\

Q

J

NBS TECHNICAL NOTE 710-9

JjATtINST. OF STAND & TECH

A111D? E3fi3ET

U.S. DEPARTMENT OF COMMERCE/ National Bureau of Standards

BUILDING

RESEARCH TRANSLATION

Discomfort Due to Wind

Near Buildings:

Aerodynamic Concepts
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards 1 was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology and facilitate their effective application for public benefit. To this end, the Bureau conducts research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and

technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to pro- mote public safety. The Bureau consists of the Institute for Basic Standards, the Institute for Materials Research, the Institute for Applied Technology, the Institute for Computer Sciences and Technology, the Office for Information Programs, and the

Office of Experimental Technology Incentives Program.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United States of a complete and consist- ent system of physical measurement; coordinates that system with measurement systems of other nations; and furnishes essential services leading to accurate and uniform physical measurements throughout the Nation's scientific community, industry, and commerce. The Institute consists of the Office of Measurement Services, and the following center and divisions: Applied Mathematics — Electricity — Mechanics — Heat — Optical Physics — Center for Radiation Research — Laboratory Astrophysics 2 — Cryogenics 2 — Electromagnetics 2 — Time and Frequency 5

. THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to improved methods of measurement, standards, and data on the properties of well-characterized materials needed by industry, commerce, educational insti- tutions, and Government; provides advisory and research services to other Government agencies; and develops, produces, and

distributes standard reference materials. The Institute consists of the Office of Standard Reference Materials, the Office of Air and Water Measurement, and the following divisions:

Analytical Chemistry — Polymers — Metallurgy — Inorganic Materials — Reactor Radiation — Physical Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides technical services developing and promoting the use of avail- able technology; cooperates with public and private organizations in developing technological standards, codes, and test methods; and provides technical advice services, and information to Government agencies and the public. The Institute consists of

the following divisions and centers: Standards Application and Analysis — Electronic Technology — Center for Consumer Product Technology: Product Systems Analysis; Product Engineering — Center for Building Technology: Structures, Materials, and Safety; Building

Environment; Technical Evaluation and Application — Center for Fire Research: Fire Science; Fire Safety Engineering.

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts research and provides technical services designed to aid Government agencies in improving cost effectiveness in the conduct of their programs through the selection, acquisition, and effective utilization of automatic data processing equipment; and serves as the principal focus wthin the executive branch for the development of Federal standards for automatic data processing equipment, techniques, and computer

languages. The Institute consist of the following divisions: Computer Services — Systems and Software — Computer Systems Engineering — Information Technology.

THE OFFICE OF EXPERIMENTAL TECHNOLOGY INCENTIVES PROGRAM seeks to affect public policy and process

to facilitate technological change in the private sector by examining and experimenting with Government policies and practices in order to identify and remove Government-related barriers and to correct inherent market imperfections that impede

the innovation process. THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination and accessibility of scientific information generated within NBS; promotes the development of the National Standard Reference Data System and a system of in- formation analysis centers dealing with the broader aspects of the National Measurement System; provides appropriate services

to ensure that the NBS staff has optimum accessibility to the scientific information of the world. The Office consists of the following organizational units:

Office of Standard Reference Data — Office of Information Activities — Office of Technical Publications — Library —

Office of International Standards — Office of International Relations.

1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted; mailing address Washington, D.C. 20234.

2 Located at Boulder, Colorado 80302.
BUILDING RESEARCH TRANSLATION

Discomfort Due to Wind Near Buildings:

Aerodynamic Concepts

J. Gandemer

Centre Scientific et Technique du Batiment

Paris, France

Translated by Information Simplified. Inc. P.O. Box 7439

Alexandria. Va. 22307

for the

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

*< °>*.

NATIONAL BUHKAJJ OF STANDABUfl S

LIBBABT FEB l 6 1981

/ o — I ' -?

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued March 1978
National Bureau of Standards Technical Note 710-9

Nat. Bur. Stand. (U.S.), Tech Note 710-9, 48 pages (Mar. 1978) CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1978

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402

Stock No. 003-003-01898-8 Price $1.60

(Add 25 percent additional for other than U.S. mailing).
Preface

The United States and Frances' Cooperative Program on Building

Technology involves an exchange of personnel and information

between the Center for Building Technology of the National

Bureau of Standards and the Centre Scientifique et Technique

du Batiment (CSTB) . Information contained in this report was selected for translation and reproduction for sale to

the building community by the Covernment Printing Office.

The CSTB papers made public through this Technical Note do

not necessarily represent the views of the National Bureau

of Standards on either policy or technical levels. Building

researchers at the National Bureau of Standards consider it

a public service to share with the U. S. building community

these insights into some of the research activities of CSTB.

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards
DISCOMFORT DUE TO WIND NEAR BUILDINGS: AERODYNAMIC CONCEPTS

J. Gandemer, Engineer at the CSTB Nantes Laboratory

Cahiers du Centre Scientifique et Technique du Batiment, No. 170,

June 1976 (Cahier 1384)

Wakes Made Visible by a Coating Method
DISCOMFORT DUE TO WIND NEAR BUILDINGS:

AERODYNAMIC CONCEPTS

J . Gandemer

1. Introduction

Flow patterns at ground level in groups of buildings result from the

complex interaction between the wind (impact, average speed distribution

with height, and turbulence) and the buildings themselves (shapes, sizes,

arrangement, etc.)

The increase in the number of very tall structures and the more or less

arbitrary, with respect to wind, installation of large structures have

frequently demonstrated the lack of adaptation of the structural environment

to wind phenomena. Manifestations at ground level, such as zones of high

speeds or eddies, make the approach to buildings uncomfortable (sometimes

even dangerous) for the pedestrian.

Elimination of these problems requires better knowledge of air flows

around structures and formulation of practical plans that the architect or city planner can use in designing larger structural units.

k

References are on page 37. Appendix I on page 38. Appendix II on pp 39-41.
This article summarizes work carried out at the CSTB institute in Nantes

in 1973 and 1974 and gives the main results of our study [1, 2].

Also, a guide was drawn up [3] which gives simple rules or practical advice

that can be used by architects and city planners.

2 . General Behavior of Wind around Structures

Flows that occur at ground level result from the complex reaction between

the wind and structural masses. The effect of structures on the flows depends

on their shape, size , and juxtaposition by establishing the distribution of

different pressure zones around the obstacles (Figs. 1-3).

Fig. 1. Geometry of "wind" flow in passing a parallelpiped obstacle.

(1) Flow line; (2) wake and vortical circulation; (3) separation point;

(4) recombining point; (5) thickening of separation limits between wake

and flow.

Fig. 2. Fluid circulation around structures of different geometries.

Generally speaking, the larger the dimensions of the structural masses (particularly height) relative to the scale of the wind (dimensions

of the gusts) , the greater their role in the shaping of the flow.
Fig. 3. Flow patterns around a building or a vertical average-rate gradient.

(1) Separation point; (2) vortical roll; (3) lateral vortical zone;

(4) vertical average-speed gradient.

As a result, every mutual positioning of these zones leads to the appearance

of flows (high pressure to low pressure)

.

On the windward face of a large obstacle the wind causes overpressure

distribution as an increasing function of height depending on the vertical

gradient of average speed. Further, a flow descends along the forward face

and upon meeting the ground forms a vortical roll (Fig. 3) ; strips of air are forced to pass around the obstacle, and in the wake starting at the separation

lines along sharp edges, low-pressure zones appear which are relatively con- stant with height and essentially related to the speed at the top of the

building. The juxtaposition of air volumes at different pressures due to

arcades, under buildings or around corners induces very rapid local flows more or less associated with violent eddies.

