The penetration of rain through an annular air-curtain dome

f

ugust,

1971.

-.,

.

(

THE PENETRATION OF RAIN

TECHNISCHE

HOGESCHOOL

OELFl

VUEGTUIGOOUWI(UNOF

BISUO"fHEfK

THROUGH AN ANNULAR AIR-CURTAIN DOME

by

R. Lake and B. Etkin

THE PENETRATION OF RAIN

THROUGH AN ANNULAR AIR-CURTAIN DOME

by R. Lake

and

B. Etkin

Submitted February, 1971.

SUMMARY

Investigations have been carried out on a 12 in. diameter model as to the energetic feasibility of protecting a region of space from rainfall by means of an annular jet enclosure. The results of the experiments indicate power

requirements, in the absence of side wind, of .05-0.1 HoP./sq. ft. 'dry' area.

Although this is very encouraging many problems exist~which will require

consi-derable research effort. Scale effect, the performance in a side wind, the

problem of heating the interior, and the turbulence structure of the interior

are among those which need study. A theoretical analysis indicates that the

power per unit area approaches a constant for 'large' diameters, but a

1. lI. lIL Summary Not a;bi on INTRODUCTION EXPERIMENT 2.1 The Facility

(a) The Annular J,et (b) The Rain Shower

TABLE OF CONTENTS

2.2 Photographs of the Rain Shower

2.3

Jet Velocity Calibration

2.4

Measurements

(a) Water Collection Functions (b) The Effect of Swirl

DISCUSSION

3.1

3.2

3.3

3.4

Problems Encountered in the Experiment

Sealing and Penetration Criteria

Conservative and Unconservative Factors Experiment Future Work REFERENCES FIGURES 1 to 10 in the -.I. PAGE 1 2 2

3

4

4

5

5

5

8

9

10

NOTATION

H dome height d drop diameter t jet thickness D jet diBlIDeter Ü - V.

J mean jet velocity V

t drop terminal velocity

p air density Pw water density 9 collision angl.e c 9 0 j et exit angle g gravitational acceleration 6.W , 6.W

r 0 water collected at velocity

V.

J

I. INTRODUCTION

In a recent paper(l) the possibility of protecting a portion of space by means of an annular air jet was discussed. Such a jet tends to form a dome-like enclosure above the annulus and thus gives rise to the notion of an 'air dome' (see Fig. 2). It was the aim of this investigation to obtain certain basic information about these jets with respect to the problem of protecting the in-terior space from rainfall.

Basically the flow field of the jet is determined by three parameters, the jet exit velocity, the jet thickness and the diameter of the enclosed area. If we consider protection from rainfall we must also add as parameters the

terminal velocities and diameters of the drops. The experiments described herein provide some initial information on what combinations of these parameters will result in protection of the area within the annu~us.

0ne of the difftculties in speculating about this device is the 2ack of fundamental information concerning the annular jet and its interaction with particulate showers such as rain or snow. I~ is essential that a quantitative understanding be had of these interactions prior to undertaking any design or

development work regardless of the engineering or architectural application envisioned.

T~e present work has attempted to deal with the feasibility in terms of energy of the device when no side wind is present. All the numerical results cited in this report would be quite different if a side wind were present. Visual observation of the effect of tilting the jet (in. effect simulating a slight side wind) indicates that this effect may be large. Certainly particles possessing a velocity component perpendicular to the jet axis have a better chance of pene-trating the jet than those which do not. What effect the wind will have on the jet flow field is not known. Essentially a repetition of the present work is required with additional facilities for the introduction of a side wind.

If the air dome proves feasible in reasonable side winds then the nature of the flow field within the dome should be investigated. At present (from tuft observations) we have a good qualitative understanding of the general flow pattern inside the jet (see Fig.

3).

Recent work reported in Refs. 2,

3

and

4

provides a more quantitative picture. In addition to knowing the mean velocity field and its dependence on the jet velocity we must also know the structure of the turbu-lence within the dome. The scale and intensity of the ~urbulence inside the dome will influence the suitability of the annular enclosure for architectural applications. Again this is a problem for experimental investigation.

