Wind tunnel tests in the field of industrial aerodynamics

Series Hy:

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Hy-1 PROHASKA, C. W. Analysis of Ship Model ExperIments

and Prediction of ShIp Performance 5,00

(Second printing)

Hy-2 PROHASKA. C. W. Trial Trip Analysis for Six Sister Ships 6,00 Hy-3 lLOVl& V. A Five Hole Spherical Pitot Tube for 6.00

Three Dimensional Wake Measurements Hy-4 STRØM-TEJSEN, J. The HyA ALGOL-Programme for Analysis

of Open Water Propeller Test

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:Hy-5 ABKOWITZ. M. A. Lectures on Ship Hydrodynamics - 20.00

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Hy-6 CHISLETT, M. S., and

STR0M-TEJSEN, J.

Planar Motion Mechanism Tests

and Full-Scale Steering and

12,00

Manoeuvring Predictions for a

MARINER Class Vessel

Hy-7 STRØM-TEJSEN, J., and A Model Testing Technique and 12,00

CHISLETT, M. S. Method of Analysis for the Prediction of Steering and Manoeuvring Qualities

of Surface Vessels

Hy-B CHISLETT, M. S., and BJÖRHEDEN. O.

Influence of Ship Speed

on the Effectiveness of a

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Lateral-Thrust Unit

Hy-9 BARDARSON, H. R.. WAGNER SMITT, L., and

The Effect of Rudder Configuration on Turning Ability of Trawler Forms.

20,00

CHISLETT, M. S. Model and Full-Scale tests with special Reference to a Conversion to Purse-Seiners

Hy-lO WAGNER SMITt, L. The Reversed Spiral Test. 10,00

A Note on Bech's Spiral Test

and sorne Unexpected Results

of its Applications to Coasters

HYDRO- 0G AERODYNAMISK LABORATORIUM

is a self-supporting institution, established to carry out experiments for industry and to conduct research in the fields of Hydro- anti Aerodynamics. According to its by-laws, confirmed by His Majesty the King of Denmark, it is governed by a council of eleven members, six of which are elected by the Danish Government and by research organizations, and five by the shipbuilding industry.

Research reports are published in English in Iwo series: Serles Hy (blue) from the Hydrodynamics SecliOn and Serles A (green) from the Aerodynamics Section.

The reports are on sale through the Danish Technical Press at the prices stated below. Research institutions within the fields of Hydro- and Aerodynamics and public technical libraries may, however, as a rule obtain the reports free of charge on application to the Laboratory.

1-IYDRO- 0G AJR0DYNAMISK

LABORATORIUM

Lyngby - Denmark

Wind Tunnel Tests

in the Field of -.

Industrial Aerodynamics

by

Henrik Ditlev Jergensen

Aerodynamics Department

TABLE OP CONTENTS

Page

ABSTRACT 1

INTRODUCTION i

INSTRTThIENTATION AT THE AERODYNAMICS DEPARTIENT . ... 2

APPLICATIONS OF TRE HyA WIND TUNNELS 7

SmOke Tests with Ship Funnels 9

Results of Actual Funnel Tests 11

Smoke Tesi.s with Stacks 12

Test Techñique 14

Studies of Airfiows Around Buildings 16

Resistance and Pressure Coefficients 18

FINAL REB&ARKS 22

-1-ABSTRACT

A general description of the HyA wind tunnels

and measuring equipment is given. Some testing procedures

within the field of industrial aerodynamics are described

in detail and general results presented. Applications of low speed wind tunnels within the fields of civil engineering and naval architecture are discussed.

INTRODUCTION

The Aerodynamics Department at the Hydro- and Aerodynamics Laboratory was mainly built to cover a requirement in Denmark for research and development within the field of industrial

aero-dynamics.

Because of the close connection to the Hydrodynmics De-partment, the Aerodynamics Department bas performed many tests in

the naval architecture field, which is quite unusual for

aero-dymi ce laboratories.