Finally, structural elements, by their juxtaposition, can form wind

deflectors that channel the air in narrow passages where flow is locally

accelerated.
In overall plan the shapes do not act individually, and the different

types of flow mentioned above combine in a way that depends on the properties

of the incident wind and the topography of the site. The result is therefore

particularly complex.

3. Review of Wind Properties [4-6]

Wind is a flow of air which tends to equalize different pressure zones

in the atmosphere. At low heights, it has a significant "agitation" or turbulence. Thus, at a given point the speed of the wind will fluctuate in

magnitude and direction.

The instantaneous speed of the wind at a point can be expressed by two

terms

u, (?) = u, + u; (o

where U is the average speed (for example, during a period T = 10 minutes) at a

z height z above the ground and U' (t) (a function of time) is the corresponding

fluctuation (Fig. 4).

U|t)i

to t to+T

Fig. 4. Instantaneous recording of wind.

Turbulence, i.e., fluctuation of the speed around its average value (for

the period T) , can be characterized statistically by its standard deviation,

a = l/jfe

The average speed at ground level (in the case of non-mountainous

terrain), because of friction with the ground, increases with height to a

1/ The values with a bar above are average values during a period T.
height of z (thickness of the atmospheric boundary layer) , where it becomes

constant and equal to U ("gradient speed").

G

When winds blow, the stability conditions of the atmosphere are generally

neutral. Thermal phenomena can be neglected, and the increase in the average

speed with height z ("vertical gradient of average speed") can be represented

by

u Fa = (z/zr

) a

Z Cr G

The parameters z and a depend essentially on the type of roughness encountered

G

by the wind.

Fig. 5

The standard deviation, a, in the lower layers depends essentially on,

and increases with, roughness. It decreases slowly with height,

To be able to characterize the wind completely, we have to introduce the

concept of spatial scale of turbulence (dimensions of gusts in space)

.

The dimensions of puffs or gusts of wind define the "dynamic" scale of

the latter (longitudinal and transverse scale) . This is a function of height

and roughness. The scale is generally determined from correlated measurements

between different points in space.
4. Criteria of Comfort

4. 1 Concept of Comfort

The speed and changing behavior of the wind affect: —The "physical" comfort of man: The forces induced by the wind vary

in time and space and act mechanically on the "human body obstacle,"

hinder his movements, disarray his clothing, etc. —"Thermal" comfort of man: Physiological heat exchange between the

human body and the ambient medium are disturbed.

These two concepts will always be subjective, because, in general, comfort

or discomfort due to the wind depends on: —The activity of the individual (comfort desired on a restaurant

terrace is different from that wanted on a pedestrian walk)

;

—The climate (in some latitudes we may even want an increase in some

of the wind effects such as natural ventilation) and the season,

depending partly on the garments worn; —Meteorological conditions (temperature, precipitation, sunlight,

humidity, etc. )

;

—Physical (e.g. age) and psychological state of the individual.

The Beaufort scale (Table 1) gives some information on the manifestations

of wind as a function of speed and the sensations felt.

Table 1. Beaufort Scale

Wind speed, m/sec

Force z = 2 m Wind characteristics

2 1.5-3 The face feels the sensation of the wind

Leaves rustle

3 3-4.5 Leaves and small twigs in continual movement

Wind unfurls flags constantly

Hair is disarranged and loose clothes blow in the wind

Dust and papers are lifted

Branches are shaken and hair is very much blown about

Small trees and their leaves are blown about and walk

is affected slightly

Large branches are put in motion and the wind makes

telephone wires sing; umbrellas are used with difficulty and walking becomes very much affected

11-14 Trees are in constant movement and there is great

difficulty in walking against the wind

4 4.5-7

5 7-9

6 9-11
Table 1 continued

Wind speed, m/sec

Force z = 2 m Wind characteristics __

8 14-17 Tree branches break

In general, pedestrian movement is very difficult and

dangerous

9* 17-20 Risk of violent throwing to the ground as a result of

squalls

*The concept of comfort is not the same as that of safety. The danger

threshold which corresponds to the force which tends to throw one to the

ground is based entirely on mechanical and aerodynamic considerations

(balance, weight, position, etc.) and in general corresponds to speeds of some 15 m/sec.

The definition of a criterion of comfort is thus a difficult problem

and it seems improbable if not impossible that a single criterion can be

introduced that can be universally used for all effects cited above.

At the present state of our knowledge, observations and experiments

made on site and in the laboratory indicate the basic role played by

speed and turbulence in human comfort. —— When the wind blows it creates a force (proportional to the square

of the speed) which affects the pedestrian and he overcomes it or compensates by his bearing. The higher the wind speed, the more he

will have to fight the wind and the greater will be the discomfort.

The discomfort is directly related then to the level of the force

due to the wind and will be characterized by the modulus of the

average speed, If, The wind (or flows induced between structures) is a variable

magnitude: — The wind varies from one point to another. It is sufficient to move around within a tall group to see the coexistence of very

calm zones with zones of rapid flow or even of strong

turbulence; hence strong horizontal gradients exist.

Strong horizontal speed gradients [characterized by the ratio

(U- - !L)Ay] are reflected in a large change in speed moduli in very

little space (example: at the corners of tall buildings).
The higher the ratio, the more rapidly the pedestrian must adapt himself

and the more the discomfort increases (Fig. 6).

Fig. 6

The wind varies in time; Thus, even when standing still, the pedestrian,

considering the phenomenon of wind gusts, will be subjected to a flow

(and thus a force) which varies in intensity and direction with time.

This property of variability or instantaneousness makes it necessary

for the pedestrian to constantly adapt himself, to a new situation and causes the main discomfort in walking and maintaining equilibrium, the disarrangement of clothing and hair, the use of an umbrella, etc. The

turbulence level of a flow, a, characterizes the concept of wind

variability.

As a result, for our criterion of comfort as well as the adjustments

required or even for practical advice, we take into account only the

discomfort due directly to the "wind phenomenon." This is characterized

locally by the average speed and turbulence. Other aspects such as the

ambient temperature, the psychology of the individual, etc. are not included in our criteria.
Nevertheless, the comfort criterion will be associated with the local

climate in the form of a discomfort frequency (number of times the discomfort

threshold is exceeded in relation to the season, the wind direction, etc.) at

each point on the overall plan.

4.2 Descriptive Parameter for the Discomfort due to Wind [7-13]

Available quantitative data on comfort are definitely not sufficient and

additional studies are needed. However, considering the importance (see

section above) of the average speed (U) and turbulence (standard deviation

O = >/u % 2

)

, we suggest characterizing the speed field locally by the

simplest possible grouping, U + a. It should be mentioned that recent work done by J. C. Hunt [11] indicates

the preponderant role of turbulence as compared to average speed in the effect on human comfort. J. C. Hunt [10] proposes the grouping U + 3cr. Recently,

A. G. Davenport [12] suggested U + 1.5a

For the present we are using the simple grouping U + a, but it should be

noted that our results will be easily transposable if in the future it seems

that a more "refined" combination should be adopted between the average

rate and the deviation.

In wind tunnels the grouping U + O (which corresponds to a flow at

ground level or on a balcony) can be expressed adimensionally in the form

of the comfort parameter, ty (at height z ),

4, = u + a

r r

where U and O are the average speed and standard deviation at the

reference point, defined at the same height as that of the measurements U

and a but without the structures (Fig. 7).

Reference U

Fig, 7
NOTE: The direction of the flow relative to pedestrians has an especially

critical effect when the flow is ascending (with transport of aerosols).

Strong horizontal speed gradients have a showy effect on pedestrian

discomfort, essentially if the pedestrian is moving.

These particular phenomena are not included directly in our comfort

parameter but are specified in the study of "aerodynamic anomalies"

(Sect. 7).