Another problem related to the nature of the flow field concerns its transport properties, i.e., the heat and mass transfer out of the 'enclosed'

region. The feasibility of maintaining a positive or negative temperature differen-tial with respect to the ex~erior depends on the magnitude of the heat transfer

from the cavity. The heat tr1ansfer will be closely related to the mass transfer

from the cavity which may be itself of interest in some applications of annular

air curtains. During these experiments, difficulties were encountered with evapo-ration of water from the collecting pans. Although no good details are available, estimates from data indicate that evaporation rate can be as high as 1/2 tb 1% of the rainfa11 rate.

dimensions, the fundamental dimension here being the 'dome height', the vertic~l

distance to the jet 'collision ' region . The theoretical analysis of Chaplin~.,5 J.;ds of some interest irt this connection. From a rather simple momentum analysis he

derives the following relai{ion for dome height (see Fig.

3),

·

where H

D

H dome height

=

sin8 - sine c 0 2( coss -cose ) c 0

D diameter of pr6tected area

8 is determined from the jet entrainment function

c.

1 cose c = f

(~t :~:8

8

~coS8

)

c 0

The essential point here is that dome height depends upon the ratio jet thickness/

jet diameter.

The limiting case of an infinitely thin jet (D/t ~oo) provides the

following relation H D = 1 + sin8 o 2cose o

All of the jets considered herei~ have e

=

0 so that H/D

=

1/2.

agreement with tuft observations made d~ing these exp~~~ments.

data on 'dome height' is also available for thick jets\ J.

This is in good

Same further

In addition to knowing the 'limiting' physical dimensions of the dome

we may wish to know effective, application-oriented dimensions. For example,

the magnitude of the internal velocities may be such that the habitable space

is but a fraction of the physical dome dimensions, An understanding of the

in~ernal flow field should permit the definition alld determination of such

'application' dimensions.

Apart from prob~ems concerned only with the air jet there is a whole

range of probtems involving the interaction of particles and the jet stream.

Significant phenomena such as drop coalescence, drop breakup and drop refraction (in viscous shear flow) have r~ge~ved some investigation-, but a full understandi~g

has not as yet been aChieved(6)\7J..

It is the clear quantitati~e understanding of the above phenomena that must precede engineering design. The present experiments stand as an initial step

that indicates the device may be feasible. tConsiderable additional research will now be required in order that the potentialities of this device may be realized.

11, THE EXPERIMENT

2.1 The Facility

(a) The Annular Jet

The central device in this facility consists of a vertically oriented

axisymmetric flow at the jet exit (Fig. 1). To this end, three screens are placed upstream of the jet exit. The center portion of the annulus consists of a re-movable tapered cone. Four such cones are available providing jet thickness/jet diameter ratios of .017, .026, .036, .046. Each of these is fitted with a shallow metaJ., pan (1.5" deep) used to collect water which penetrates the jet. The pans are lined with steel wool to reduce splashing from the pan. Velocity measure-ments were obtained by reading a calibrated duct static pressure (see Sec. 2.3)

with a Betz manometer.

Measurement of water collection rates within the annulus was achieved by weighing the pans before and af ter a shower run.

(b) The Rain Shower (see Fig.i)

Approximately 10' above the jet exit was mounted a common household

shower head. Three different shower heads were tested although only one was used in the experiments. Water was supplied to the shower head via a plastic hose. Remote control of the shower was provided by a solenoid valve placed up-stream.of the shower exit. No control of the water line pressure was employed. Photographic studies of the raindrop velocities indicated that water pressure variations had little effect. The line pressure, and static pressure during a run, we re however monitored.

2.2 Photographs of the Rain Shower

In order to obtain results comparable with reality it is necessary to

simulate the rainfall as closely as possible. Ideally, one would like to have the resul ts herein as a function of raindrop diameter distributions. Restric·tions on time permitted only one type of rainfall to be tested.

Physically the rain c~n be described by two functions; the distribution functions of diameter and velocity. If the shower is comparable to rain, all of the drops should be at t,erminal velocity. Hence the velocity distribution

should be transformable via data on terminal velocities into the diameter dis-tribution, so that a single function suffices.

Determination of the velocity distribution was achieved by making photographs of the shower(exposure time :1/250 sec.) and measuring the length of

streaks produced by the raindrops. This was carried out for two different water line pressures (12 psi and 60 psi) for each of the three sho,wer nozzles. The velocity distribution function of the nozzle used in these experiments and the velmcity distribution for heayY rain (determined from P. F. Catton

1966)(9)

appear in Fig.

4.

The rainfall simulated in these experiments is exceptionally heavy; (rainfall rate

=

1000 mm/hr.). This is a very conservative factor in these experiments and should be born in mind wh en considering the statedper-formance data.