Besides the more special tests the laboratory has

de-veloped standard tests which are used both by Danish and foreign

customers. Up to now customers from seven different countries

bave used the HyA wind-tunnels.

The purpose of this publication is to describe some of

the technical installations and some standard tests which can

-2-Figure 1.

View of the open circuit tunnel with the test section.

The transverse area is 1.14 x 1.14 n and maximum speed

about 14 rn/s. In the background is seen a number of waterline models usedfor smoke tests.

INSTRUMENTATION AT THE AEEODYNAMICS DEPART1VTTNT

The Aerodynpmics Department has to-day two wind tunnels

for aerodynamic low-speed tests. One is an open-circuit tunnel, where the air is sucked through the test section. A picture of

this tunnel is seen on Fig. i and a plan on Fig. 2a. The tunnel

is a modified version of the one used by the late Professor Nøk-ken6ved and his colleagues in their pioneer work at the Technical

University of Dennir on wind pressures on buildings (Ref. 2).

The other is a single-return wind-tunnel designed by Professor N. Holm Johannesen, Manchester University. Fig. 2b shows a plan of

this tunnel, and Fig. ₃ shows a picture of the test section. The, test section in the open-circuit tunnel has a trans-verse area of 1.14 n x 1.14 m and is about 4 n long. The inlet

part is about 10 n long, and the maximum air speed in the tunnel

is about 14 ni/s. One of the side walls is made of glass over a length of 2.74 m, so that there are very good possibilities o±

AIR INTA}ÇE

3X0

HONEYCOMB

18800

KMEtAL TIIRMNr, YAWS

737 I.ETAL TURNING VANES

INLET GECTION

3 AXED DIFFUSER SCREEN

2 REI.KIVABLE SCREENS PANE (W GLASS, A WORKING SEETION 7 STRAIXHTENERS V.VRRN6 SGCT88N 2688 A

8 BLADE FAN O PRE-ROIATIONS' VANES

(y --i

:1

Plan of open-circuit tunnel.

Figure 2b.

Plan of closed-circuit tunnel.

WORD-LEONARD GENERATOR (88KW AIR OUTLET 24 NETAL TURNING

4-

_ALTUt

-4

:H-Pigure 3.

View of the test section and entrance cone

of the closed circuit tunnel. Contraction ratio 13:1, transverse area 0.7 x 1.0 m

and maximum air speed 30 rn/s.

The flow pictures are made visible by means of paraffin-oil vapour or lycopodium powder. The speed in the tunnel can be

varied continuously through a Ward-Leonard system and is

mea-sured by a pitot tube. Purthermore a titration-aggregate for

measuring concentrations in the air flow is available.

Different boundary layers can be developed in the test

section when the roughness of the inlet part of the tunnel is varied. Experiments with ship models are carried owt with a

boundary layer corresponding. to that of the open sea, see Fig. 9, while for civil eng.ineering problems the boundary layers are

made to correspond to those over landscapes and cities by

ex-tension of the models into the inlet section.

The transverse area of the working section of the closed-circuit tunnel is 100 x 70 cm. The longest dimension is .normally

arranged horizontally, but may be turned to a vertical position.

Thé air velocity can be varied from 0-80 rn/s.

The flow in the tunnel is characterized by an entrance

cone with a high contraction ratio, 13:1, and by use of five

turbulence-reducing screens installed just before the entrance

rc:

5

small ones,, which disappear more easily. This design ensures a highly uniform flow field of low turbulence in the test section,

s S

Figure 4.

Calibration set-up for the four-component balance

designed by C.Aage, Ref. 7. In front of the

manoeuvring board is seen the strain-gauge

bridge equipment.

o e a

Figure 5.

The revolving four-component balance mounted on the top of the test section and connected to the recording

instruments. The model can be seen through the

-6-Pigure 6.

The model from Fig. 5 mounted upside down in

the working section ready for measurements.

where the average speed is measured by a venturimeter. The natural boundary layer in the working section is about five mia,

but it is possible to create a thicker boundary layer when

needed.