4. 3 Comfort Threshold - Discomfort Frequency

4.31 Comfort Threshold

When the discomfort threshold is introduced, the values commonly

assumed are the following:

U ,< 5 m/sec - start of unpleasant manifestations such as raising of

dust, irritation of the eyes, disarray of hair, etc. and with a standard

deviation of a = -/U'

2

, corresponding to that at ground level in open

country and which is related to the average local speed by

a - 0.2 U

The comfort condition to be observed is then written

U + a >^ 6 m/sec

4.32 Concept of Discomfort Frequency

A discomfort threshold by itself has no meaning if we do not relate it

to the frequency of discomfort, that is, the percentage of the time that

the threshold is reached or surpassed. Depending on the different activity

zones in an overall plan, the acceptability or nonacceptability of a given

frequency differs. One can readily tolerate locally a surpassing of the

threshold for 50% of the time, e.g., if the zone in question is not

accessible to pedestrians (automobile access corridor, etc.), while on the

10
other hand we would want a discomfort frequency of no more than a few percent

on a restaurant terrace. The designer thus plays the most important part in

this choice.

4.33 Calculation of the Discomfort Frequency

We mentioned above that the local discomfort in a building grouping is

expressed as the frequency with which the discomfort threshold is exceeded.

This necessitates a series of measurements on site, which consists in "calibrating" the site with respect to the meteorology station and a study in a wind tunnel, for example, in order to obtain locally the parameters of comfort

(ijj or a similar form) which allows finding the discomfort frequencies.

First Phase. Comparison of the site with the nearby meteorology

station, which is assumed to be representative (Fig. 8)

^"^l*. 0,14 (met. sta.)

U 10 met. sta.

site

Fig. 8

The simultaneous measurement of the wind at the site and the station at z o and at 10 m allows determining experimentally the coefficient of correlation, k. This can be estimated theoretically (see Appendix 1) , but it is much preferable

to measure it. _

U Zo site - kU ^ met. eta.

The height z is any relative height and is adapted as well as possible

to the nearby environment so that the measurements made are meaningful.

Maintaining the reference speed U defined above, we obtain

\] r = k(z r /z )Uio .„ r l u met. sta.

where a [see Fig. 8] is the exponent of the vertical gradient at the site.

11
The parameter of comfort, ip, takes the form

U + a + =

k \ 7 I U10 m<H&> (1 + 'r) V-ol **v.X. where 1 = a /U , the intensity of the turbulence at the reference point

measured experimentally (on the ground or in a wind tunnel, for example).

Second Phase. Laboratory Study

We have seen that the dimensionless ^ values can be obtained in the

laboratory provided that the simulated wind has, at the scale of the model

and depending on the wind direction, the static and dynamic properties that

prevail at the site, and provided that the nearby environment is taken into

account.

Third Phase. Presentation of Results of Discomfort Frequency

The statistical data from the nearby meteorology station are expressed

in terms of speeds Uio with annual frequencies below the threshold.

meteo ^ (The below-threshold frequencies may be broken down according to the

season, the hour, the day, the wind direction, etc.)

T3 /"*

\

ti C Tl/S 3 O 25 O -H "

U -U W) cd 4J

0) CO

«d 20-

cu u

> -H O toO ,a O

CO H

O

6 U 15. O O (U

CD -a e

0) ^s

CDaCO

a)oo

CtJ

CD5

6o

IP

10

>) \

— ^

•

•— ^

?

j/^

\ *^

I

i

I

I !

I

I

I

^ \

\

I

I

!

1—¥

0,1 1 5 10 20 30 40 50 60 70 80 90 95 97 98

Below-Threshold frequency (%)

99 99,5 99 7 99,8 99.9

Fig. 9. Example of statistical data for three meteorological stations, all

wind directions together

**Note: meteo ref. meteorological station (also met. sta.)

12
Example:

The Uio =10 ra/sec speed at the meteorology station of: meteo bJ —Strasbourg will not be exceeded 99% of the time, and will thus equal

this or more 1% of the time; —Lille will be exceeded 4% of the time; —Marignane will be exceeded 13% of the time.

The discomfort threshold is such that U + O = 6 m/sec, and therefore such that

TT =

6

ul o meteo y —

k(z r /z ) a (1+V^j

If locally, at point j on a general plan the comfort parameter is iJj . , the

local frequency for exceeding the discomfort threshold (1 - F.) will be

obtained graphically from the statistical data for

U, i° meteo

k(z r /z )a (1+Ar)^

Thus, this procedure permits relating the adimensional comfort parameter at

each site to the point considered. This frequency can also be weighted as a function of weather (season, etc.), the predominant wind directions, and the

roughness around the site.

5. Overview of the Studies

5.1 Progress of the Study Made at CSTB

The wind-tunnel studies simulating the natural wind of the velocity field

in a particular spatial plan allow its optimization, taking into account

knowledge of the neighboring environment, prevailing winds, etc. but the

solutions proposed are not generalizable to other cases, being too specific

and too detailed. However, all progress in studying the "school case,"

where the anomaly is simplified, isolated, and extracted from its practical context , does indeed make it possible to discover the parameters

which can enter into the quantification of the anomaly, but it represents

an approach that is much too theoretical to be generalizable.

The study made at the CSTB Nantes Facility is viewed entirely differently

from the studies mentioned above.

We started with standardized spatial plans in sufficient number, representing existing or proposed structures, and subjected them to different wind

directions with different types of wind, measuring the characteristics of the

velocity field. Then we tried to explain statistically the correlations

between the high or low values of \p and the geometry, the arrangement of the

buildings, etc. , and finally the means of controlling 4).

13
It should be remembered that the effects or anomalies presented below

are not isolated cases but were obtained as the result of general behavior

patterns seen in realistic structural environments. It is evident that a study taking into account the topography, the wind force distribution, direction, etc. of a particular spatial plan would lead to a high level of information detail, higher than that we gave, since only the general flow patterns

are given here with the order of magnitude of the discomfort.

5.2 Choice of Spatial Plans

In order to be as realistic as possible, our study was made in collaboration with CRMAA architects (CRMAA = Centre de Recherches Methodologiques

d' Architecture et d ' Amenagement) , especially with regard to the choice of

spatial plans, because of their being representative of contemporary and

future construction methods.

Twelve spatial plans were finally selected, taking into account their

aerodynamic interest, namely —The ease of "reading the aerodynamic phenomena," —The unity of the spatial plan over a sufficient area (300 x 500 m)

,

—The "flattest" topography possible,

•—The average height of the tallest structures, —The maximum density of the most typical aerodynamic anomalies, —The least known aerodynamic shapes.

We can cite, as an example, the classes of construction in "rows,"

in "cells," on "piers," in pyramids or disconnected, in old structural

milieux, in groups of tall buildings, of rounded shape, etc. (see the cover photo and the photos below)

.

14
Spatial Plans

Inrows

In

units

15
* >-«-/- , wf ,'. W*>#*3W «j 4 >#*

'•'•<•,;

,

II £

i a

, *."t- vv

I ^P*; ... '.-V . '^*>

"' 1

^W&

' -' Tl V | ^ -a, / . ^ ^jj -« /*.

T

X

•

m

On piers

Group of

tall

buildings

16
\ ' •' ' ''

. -' ' *%***.

';'.•; 'i"',, 1- -':'/ ^Si : **^^ \

k

-..' '

. 1

r'

.._ . ^J

1

" V...,

^RSfy^* iv 1 pi •C^^s

M

' TrSyac-„

'' m^Sm$9 r^iBS^^ie*1 *^^''*' - *^Mr T'f**

H^«r»««i^.,

- ^^.Z^^imk. •- JMI|| *£&&

F^k^B

jff'-lj

B^'JSJSJ * --SrpSftSft «\

1* 'J'laH

Pyramids

Rounded

shapes

17
Not connected

Old structural

environment

18
1 2.3

. $/

2,0. /

/

m~ 1.5 - o

•"1,0

'//

/

0.5.

