
arrangement can be used
for both summer
ventilation and winter
wind protection ; in the
summer the hot air can
be removed from the
upper side when it
reachs certain point and
in the winter the hot air
can be circulated by
closing one of the upper
INTERIOR WIND SIMULATION
Changing The Roof Shape With a Cross Vetilation Opening
OPENING POSITION AND SIZE
LEFT SPEBI RIGHT SPEED
1. Having two opening
in the roof allow the
wind to panatrate throw
them taking the hot air
outside, but some of it
circulate to the inside.
2. Changing the roof
openigs types can
control the inside air
movement, ditection and
velocity, so, with little
effort one can direct the
wind to the point he
needs in accuracy.
3. When having an
opening facing the wind
direction, changing the
roof opening shape will
make the possibility for
4. (45) Degree Angle for
the top roof opening
with the other openings
is not suitable for
5. (135,90) Degree
Angles are suitable for
summer ventilation, also
the other angles can be
used with careful
considerations like the
size and location of the
Existing Openning wid direction ROOf Enclenation ^ 45 | 1 | One unit 12 | Two Units
o No Openning
INTERIOR WIND SIMULATION
Comoplex Cross Section Study
OPENING POSITION AND SIZE
LEFTSIDE SPEED RFGFTTSIDE SPEED
Wind Catcher speed
o No Openning
1. The Fluid Mapping
Table can be used to
2. Any change in the
structure changes air
movement and velocity.
3. Simple design
alternatives with small
changes control air velocity
4. Changing the structure of
the wind catcher results in
changing the velocity in the
wind catcher and this leads
to change in the direction
and the velocity of the air
(changes the indoor air
MASS WIND SIMULATION
1 This section has been done with the help of my colleagues chen Hwai
WIND SIMULATION OF MASS conclusion 1
INSUFFICIENCY OF NATURAL VENTILATION
WIND SIMULATION OF MASS CONCLUSION 2.
BASIC SHAPE WIND DIRECTION
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INSUFFICIENCY OF NATURAL VENTILATION
Al-Megren, Khalid Abdullah. Wind Towers for Passive Ventilation Cooling in Hot-Arid
Regions doctoral dissertation, University Microfilm, 1987.
Carby, L. Low Speed Wind-Tunnel Operation and Maintenance Manual: Manual for
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Cook, N. A Boundary Layer Wind Tunnel for Building Aerodynamics, Vol. I, No. 1,
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