Por this tunnel some special measuring instruments have been built, such as a V-shaped 3-component balance for measuring

lift, drag and moment in the middle of the tunnel. In addition a revolving 4-component balance for measuring lift and moment

about two axes is available. This instrument is designed by

Ç. Aage (Ref. 7) and is especially used for surface-bodies. Pig. 4 shows the calibration set-up, and Pig. 5 shows the revolving table

and the dynamometer placed on the ceiling of the working section.

The model, which is placed upside down, can be seen through the

plexiglass on Pig. 5, and directly on Pig. 6. Finally two

1-component balances for the same purpose are at disposal. The 4-component balance is .based on a strain-gauge measurement, while the others work by means of differential transformers.

A hot-wire anemometer and a set of ordinary manometers for measuring low pressures about one mm of water are used in

both tunnels. A multimanoineter carrying 36 pressures at the same time has recently been designed and manufactured. The range of

7

Figure 7.

36-hole multimanonieter.

the manometer varies from O-700 inni of water and the readings can be taken photographically. The instrument is shown on Pig. 7.

Most of the data reduction work is done on the HyA-GIER

computer, which saves time and avoids errors. Several programs

are now in operation such as calibration and analysis of the

4-component balance readings, calculation of pressure coefficients

from the multimanometer measurements, calculation of relative wind angles and corresponding manometer settings for ship smoke

tests, and calculation of effective stack heights.

APPLICATIONS OF THE HYA WIND TUNNELS

The open-circuit tunnel is mainly used for study of flows with special reference to stacks, ship fumiels and flows around

buildings. The closed-circuit tunnel is more suited for

deter-mination of resistance coefficients for 2-dimensional as well as

3-dimensional bodies, e.g. ship superstructures, buildings, bridges, towers and roofs. Purthermore the tunnel is well

equipped for calibration of all sorts of air-velocity measuring instruments such as cup meters, hot-wire instruments, ventilators and fans.

I

-8-Pigure 8.

Photos showing the model of a fishing boat

rolling over the ground.

Also unusual aerodynamic problems have been solved in the

tunnels. Some examples are briefly quoted:

A motor boat which was hauled ashore and lying on compara-tively smooth rock, was lifted by the wind and rolled on the cliff

through a distance of 43 n. This observation was used to

deter-mine the wind speed which was important in a law case regarding a

building under construction damaged during this gale. Pig. 8 shows

four pictures of the rolling boat, and the results of the experi-ments corresponded well with observations of wind force made by

neighbouring meteorological stations.

An architect designing a summer house on a hill overlooking

the sea desired to choose by means of experiments the best possible

position for a barbecue, taking into account the prevailing wind con-ditions.and studying the influence of different roof types and of

screemings and hedges.

Also smaller objects such as street light fixtures have

been tested for minimum air resistance.

In the following a number of typidal tests are described in

-9

Smoke Tests with Ship Funnels

Ship funnels "have often been designed on a purely

esthetic bais with no regard being paid to the aerOdynamics of the outlets from the funnel.' -in sucb cases pasengers and

crews have complained about smpke' deflectiofl on. dek and in the ventilation system. Even a slight. down-draught of smoke is unpleasant on account of the sulphur content of the sinke.

Therefore a need for studies with a view to avoidingthese

smoke problems has arisen. Over the years a standard test for examination of an actual funnel has been developed at the Aero-dynamic s Department.

This standard test is a model test to the scale of 1:100

made in the open-circuit wind-tunnel using a waterline model in

different load conditions. Pig. 1 shows models of 'this type.

As a standard are used wind speeds corresponding to 2, 5 and 8

Beauíort in connection with the absolute wind directions 00,

o o o o .

45 , 90 , 135 and 180 from the bow. In this way it is possible

to obtain a complete picture of the aerodynamic behaviour of the

ship funnel.