V /

/

0.

Fig. 10 a

0,5 1,0 1,5

«f («• 0,16)

2,0

t

-Pi- 2 - 9- 5 E o s H -S ,.

H-1 c '.5, 3 S C o |

. •>*

*j => 1 • 1 ^

C -<u . o >^\

0.5 . • ** ^"

. <^—. , j , » 0.5 Fig. 10 b

0.5 Fig. 10 c1,0 1.5 f [«« 0, 16)

-P<<

1.5 2,5)

3,5'

3.0

7

2.5

2

/' • .

a~ 1.5

<»-

1 0.

• /

/

0.5

.

I /

1 1+ 2.5

Fig 10 Graphical correlation of the parameter (J> obtained for (a) wind

in a suburb and wind in open country; (b) wind in a suburb and wxth

uniform flow; (c) wind in the city and wind in the open country.

19
6. Experimental Study

6.1 Importance of Good Reproduction of Wind in a Wind Tunnel;

Effect of Gradient

We know the determining role of the average-speed vertical gradient

which fixes the distribution of pressure around obstacles [4] and there

establishes the flows. We also know the role of turbulence, which tends

to reshape the separated flow by widening the wake (Fig. 1) and which by its

level (intensity of turbulence) or size (scale of turbulence) partly governs

the development of turbulence in the wakes.

By way of example and to show the importance of good reproduction of the

wind phenomenon, we subjected the same spatial plan with the same incidence

to four flows—a flow as uniform as possible, and three flows reproducing

to scale the winds of open country ( a ~ 0.16), suburbs (a - 0.25), and city (V-0.41)

(The corresponding gradients were measured in the presence of the model.)

If we set the ratio

r _ + a _ U (1 +fc)

V Ur Ur where £ = cr/U, the intensity of the turbulence (at the reference level)

,

and if we study the correlation (for the same points on a spatial plan)

between the values of cf> and £ obtained for wind of the suburban type and

uniform flow, we find that (Figs. 10 and 11) the values of (j> are greatly

undervalued in uniform flow (on an average, undervalued some 100%), and

the same is true for turbulence (some 30%) . This latter point shows the

role of turbulence upstream on the properties of the velocity field.

Further, by observing the relatively high dispersion of the measurement

points (especially H) , it seems extremely difficult, and more than one can expect, to draw quantitative conclusions about the velocity fields in a group of buildings if the wind tunnel used does not correctly reproduce

the static properties (gradient) and the dynamic properties (turbulence)

of natural wind.

Correlations between the values of <J> and 1 obtained for wind in open

country and wind in a suburb or city (Fig. 10) show the very marked

effect of roughness (exponent a) on the factor <j). The role of the

exponent a relative to turbulence is less marked (Fig. 11), but the

20
»0,50

•HU

i

«. f 5om | c&S X

S 1

' / j-j = O co,5. /

•HG

Q>§

• //

& 2

*

• /L. '

_, 0. >

0,50

'_ Ccmpogna ( « = 0, 16) 0,5

(<* = 0,25) Country

Fig. 11. Graphical correlations of parameter £ obtained for wind in the

city, in the suburbs, and in open country.

dispersion of the points is still high, which emphasizes the importance of

upstream turbulence relative to the velocity field.

The parameter (J), defined above, is equally sensitive to a but less so than <f>, taking into account of the fact that the intensity of the

turbulence, £ , increases with the roughness.

In conclusion, it appears essential to reproduce in the wind tunnel

as closely as possible the natural wind at the scale of the models. Therefore the standard aerodynamic wind tunnels (regular, uniform flow) cannot

properly be used except for essentially qualitative purposes. It should be

noted that if we want to use the results obtained in a wind tunnel in an actual case and use them very correctly, the "particular" properties of the

wind corresponding to the site studied must be reproduced exactly.

IMPORTANT NOTE: The overall plan studied shows the average heights of

buildings between 15 and 35 meters high. If we assume that around a height of 40 meters we eliminate some of the roughness effect, we can find

the parameter

U(l + I)

<f> = =

Ui»o site

where the velocity u\o is the average velocity obtained at a height of 40 m

above the site.

21
We find that for an average of the measurement points, the parameter $.avg.

is practically the same for our different types of flow:

4>*avg = <f> (Z /40) a

* avg . r

As a result the same average wind at 40 m from the ground produces, on an average (but on an average only) the same discomfort.

It is evident that confirmation of this tendency will be needed for other

spatial plans.

This note allows us, however, to consider (Appendix 2) a weighting of the

ty values (measurements with a gradient of a = 0.16) as a function of the

upstream roughness.

6. 2 Test Conditions and Technology of Measurements

6.21 Wind Tunnel

The wind tunnel of the Nantes CSTB Facility (photo below) allows correct

simulation of the static and dynamic properties corresponding to the three

wind types with neutral stability in the scale range of 1/75 to 1/400 [1, 2, 14].

For this simulation we use several arrangements, together or not: turbulence

generator and secondary blower located at the tunnel entrance, tunnel floor

roughness, and random pulsing of the average flow. The purpose is to control

with the arrangements both the vertical distributions of the turbulence scale

and its intensity, and the vertical gradient of the average speed.

NOTE: In our measurements of the velocity field we used models whose scale

could vary from 1/400 to 1/200 (and therefore the corresponding wind scale).

As a result, Z varied from one test to the next but always corresponded to

a true height of 2 to 3 m relative to the pedestrian level.

Wind tunnel at

CSTB, Nantes

22
6.22 Choice of Incident Winds

We saw above how important it is to have good reproduction of the wind

properties. Therefore it was necessary to test the spatial plans for wind

in open country and in a suburb. Because of the length of the tests , we had to limit them to wind of the open-country type, this being used because

of its simplicity relative to reproduction of the environment immediately

upstream.

For all the 12 spatial plans studied for different orientations, the

exponent of the power law for the average speed gradient varied from 0.16

to 0.19 (wind of intermediate type, i.e., open country—low suburb).

NOTE: Taking into account the note appended to the preceding section, we consider in Appendix 2 an approximate correction which allows gross application for suburb winds of the values of the velocity field obtained for

"open country" wind.

6.23 Technology of Measurements

For each spatial plan studied, subjected to several wind orientations

(open country—low suburb type) we made the flows at ground level visible

by a coating method (kaolin suspended in alcohol, cover photo). Then,

taking into account the qualitative information thus obtained, we located

as judiciously as possible the anemometer probes, imposing a coordinate

grid on the spatial plan in order to obtain the local quantitative properties at all points.

The quantitative measurements were made chiefly with a hot-wire

anemometer so that with a very turbulent flow this technology somewhat

overvalues the turbulence intensity. The vertical hot wire does not

"see" the vertical components of speed when they exist. (Near the ground

we could confirm that the flow is strongly bi-dimensional and that therefore the hot-wire measurements are significant.) Hence, in the study of some aerodynamic effects we used a chronophotographic

quantitative visualization method [15].

NOTE: The model, by its presence in the experimental tunnel, forms an obstacle and modifies the flow even before it is reached ("climbing"

of the perturbations in subsonic flow) . Therefore the properties of the

flow depend on the immediate environment, upstream, lateral, or even

downstream. With regard to the zone of influence of the immediate

23
environment on the point considered, a faithful reproduction of the spatial

plan is not necessary. This can be replaced by a collection of irregular

heights of appropriate sizes, distributed in random fashion, and giving

"totally," in association with the simulation techniques discussed above,

the properties of natural wind. Therefore we have not included in our discussions the measurements made at the points where, locally, the immediate environment is not correctly reproduced along a sufficient radius

(4 to 5 times the average local heights). This is the case, for example,

of points located at the periphery of the overall plan (too close to the

wall of the tunnel)

.

7. Presentation of Results Obtained in the Wind Tunnel

In the study of different parts of spatial plans we were able to identify

several aerodynamic effects which can, in their structural context, cause

zones of discomfort or comfort relative to the wind phenomenon.

We recall that quantification of the different effects by the values

of the parameter ty correspond to an average behavior of the aerodynamic

phenomena for a wind of the open-country type and in the absence of

topography.

Row Effect

We define as a "row" a parallelepiped construction of rather small

thickness (10 m) , of a homogeneous height not exceeding 30 m (10 stories)

,

24
Break in

a row

and a minimum length of 8 times the height.

In general, the immediate environment plays a critical role only if its

height is less than that of the row or the immediate environment is not itself

a parallel row (only the first row

toward the wind then acts as a row)

.

For an incidence 6 = 45° considered

critical relative to the wind, and if

the row height is around 15 to 25 m, most of the wind will "step over" the row and spiral behind the building, creating a central zone of high speed

where the comfort parameter, ^» reaches 1.4. A way to reduce and even to

suppress the effect of the row is to arrange the rows orthogonally with one

or several built-in irregularities.

When there are openings in the rows, in orthogonal angular relation to

the wind, the comfort parameter, \\), may there reach the value 1.3 when the

width of the opening is critical, i.e. it is between 1 and 2 times the

height of the row.

Venturi Effect

The Venturi effect is a collector or funnel phenomenon created by two

structures that are not joined. The axes of the two make a right or acute

angle. The critical zone for comfort is at the neck or narrowing of the

Venturi

.

25
Aerodynamic nozzle

For a Venturi to function, its minimum

height must be greater than 15 m (h > 5 stories) . The sum of the arm lengths must

be at least 100 m, and the upstream and

downstream portions of the latter must be

"free" of all construction over an area

of the same order of magnitude as that

occupied by the collector.

When the Venturi orifice width is 2 to 3 times the average height

(critical width), the maximum flow clears the opening and, for structures

25 to 30 m high, the parameter ij; reaches 1.3 and 1.6 for buildings some

50 m high.

Curved shapes in a Venturi configuration increase the phenomenon by

their profiling, and if the collector is prolonged by a diverging element, we have essentially an aerodynamic nozzle. In the latter case, for building

heights of 50 m or so, the comfort parameter, ip, is 2.

Joining of Different Pressure Zones

Wind develops an overpressure on the upstream side of an obstacle and

a low-pressure zone behind it. For buildings arranged orthogonally to the

wind and located in fives, the different-pressure air masses connect transversally and, further, flows appear (in the direction of decreasing

pressure). This anomaly is especially important when there is a joining

corridor or a well defined canalization.

26
For the phenomenon to be clearly present, only connections such as stepped arrangements in the direction of the wind which aire the same as the average height of the structure (parallelepipeds) are critical.

This effect, the level of which is related directly to the height of

the structures, takes on importance because it is developed over a large area (close to the transverse dimensions of the groups of structures)

.

For buildings with an average height of 15 m (5 stories) , ij;..may reach

1.2, and for higher structures (10 to 11 floors) the comfort parameter is

between 1.3 and 1.6. " - In the particular case of tall towers (30 stories) , in fives and for

small displacements (0.25 times the thickness of the tower), iJj values of

about 1.8 have been obtained.

Structures with continually variable height, increasing or decreasing,

lead to formation in the back of low-pressure "trenches" which are deeper,

the higher the corresponding "rise." Therefore a flow toward the lowest

pressure zone is established.

Effect of Cells

A cell is a juxtaposition of buildings of any relative heights which

form an opening or a "pocket" (the number of sides is not limited) and

where the opening (s) of the cell do not exceed 25% of the cell perimeter.

A cell with these dimensions (relative to those of the wind) will

be totally skipped or will be penetrated by the wind (the wind "falls" into

the cell) . Therefore our quantitative approach to the effect of a cell

involves the area of the cell, S, and its average height, h (m = moyen = average) as an adimensional parameter S/h 2. Comfort inside cells has m

been taken into account ("blowpipe" phenomenon therefore eliminated)

.

The protective effect of cells is felt for heights, such as

15 m < h < 25 m, whatever the direction of the wind relative to the m

opening, so that S/h 2 <; io. The comfort parameter, ^, is thus between

0.4 and 0.8.

When h is greater than 30 m, the position of the opening relative

to the wind is important: —"Closed" cell (opening is below the wind), such that S/h l < 30,

where the average comfort parameter is 0.5 or less.

27
Configurations approximating cells

have a protective effect.

—Open cell (opening is toward the wind

or at an angle of 45°), such that

S/hm

2 < 20, where the comfort parameter is between 0.7 and 1.1 (total

movement of air at an angle of 45°).

If the opening is parallel to the

wind, the parameter ip is 1 or less

Generally, in a constructed environment any more or less well defined

cell (if its height is such that h > 4 stories) involves an increase in

comfort (sheltered zone) to the extent that this cell, even if coarse, has

transverse dimensions of 50 to 60 m. Effect of Slots under a Building

This anomaly concerns strictly "slots" at the base of a building which

connect the windward face with its overpressure to the lee face where the

pressure is lower. Practically speaking we are concerned here with

passages under buildings or with buildings on supports.

Slots under buildings are more directional relative to the wind axis

(critical angle: slot axis parallel to the wind) than full "pier walls"

(matching the width of the building), which act as "guides."

28
The higher the building, the greater the discomfort level due to the

effect of the lower pressure on the lee side. As long as the height is no greater than 5 stories, the phenomenon hardly occurs. However, for 7 stories the comfort parameter is 1.2 and reaches 1.5 for heights of 50 m

or so (16 stories) regardless of the building length. The discomfort

zone is not limited to the passages themselves but continues downstream

for a distance comparable to the size of the orifice (the air is released

in the form of a localized jet).

Diffuse

entry

Localized

exit (jet)

Guide wall

Effect of Corners

Here again the cause lies in the fact that zones of higher pressure on

the windward face and lower pressure on the sides join at the corners of

buildings.

The field affected is relatively local and exists between the side of

the building or tower (where pressure is low) and a maximum space equal to

the width (or thickness) of these structures.

For parallelepiped structures around 15 m high (5 stories) the comfort

parameter is 1.2 and for heights greater than 35 m this level is exceeded

without going higher than 1.5. In the case of a compact group of structures,

the screening relative to the dimensions of the wind is greater, and the

discomfort level is generally higher than in the preceding case. A way of decreasing the corner effect is to extend the buildings by

adjacent structures of decreasing height (up to 1 storv^

29
Raised horizontal

gradient

and thus to permit the wind to clear the "corner" largely at some distance

above the surface.

In the case of a tower between 35 and 45 m high, the parameter \\) stops at 1.4, but for very high towers (100 m average), 4> reaches 2.2.

In this case there is a critical spacing of some 2 times the transverse

dimension of the towers, for which the discomfort level (average about 2)

is extended over the whole space between the two towers. While for

spacings higher or lower than the critical the discomfort level decreases,

the very tall groups are especially subject to discomfort and require

particular attention by designers.

NOTE: This effect develops from very high horizontal velocity gradients.

Wake Effect

The wake of an object is created by fluid circulation behind the

object between the separation lines from the edges.