The boundary layer corresponding to that of the natural wind over open sea is weil known and has often been described

in the literature. By use of a system of small blocks o wood in the inlet section of the tunnel, this type of boundary layer is produced at the position of

the model. Pig. 9 shows an ex-ample of such a measurement. When using a scaled model and the boundary layer, as de-scribed above, it only remains

150 VELOCITY PRILE , VELOCITY PROFiLE

to keep the ratio between the

o

I

velocity, V, the same for

mo-/

dei and ship in order to ful- 50

fil the model laws. It is

o

then possible to compare the O

smoke distribution around the

model funnel with that of the

ship.

/

Q5

Pigure 9.

Wind velocity profile of the open sea.

s

b

Figure 10.

Funnel with poor aerodynamic behaviour. Smoke

occurs on the aft deck, the funnel top is not free of smoke and both funnel and mast

will turn black. lo

-Figure 11.

Funnel for the same ship as in Fig. 10. The funnel is higher, narrower and shorter in the

longitudinal direction. The smoke is

clear of the funnel top, mast and

The smoke is produced by boiling paraffin oil, and the

paraffin vapour is then dissipated through the funnel in the

wind tunnel at the desired S/V-ratio. _{The speed is measured by} a venturimeter, inserted in the air-flow before the oiL-vapour' is added0 _{As the paraffin vapour is white, the smoke plume is} clearly visible against a black background and _{easy to} photo-graph. 1±' the film is exposed for 30 sec., the picture will

show a diffuse haze. The density of this haze indicates the

smoke concentration and forms the basis of an estimation o± the

smoke deflection. The smoke can also be filmed,, as the

moving-picture more clearly shows the different vortices around _the

funnel. The best impression of the flow picture is, however, ob-tained by direct observation of the tests. _{Figs. 10 and 11 show} two smoke pictures.

In order to determine the turbulent _{zone of the ship,}

smoke is dissipated in the wind-tunnel ahead of the ship. Ín

this way the height of the funnel can be estimated _{so that the} funnel top penetrates the turbulent _{zone. Furthermore it can be}

seen whether the superstructure has any effect on the flow from

the exhaust pipes. _{The funnel top has to be clear of the vortice} made by the superstructure in the windward side.' As the picture from these tests generally are not very descriptive, _{a direct} observation is necessary.

Results of Actual Funnel Tests

Smoke on deck is most pronounced for relative wind direc-tions of 45-100° from the bow. A funnel with low-aspect' ratios of the horizontal sections will have less tendency to suck down t'he smoke along the lee side of the

funnel

Yind tunnel experiments indicate clearly that this feature

is undesirable and modern designers have also discontinued this practice, but to avoid smoke nuisances it is essential to carry the top of the exhaust pipes up to a height which is well above

the turbulent boundary layer, which therefore must be determined for different relative wind directions. As this boundary layer is highly influenced by the position and the form of the super-structures, great improvements have in several cases' been obtained through modifications of these.

12

-In cases where a funnel is observed to have poor aero-dynamic properties, many different changes of the design may show

improvements. Below are listed the most important recommendations which according to the experience of the laboratory generally

pro-duce the best results:

i) Heightening the funnel,

Shortening the funnel in the longitudinal direction,

Letting the exhaust pipes protrude above

the normal profile of the funnel,

Slotting the funnel top to produce an air-flow

around the upper part of the exhaust pipes,

Decreasing the top area of the funnel,

Rounding the plates on top of the funnel,

Rounding the superstructures.

There. are undoubtedly other solutions to the problem.

Many designers believe that guide plates on the aft part of the

funnel contribute to raise the smoke plume. It seems, however, that these plates only are effective for certain wind directions.

Smoke Tests with Stacks

The purpose of tests with stacks of power-stations or

similar stacks delivering large volumes of smoke is to determine

the necessary height of the stack with a view to keeping the con-centration o± smelly and poisonous gases below the limit laid

down by the authorities. The most frequent gases of this kind

are sulphur dioxide SO2 and carbon monoxide CO.

The necessary height of the stack is therefore dependent

on the 502 and the CO percentage of the smoke, the smoke quantity,

the smoke speed and temperature, the ground roughness and the

weather conditions.

To study this problem landscape models are manufactured

from a map scaled to model size and with a contour line spacing

13

-long and have a width of 1.14 m corresponding to the width of

the tunnel. The model stacks are made of stainless steel pipes. The sizrrounding buildingsare made of small wooden blocks.

Single trees and bushes are normally not reproduced in landscape

models.

The model scale which normally varies between 1:250 and 1:1000, depends on the height of the designed stack and on its inside diameter, as for practical reasons the diameter of the

model stack should not be less than 2 mm. The scale depends

further on the distance from the stack to objects of speeial in-terest in the surroundings compared with the length of the test

section, which is 4 m. Such an object might be a church, a

hospi-tal, a monument, a sports ground where smoke is undesirable, or

simply the area where maximum concentration is likely to occur.

In order to ascertain that the model laws are complied

with, the following conditions must be satisfied:

i) The wind velocity profile and the degree of turbulence to be identical for model-and full-scale at the position of the stack.

2) The ratio between smoke- and wind speed to

be equal for model- and full-scale.

The temperature differences between the smoke and the

surrou.nding air and the temperature gradients in the latter are

normally neglected for reasons o± simplicity, but empirical

cor-rections for these phenomena are applied.

The actual full scale wind velocity profile and degree of turbulence at the site where the stack is to be built can be

de-termined only by very expensive and difficult. boundary layer measurements. In most cases approximate data derived from

sta-tistics are therefore used.

The long ini.et section of the tunnel creates a natural boundary layer over the up-wind part of the model. The wind ve-locity gradient and the degree of turbulence òf the boundary laye]

is then changed by varying the rougbness of the tunnel floor in front of the model to such à degree that within a reasonable

-loo

5'

o

o

14

-equal to that estimated for full scale. Pig. 12 shows a dia-gram of four velocity profiles over a model of a city in four

directions from the stack. It is not possible to keep the

Rey-nolds' number constant for model and full scale, but owing to

the sharp-edged models there will be no appreciable Reynolds' effect on the test results.

25W -w Q 20' I- :1' x150

I

'I

J'

I

_--'

Diagram of four velocity profiles over a model of a city in four

directions from the stack.

Test Technique

The tests are normally evaluated both visually and

quan-titatively. In the visual test paraffin vapour is used as smoke

and its speed is controlled by a venturinieter. This white smoke

is clearly visible, and excellent photographs can be taken of

the passage of the smoke over the model. Pig. 13 shows a plume over a town with a few tall buildings.

By varying the stack height and the S/V-ratio it is possible to observe where the smoke deflections occur under

different conditions. Also vortices around large buildings can

be studied. The results are used for planning the quantitative

tests, which are more laborious.

In the quantitative part o1 the experiments a 100% IH3 smoke in measured doses is dissipated and the ammonia

concen-tration determined at a number of selected points on the model.

-a

Figure 13.

Smoke plu.me.over a model of a town at four different s/v ratios.

order to avoid disturbance of the flow field. The samples are then analyzed by titration. _{The local concentrations are}

fi-nally mapped out for each test Condition.

As previously mentioned no

attempt is made to ensure the _____ correct smoke témperature.

Nu-merous full scale measurements have shown that the smoke plume rises considerably, due to its temperature being higher than

that of the atmosphere. _{In the} experiments this rise is

obtai-ned by means of an increased

height of the stack. The height of the model stack, _{HMODEL, is}

made to exceed the designed

15 -H,DEL y r1 A I y h H UI WARM A HFF Figure 14.

Relation between the effec-tive stack height and

16

-stack height, H, by a calculated plume rise derived from the

formula (Ref..5) given by Stüeinke:

4.86. 1O3!QsMoTsMo

O. 1O5.1O4QsMo(TsMo_TU)

=

V

where

H is the plume rise in m,

SMOKE is the total rate of release of smoke in

Nm3/h,

TOKE

exit

Tu is the ambient air temperature in °K,

V is the average wind speed in m/s, and

S is the smoke exit velocity in zn/s.