Discomfort in the wake results not only from excessive speeds where

zones of different pressure join but also from a strong turbulence effect

caused by eddy circulation that is more or less stable and persists

30
for a long time in the lee of the object. It is quite evident that the manner

in which a wake can "spread out" is a direct function of the immediate

environment upstream and downstream)

.

By definition the wake effect includes the corner effect which causes

the highest discomfort levels in wakes.

Speaking generally, the comfort parameter in the structural environment

varies in wakes between the following values: —For tall buildings, 1.4 to 2.2, depending on the height (16 to 30

stories), without going below unity in the affected zone, and laterally

of the same order as the thickness of the building, downstream for a distance approximately equal to the height. —For parallelepiped buildings of 16 stories, from 1.6 to 0.5 if the

overall dimensions of the object are sufficient (3 times the height).

The affected zone is laterally of the order of twice the thickness

of the building and downstream from 1 to 2 times the height.

31
Channeling Effect

A structural group forming a corridor or channel open to the sky is

not a cause of discomfort per se but, when associated with an anomaly,

may transmit it for its whole length. The corridor phenomenon functions

much better when it is well defined (not very porous, etc.) and is

relatively narrow (less than 3 times the average height of the buildings

that form it). We can decrease this effect by introducing deflectors or changes in direction.

Pyramid Effect

This method of construction, by its rather aerodynamic geometry, does

not offer massive resistance to the wind and, because of its surface

roughness (stepped effect of stories and balconies), appears to dissipate

maximum wind energy in all directions.

At the ground, the average comfort level is around 0.6 (with a large

turbulence component) in a spatial plan of this type.

The critical zones are at the "composite windward corners" of the

pyramidal structures, and for 13 stories the parameter \\) reaches 1.6.

On balconies toward the wind, near the crests and starting at the ninth

32
story ip can go beyond unity and reach 1.6 for a 17-story structure. However,

it may be noted that for 80% of the balconies the comfort parameter is

around 0.5.

It is quite evident that if attention is given to the two types of

exposed zones mentioned above, with even a little care this method of

construction is especially to be recommended.

Wise Effect

A. F. E. Wise was the first to describe this effect [13]. For structures

higher than 5 stories the incidence gradient causes a distribution of over- pressures that differ with height on the windward face. At the base of the

building a turbulent zone forms where \\) can reach 1.5 for a building some

60 m high, and even 1.8 if upstream (with incidence at right angles) a low

structure (e.g. 5 stories) is located at a distance approximately equal to

the height of the low structure. The arrangement of the two buildings is

thus said to be "critical."

NOTE: This zone of turbulence is particularly troublesome where the local

direction of flow can be vertical.

33
Chronophotographic visualization of Wise effect

Turbulent

vertical

component

Turbulent zone

at the base of

a building

34
Figure 12

c

•H

0.2 0,4 0,6 0.8

ijj, true value

1,2

Fig. 12. Comparison of values obtained

in wind tunnel and on the ground

.

8 . True Magnitude Study

The "old construction"

sample, taking into account its

installation (Nantes) and the

truth of the model, allowed us

to compare the results obtained

in the wind tunnel with measurements on the ground and thus to

confirm the quality of our test

averages (Fig. 12).

On the ground , for a given

wind direction (measured at the

CSTB station at Nantes) , the

average speed (for 10 min) and

the turbulence intensity were

recorded simultaneously on a 7-meter pylon at a remote site (reference location) and 2 meters above the ground using a portable tripod (some 10 points)

.

The anemometers being very sensitive (frequency response close to 1 Hz)

,

we could correctly measure the turbulence intensity and calculate the

parameter ty locally.

Comparison of the results with those obtained in a wind tunnel is con- sidered excellent. We only regret that the number of points for comparison

was too limited. (To compensate for this lack, a broader study is underway.)

9. Conclusion

This work allowed defining and quantifying in their structural context

the different "aerodynamic accidents" that may cause discomfort to pedestrians

due to effects of wind and thus how to prevent them in some cases,

It is quite evident that our quantification can be applied strictly

only to an open-country wind. However, an approximate correction that takes

the irregularities of the terrain into account is indicated.

Further, the comfort criterion adopted can be confirmed in the future;

it is sufficient to adjust the values on the basis of the new criterion.

35
This type of study indicates some arrangements favorable to comfort or

to decreasing the manifestations of the wind.

Finally, it was possible for us to translate this work into simple

rules or practical suggestions for the use of city planners and

designers [3].

The CSTB is now studying aerodynamic shapes, artificial and botanical

wind screens, and also deflection arrangements at the scale of the building.

These new studies will make it possible to provide architects with "afterthe-fact" or "remedial" measures and will finish off the work which we have

just described.

36
References

1. J. Gandemer, "Discomfort due to Wind at Approaches to Buildings:

Aerodynamic Study of Speed Field in Building Groups," ADYM 12-73.

2. J. Gandemer and G. Narnaud, "Discomfort due to Wind at Approaches

to Buildings: Aerodynamic Study of Speed Fields in Building Groups,

Complementary Study." ADYM 1-75

3. J. Gandemer and A. Guyot, "Methodological Guide and Practical Plans

for Including Phenomena Due to Wind in designing Urban Groupings,"

in preparation.

4. J. Gandemer, Cahiers du CSTB. note 141

5. C. Hautoy, "The CSTB Wind Tunnel with limited bed," ADYM 12-73.

6. C. Sacre, "Wind in the Planetary Limited Bed," CLI 10-73

[All the above references are in French]

7. N. H. Melbourne and P. N. Joubert, "Problems of Wind Flow at the

Base of Tall Buildings and Structures," Tokyo 1971. Conferences

on Wind Effects on Buildings and Structures.

8. T. V. Lawson, "The Wind Environment of Buildings: a Logical

Approach to the Establishment of Criteria," University of Bristol,

Aeronautical Department, Eng. TVL/7301, 1973.

9. A. D. Penwarden, "Acceptable Wind Speeds in Towns," Building

Science, Vol. 8, No. 2, Sept. 1973.

10. J. C. R. Hunt, E. C. Poulton, and J. C. Mumford, "The Effects of

Wind on People: New Criteria Based on Wind Tunnel Experiments,"

to be published in Building Science.

11. J. C. R. Hunt, "Wind Tunnel Experiments on the Effects of Wind

on People, BRE, Sept. 1974.

12. N. Isyumov and A. G. Davenport, "The Ground Level Wind Environment

in Built-up Areas," International Conference on Wind Effects on Buildings and Structures, London, Heathrow, Sept. 1975.

13. J. Gandemer, "Wind Environment around Buildings: Aerodynamic

Concepts," International Conference on Wind Effects on Buildings

and Structures, London, Heathrow, Sept. 1975.

14. J. Gandemer and G. Barnaud, "Simulation of Dynamic Properties of

Wind by Neutral Stability in the CSTB Wind Tunnel with Limited Bed"

[in French]

.

15. J. Gandemer and H. Maille, "Method of Quantitative Visualization

Applied to the Study of Air Flow in Groups of Buildings," to be

published [in French].

37
Appendix 1. Theoretical Expression of Conversion Coefficient

Zm

I 400

330

270

= k

Z c.c.

country site ^ (slight, irregularity)

- / 10 \

- 14 Uiometeo Uq I 270/

Zosub \330/

_ UG (Zo_\*

m

suburban

(moderate irreg

site k = (270p / M»-

ularitv) VJO; \330J -ty) \^J

1,59

/270\ ' 14 z

0,36 (great

city

irregularity)

center site * = ^- ^

1.59 Example

For z =

Country

Suburb

City center

10 metres : k= 1 £~0.66

£ = 0.42

[sub = suburb]

[c.c. = city center]

38
Appendix 2. Weigh t ing of Quantitative Results as a Funct ion of

Geographical Site and Irregularity

We explained in Sect. 4.33 the correspondence between the comfort

parameter \\) and the local frequency of exceeding the discomfort threshhold. This correspondence assumes knowledge of the specific statistical meteorological data of each site. Therefore it is essential for

the designer to use the climatic data of the place if he wants to associate the \p values for his site correctly with the frequencies of

corresponding discomfort.