Fig. 14 shows the relation between the designed stack

height H and the effective height

The height of the designed stack is now given by the

expresSiOn:

H ₌ HMQDEL -k

(H-ll)

where the average wind speed, V, is determined from the velocity

profile at the height H + H, and where k is a safety-factor

which can be included according to the irregular atmospheric

con-ditions. At HyA a value of k = i is used.

In case the influence on the smoke concentration of a tall building in the immediate neighbourhood of the stack is wanted,

the plume rise correction is neglected and the model stack height

is scaled directly from the designed stack, as this effect has no essential dependency Ofl temperature.

Studies of Airfiows around

The HyA open-circuit

tunnel bas in

cases been used

to study flows in- and outside buildings. Due to the fact that

little attention has been paid to the aerodynamic design of

buildings and structures, heavy wind may occur at places where calm air is wanted. These effects occur especially at the ground

17

-around tan buildings. ..ae flow outside the buildings will

some-tinies affect the air inside through open gates, doors and windows

and cause unwanted draughts in corridors, lift shafts and

stair-cases. Some department stores want to attract the public by keeping their doors wide open and to protect the inside by use

of air curtains at the entrances. Experiments have been carried

out in the wind-tunnel to determine the air speed in the entrances

as a function of the wind direction and lee-wall dimensions. The

previously described model laws for sharp-edged structures also apply in this case; it is thus possible to consider alternatives

and compare the air speed measurements relatively. These

measure-ments have been taken with a hot-wire anemometer, as this sort of equipment is better suited for low speed measurements than a

pitot tube.

Flows around buildings can be made visible by means of

smoke as well as lycopodium powder. The latter has been used in

cases where snow drifting and. wind vorticity in the surroundings of the building have been studied. Fig. 15 shows a semicircular sixteen storey apartment house, where the results of the test

were useful to the landscape gardeners.

EE

-

--w

A model of an apartment house, where the lee

18

-Resistance and Pressure Coefficients

Resistance coefficients, CT, or pressure coefficients, C, are determined by means of measurements carried out in the

closed-circuit tunnel with, homogeneous velocity field. Both two- and three-dimensional bodies have been tested.

F'= CT *?V2 A

where

j 2

; p=CfV

H.

24'

the air density in, kp s /m , the tunnel speed in m/s,

A = a characteristic area in m2, and

p= the loc1 pressure in

The force F is either measured by the strain-gauge

equip-nent or by the differential transformers, depending on the magni-tude and number of forces to be measured.

Determinatiòn of C for a number of points on a surface

is carried out by means of a multinianometer. The pressure holes are connected to the manometers by plastic tubes.

In case sharp-edged models are used, this kind of measure-ment will give reliable results with no Reynoldst effects.

Por use in the preliminary ship design and for ànalysis of ship trials with respect to speed and manoeuvrability it is necessary to know the total wind resistance coefficient as a

function of' different angles of attack in order to get an estimate of the wind effect. At HyA a number of' tests has been made with ship models o± different types of' ships. The models are about 50-55' cm long and made of wood. When the model is placed on a

turntable the forces can be measured as a function of the angle. Fig. 16 shows an example of a ship model used for wind

coeffi-cient measurements, and Fig. 17 shows the corresponding ;results. Another application of' the wind tunnel is the determi-nation o± the heeling moment caused by a side wind. The heeling

moment may be considerable for ships with large superstructures

and must be taken into account when judging the transverse

sta-bility. As wind fdrces. cannot normally be applied directly to models tested in tkLe towing tank, the results of the wind tunnel

Figure 16.

Ship model of a ferry-boat for wind coefficient

measurements.

200 40 .10 90 100° 1'° 140° 160 1800

-

-200 400 60 80° 1000 ₁₂₀ 1400 1. 18l°

Figure 17.