At the same time, if an aerodynamic anomaly of the parameter \p obtained for a wind of the country type is located in a suburb or a city

( aerodynamically thus subjected to a wind of the suburb or city type)

the discomfort level and thus the associated discomfort frequency will

not be the same. We suggest below a method of weighting the value of the parameter

ty (obtained strictly for a wind of a = 0.16) according to the nature

of the irregularity met by the wind.

From the results obtained on a spatial plan (see note on p. 21)

subjected to three types of wind, we found that (on the collection

of points measured in the spatial plan) the parameter

U (1 +1)

U40 site

had the same average.

In attempting a better knowledge of the effect of the irregularities

upstream, it seemed reasonable to use the \\) values that were found by

measurement and the gradient a = 0.16 to calculate the frequency of

the discomfort for other gradients, assuming the parameter (j)^ to be

constant for any value of a. In our calculations we adopted the following thicknesses of the

limited bed for the different a values:

a ZGmeter

0.14 270

0.16 280

0.25 330

0.36 400

39
For example, with Z = 2 m and a = 0.16, we have

_ 17 \0.16 _ _

Ur = Iff] U,„ 0.72U„JM \IU/ .He 0.10

where Ui qm

is the average speed measured at the meteorological station

(a = 0.14).

Assuming in first approximation that the standard deviation is

independent of the irregularity and the height, we can write

(I i U

I. r r

- U 10M 10M with 10M - 0.18

Therefore

JJ (1 +1) _ U (1J-I)

* Ur (1 + U) 0.9 U 10m

or U (1 +l) = 0.9U10M +

The parameter (J) can be expressed

U (1 + I) 0.9 TT^- + U 10 site U 40 site

The relation between cj). and ij> for a = 0.16 will be

cj> A = 0.78 \\>

Assuming that cj). does not depend on a, the discomfort will start when

U(l + £) = 6 m/sec

or _ _6_

Uiom "~ 0.78

U, OM MO

X

+

MOM

The ratio U 4

is determined as a function of the irregularity (roughness) and we have

the following conditions for the start of discomfort:

_ 6.31 a =0,14 rase campagne U 10m — —

;j7~

6.62

a = 0,16 campagne

basse banlieue

a = 0.25 banlieue

k = 0,36 centre ville

UlOM ty - 8,23

UlOM _

ty 11 UlOM - ^

[open country]

[country, low suburb]

[suburb]

[center of city]

40
Thus, regardless of the region, the same discomfort frequency is reached in

open country with 0.954, in suburbs with 1.254, and in the city center with 1.74

with the "4" values given in the preceding paragraph (where the wind in the country is a - 0.16)

.

Further, if a quantified anomaly for a country wind (a = 0.16)

locally has a value \p - 1, this same anomaly in a suburb will be only

0.8 ty or in the city 0.6 ty. The values of \\j are always those measured

for wind of country type (a - 0.16).

Theoretically the above material assumes a wind "statistically" in

an established regime, i.e. an upstream distribution of irregularities

that is relatively homogeneous for several kilometers.

If now we consider the effect of a change in irregularity on the

comfort parameter, we can only give some general experimental conclusions:

When a country-type wind penetrates into a spatial plan, the zone

of probability of aerodynamic accidents is a band of the order of 200 m

thick. The discomfort levels there are those given in the study of

the different anomalies of aerodynamic effect.

Beyond this band, the probability of accidents is less and we can assume roughly that events occur as though we were in a wind of the

suburban type, or for a discomfort parameter of 0.8 ty. It should be mentioned, however, that this change or "mask effect"

can be less for widely different structures (h > 2h) above the average level

(thus maintaining the ty values without attenuation)

.

If open (or free) spaces with minimum area of the order of 400 x 400 m

are present, the wind "falls down" into such spaces and the peripheral

buildings are again exposed to a 200-m band in the direction of penetration

of the wind.

By way of comment, we can indicate that tall groupings consisting half

of towers do not ever produce the least mask effect (interference among

themselves) . Old structures, by their high density favor the protection effects

(average ip - 0.6 to 0.7) and the aerodynamic accident thresholds that can occur are at the base of very high structures (100 m) (installation to the rear of the spatial plan). The possible discomfort zone caused by this is

roughly a circular area whose radius is equal to the height of the structure. At the very base of tower structures (h - 100 m) the discomfort

parameter can reach 1.6.

41
NBS-114A (REV. .-1-77)

O.S. DEFT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS TN 710-92. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

BUILDING RESEARCH TRANSLATION:

Discomfort Due to Wind Near Buildings:

Aerodynamic Concepts

5. Publication Date March 1978

6. Performing Organization Code

7. AUTHOR(S)

J . Gandemer

8. Performing Organ. Report No. (S. G. Weber, Translation Editor)

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP) 13. Type of Report & Period Covered Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 2 00- word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) Flow patterns at ground level in groups of buildings result from the complex

interaction between the wind (impact, average speed distribution with height,

and turbulance) and the buildings themselves (shapes, sizes, arrangements, etc).

The increase in the number of very tall structures and the more or less arbitrary, with respect to wind, placing of large structures have frequently demonstrated the lack of adaptation of the structural environment to wind phe- nomena. Manifestation at ground level, such as zones of high speeds or eddies,

make the approach to buildings uncomfortable (sometimes even dangerous) for the

pedestrian.

Elimination of theses problems requires better knowledge of air flows around

structures and formulation of practical plans that the architect or city planner can use in designing larger structural units. This report summarizes work

carried out at the CSTB institute in Nantes in 1973 and 1974 and gives the main

results of the study.

A guide is included which furnishes simple rules or practical advice that can

be used by architects and city planners.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Air flow; CSTB; discomfort, wind; France; translations; wind discomfort; wind

flow around buildings.

18. AVAILABILITY [X1 Unlimited

]] For Official Distribution. Do Not Release to NTIS

|v ! Order From Sup. of Doc, U.S. Government Printing Office *~^ Washington, D.C. 20402, SD Stock No. SNOOJrOPJ

^] Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES.

48

•22. Price

$ 1.60

USCOMM-DC 66035-P7E
Waste Heal

Management

Guidebook

A typical plant can save about 20 percent of its fuel—just by installing waste heat recovery equipment. But with so much equipment on the market,

how do you decide what's right for you?

Find the answers to your problems in the Waste

Heat Management Guidebook, a new handbook

from the Commerce Department's National Bureau

of Standards and the Federal Energy Administration.

The Waste Heat Management Guidebook is designed to help you, the cost-conscious engineer or manager, learn how to capture and recycle heat

that is normally lost to the environment during in- dustrial and commercial processes.

The heart of the guidebook is 14 case studies of companies that have recently installed waste heat recovery systems and profited. One of these applications may be right for you, but even if it doesn't

fit exactly, you'll find helpful approaches to solving

many waste heat recovery problems.

In addition to case studies, the guidebook contains

information on:

• sources and uses of waste heat

• determining waste heat requirements

• economics of waste heat recovery • commercial options in waste heat recovery equipment

• instrumentation • engineering data for waste heat recovery • assistance for designing and installing waste

heat systems

To order your copy of the Waste Heat Management

Guidebook, send $2.75 per copy (check or money

order) to Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

A discount of 25 percent is given on orders of 100

copies or more mailed to one address.

The Waste Heat Management Guidebook is part of the EPIC industrial energy management program

aimed at helping industry and commerce adjust to the increased cost and shortage of energy.

U.S. DEPARTMENT OF COMMERCE/ National Bureau of Standards

FEDERAL ENERGY ADMINISTRATION/Energy Conservation and Environment
There's

anew

look

W^-X? 1 / ... the monthly / >^^ ^^V^ / / magazine of the Nation-

^V. ^^^^^^^/ a ' Bureau of Standards.

^ ^^^^ / Still featured are special ar- %^^^Ty tides of general interest on \ y / current topics such as consum- \n^ ^x er product safety and building

technology. In addition, new sections are designed to . . . PROVIDE

SCIENTISTS with illustrated discussions

of recent technical developments and

work in progress . . . INFORM INDUSTRIAL

MANAGERS of technology transfer activities in Federal and private labs. . . DESCRIBE TO MANUFACTURERS advances in the field of voluntary and

mandatory standards. The new DIMENSIONS/NBS also

carries complete listings of upcoming conferences to be

held at NBS and reports on all the latest NBS publications,

with information on how to order. Finally, each issue carries

a page of News Briefs, aimed at keeping scientist and consumalike up to date on major developments at the Nation's physical sciences and measurement laboratory.

(please detach here) SUBSCRIPTION ORDER FORM

Enter my Subscription To DIMENSIONS/NBS at $12.50. Add $3.15 for foreign mailing. No additional postage is required for mailing within the United States or its possessions. Domestic remittances should be made either by postal money order, express money order, or check. Foreign remittances should be made either by international money order, draft on an American bank, or by UNESCO

coupons.

Send Subscription to:

Remittance Enclosed (Make checks payable

to Superintendent of Documents)

D Charge to my Deposit Account No.

NAME-FIRST, LAST

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 II 1 1 1 COMPANY NAME OR ADDITIONAL ADDRESS LINE

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 II 1 1 1 1 1 1

STREET ADDRESS

1 1 1 1 1 1 1 1 1 1 1 1 II 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

I I I I I I I I I I I I I I I I

MAIL ORDER FORM TO:

Superintendent of Documents Government Printing Office Washington, D.C. 20402

PLEASE PRINT

* U.S. GOVERNMENT PRINTING OFFICE: 1978—261-238/30
NBS TECHNICAL PUBLICATIONS

PERIODICALS

JOURNAL OF RESEARCH—The Journal of Research

of the National Bureau of Standards reports NBS research and development in those disciplines of the physical and

engineering sciences in which the Bureau is active. These

include physics, chemistry, engineering, mathematics, and

computer sciences. Papers cover a broad range of subjects, with major emphasis on measurement methodology, and

the basic technology underlying standardization. Also in- cluded from time to time are survey articles on topics closely

related to the Bureau's technical and scientific programs. As

a special service to subscribers each issue contains complete

citations to all recent NBS publications in NBS and non- NBS media. Issued six times a year. Annual subscription: domestic $17.00; foreign $21.25. Single copy, $3.00 domestic;

$3.75 foreign. Note: The Journal was formerly published in two sections: Section A "Physics and Chemistry" and Section B "Mathematical Sciences." DIMENSIONS/NBS

This monthly magazine is published to inform scientists, engineers, businessmen, industry, teachers, students, and

consumers of the latest advances in science and technology,

with primary emphasis on the work at NBS. The magazine

highlights and reviews such issues as energy research, fire protection, building technology, metric conversion, pollution

abatement, health and safety, and consumer product per- formance. In addition, it reports the results of Bureau pro- grams in measurement standards and techniques, properties

of matter and materials, engineering standards and services, instrumentation, and automatic data processing.

Annual subscription: Domestic, $12.50; Foreign $15.65.

NONPERIODICALS

Monographs—Major contributions to the technical liter- ature on various subjects related to the Bureau's scientific and technical activities. Handbooks—Recommended codes of engineering and industrial practice (including safety codes) developed in cooperation with interested industries, professional organizations, and regulatory bodies.

Special Publications—Include proceedings of conferences sponsored by NBS, NBS annual reports, and other special

publications appropriate to this grouping such as wall charts, pocket cards, and bibliographies.

Applied Mathematics Series—Mathematical tables, manuals, and studies of special interest to physicists, engineers,

chemists, biologists, mathematicians, computer programmers,

and others engaged in scientific and technical work.

National Standard Reference Data Series—Provides quantitative data on the physical and chemical properties of

materials, compiled from the world's literature and critically evaluated. Developed under a world-wide program co- ordinated by NBS. Program under authority of National

Standard Data Act (Public Law 90-396).

NOTE: At present the principal publication outlet for these data is the Journal of Physical and Chemical Reference Data (JPCRD) published quarterly for NBS by the American Chemical Society (ACS) and the American Institute of Physics (AIP). Subscriptions, reprints, and supplements

available from ACS, 1155 Sixteenth St. N.W., Wash., D.C.

20056.

Building Science Series—Disseminates technical information developed at the Bureau on building materials, components,

systems, and whole structures. The series presents research

results, test methods, and performance criteria related to the

structural and environmental functions and the durability and safety characteristics of building elements and systems. Technical Notes—Studies or reports which are complete in themselves but restrictive in their treatment of a subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subject area. Often

serve as a vehicle for final reports of work performed at NBS under the sponsorship of other government agencies.

Voluntary Product Standards—Developed under procedures

published by the Department of Commerce in Part 10, Title 15, of the Code of Federal Regulations. The purpose

of the standards is to establish nationally recognized require- ments for products, and to provide all concerned interests with a basis for common understanding of the characteristics of the products. NBS administers this program as a supple- ment to the activities of the private sector standardizing

organizations.

Consumer Information Series—Practical information, based on NBS research and experience, covering areas of interest to the consumer. Easily understandable language and

illustrations provide useful background knowledge for shopping in today's technological marketplace.

Order above NBS publications from: Superintendent of Documents, Government Printing Office, Washington, D.C.

20402. Order following NBS publications—NBSIR's and F1PS from

the National Technical Information Services, Springfield, Va. 22161.

Federal Information Processing Standards Publications (FIPS PUB)—Publications in this series collectively constitute the Federal Information Processing Standards Register.

Register serves as the official source of information in the Federal Government regarding standards issued by NBS

pursuant to the Federal Property and Administrative Services Act of 1949 as amended, Public Law 89-306 (79 Stat. 1127), and as implemented by Executive Order 11717

(38 FR 12315, dated May 11, 1973) and Part 6 of Title 15 CFR (Code of Federal Regulations).

NBS Interagency Reports (NBS1R)—A special series of

interim or final reports on work performed by NBS for outside sponsors (both government and non-government).

In general, initial distribution is handled by the sponsor;

public distribution is by the National Technical Information

Services (Springfield, Va. 22161) in paper copy or microfiche form.

BIBLIOGRAPHIC SUBSCRIPTION SERVICES

The following current-awareness and literature-survey bibli- ographies are issued periodically by the Bureau:

Cryogenic Data Center Current Awareness Service. A litera- ture survey issued biweekly. Annual subscription: Domestic, $25.00; Foreign, $30.00.

Liquified Natural Gas. A literature survey issued quarterly.

Annual subscription: $20.00.

Superconducting Devices and Materials. A literature suTvey

issued quarterly. Annual subscription: $30.00. Send subscription orders and remittances for the preceding bibliographic

services to National Bureau of Standards, Cryogenic Data

Center (275.02) Boulder, Colorado 80302.
U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Washington. DC. 20234

OFFICIAL BUSINESS

Penalty for Private Use. $300

POSTAGE AND FEES PAID

U.S. DEPARTMENT OF COMMERCE COM-21S

SPECIAL FOURTH-CLASS RATE BOOK