Curves of non-dimensional resistance and moment

coeffi-cients for the model shown on Pig. 16 define as:

Longitudinal resistance coeff. Transverse resistance coeff. Yaw moment coeff.

Roll moment coeff.

2 2 c

PJ2

20

-tests are used for calculating the heel to which the models are to be inclined, in order to simulate the behaviour of the ship under wind pressure.

Pressure and resistance measurements have also been

per-formed in the wind. tunnel with models corresponding to the

under-water part of ships in order to get a check on similar

measure-ments taken in the towing tank. These tests are directly compa-rable as the Reynoldst numbers in the closed tunnel and in the towing tank are of the saine order of magnitude.

Predictions of ship propulsion in rough weather are

based partly on results from seakeeping tests in the ship model

basin and partly on wind resistance tests, as described above.

Under these conditions the wind resistance is in many cases of

the same order of magnitude as the seakeeping resistance. The

wind horsepower for a fast cargoliner sailing in a strong breeze

about 6 Beaufort is of the order of 2000 liP.

Figure 18.

Pressure hole distribution at balcony arrangement at the end wall of an

21

-I

Figure 19.

Model of a hangar for wind load testing.

Other applications of pressure coefficient measurements are for example determination of the wind loads on roofs in cases where the wind load regulations do not give sufficient

in-formation about a safe solution, _{In some cases the regulations}

would seem to give too conservative figures, and test results

may thus reduce the cost of the construction.

Buildings under construction, unusual roofs and balconies

are some of the examples which have been tested. Fig. 16 shows the pressure holes fixed in the outer balcony wall of an apart-ment house, and Fig. 19 shows a model of a hangar.

22

-FINAL RARKS

The purpose of this report has been to give a review of the

types of tests which recently have been performed in the HyA

wind-tunnels and to give some of the general results which have been.

obtained.

Wind tunnel testing technique has mainly been developed

to serve the aeronaitical sciences, ànd all the larger

laborato-ries have been built with these in view.

These installations are

too costly to run for a great many of the applicatioiis mentioned

in this report, and the field of industrial aerodynamics was

there-fore more or less nglected for a long period.

The building of

the HyA wind tunnels has shown an increasing demand for this field

o± research.

Although many types of experiments have been

stan-dardized by now and therefore can be carried out at relatively

low costs, further r1esearch is felt necessary before a solution

of other problems can reach a satisfactory state.

As exaxnples of the fields where research is highly needed

may be merrtioned:

Further studies of the natural wind.

Studies of turbulence and boundary layers

over lañdscapes. and cities.

Wind actions on trees and plantations.

Flows in heating and ventilating ducts..

Aerodynamic oscillations of stacks,

sky-scrapers, bridges, etc.

Aerodynamics of trains, vehicles and ships.

Aerodyninics of sails.

23

-REFERENCES

Irniinger, J.O.V. and Nøkkentved, Chi.:

"Wind-Pressure on Buildings, Experimental Researches" (First and Second Series).

Ingeniørvidenskabelige skrifter, A, No. 23 and 42, Copenhagen 1930 and 1936.

2 Nøkkentved, Chi.:

"Wind-Pressure on Building&',

International Association for Bridge and Structural Engineering, Vol. 1, pg. 365, Zurich 1932 and

Vol. 2, pg. 257, 1933-34.

3 Jensen, Martin and Franck, Niels:

"Model-Scale Tests in Turbulent Wind, Part I", Danish Technical Press, Copenhagen 1963.

4 Jensen, Martin and Franck, Niels:

"Model-Scale Tests in Turbulent Wind, Part II, Wind

Loads on Buildings",

Danish Technical Press, Copenhagen 1965.

5 CONCAWE:

"The Calculation of Atmospheric Dispersion from a Stack", The Hague, 1966.

6 Petersen, H.:

"A Type of Wind Tunnel for Simulating Phenomena in the

Natural Wind",

-AGARD Report No. 308, Paris October 1960.

7 Aage, C.:

"Licentiate Study on Wind Forces on Ships",

Technical University of Denmark, Copenhagen 1968.