It was not possible to obtain good diameter photographs of the drops so that no direct diameter distribution data is available. Computer solution of drop velocities using empirical drag coefficients(8) indicated that all but the largest drops (

>

3

mm) reached terminal velocity (within

lo%)

in the

available distance. -It was thus assumed that the velocity distribution function obtained provided an adequate characterization of the rainfall.

2.3 Jet Velocity Calibration

Since it was not practical to place a velocity probe in the jet exit

with the shower on, a standard method of 'speed setting'(lO) was employed. The

method used is as fol~ows:

1. A velocity traverse was taken (.05" steps) at each of four stations spaced

90

0 _{apart on the circumference of the jet. The average of the four}

spatial-mean velocities for these stations was designated Ü. These velocity pro-files were determined at a single speed setting for all drums. The value ~f ij corresponding to a reference mass flow from the blower is denoted

U _re f '

2.

A

second reference speed denoted

U

is defined as the average of the four velocities measured at the mid-points of the four traverses.

U

Ü

was assumed independent of jet velocity.

3. Values of U (obtained from jet dynamic pressure ), Ps (at a point upstream

of the duct system) were measured and U plotted against Ps. ~Fi. '. ~) .

4. For ~ particular Ps ( that at which the velocity profiles were determined)

a

=

U f/U was _re computed. The U vs. P curve was then multiplied by _s

a

to yield the spatial mean velocity

Ü

vs. P. The procedure 1-4 was

re-peated for each of the four drum inserts.

SA

typical velocity profile

and a velocity calibration curve are shown in Fig. 5.

2.4 Measurements

(a) Water Collection Functions

The specific aim of this experiment was to obt.ain a series of functions relating water collection in the interior of the annulus to jet velocity, one for each of the jet thickness/diameter ratios. From such c~ves one can define

the 'dryness' of the interior arbitrarily, yielding a critical velocity of

.opera-tion. The set of all such V Ot' t/D pairs determines a V Ot vs. t/D function

crl crl '

from which the power per sq. foot of 'dry' area can be computed.

Measurement of the water collection rate was accomplished by running the shower for a fixed exposure time and weighing the accumulated water in the

collection pan. The length of the exposure time was 4 minutes except at lower

velocities in which 2-minute exposures were used. To limit variability due to

evaporation the jet was turned on 30 seconds prior to the shower and was shut i,

off 30 seconds af ter the shower. In addition each pan was dried to approximately a fixed weight prior to each run.

The results of the experiment appear in Figs. 6,7. It is evident that

at jet velocities of 60-70 ft./sec. less than 2% of the water penetrates the jet. Since we are concerned with a criticäl upper velocity the upper error bound should be used in defining a criticäl velocity.

Figure

8

shows the variation with t/D of the V .t inferred from the crl

scatter on these two plots results directly from the difficulty of assigning

precise values to V .t on the curves of Figs.6, 7, and we do not attach much

crl

significance to the shapes of the dashed lines drawn on them.

(b) The Effect of Swirl

Visual observation of the shower-jet system indicated that for some

velocities, drops that struck the curved (side) portion of the jet (Fig. 2)

were able to penetrate. It was thought that these drops might be kept outside

of the protected area if they possessed a tangential velocity component. To

investigate this swirl vanes were fitted to one of the drums (11.2" diameter).

The vanes were spaced approximately 1.2" apart around the circumference and were

set at angles of 150• The water collection function was then determined as

described above and the results are shown in Fig. 10. It is apparent that swirl

is not beneficial at least for the particular parameters of this experiment. The

reduction in the vertical velocity component produces a large change in the

velocity in the solid 'core' region of the jet. Since it is this region that

is most significant in preventing penetration, the water collection rate increased

when swirl was added.

lIl. DISCUSSION

3.1 Problems Encountered in the Experiment

During the experiment it was noticed that tilting of the drums produced

a large increase in the water collection rate. Very small deviations from colli-nearity of shower and jet axes produced sizeable increases in the penetration.

These points appear in Figs.

6, 7

as misalignment points. This appears to be due

to the fact that a ~arger proportion of the shower stream was now striking the

curved 'side' of the jet where penetration is easiest. The jet-shower axes

should be collinear within 20

3

0 in order to minimize this effect.

Another problem encountered was that of evaporation. Since this may

remove water which has penetrated the jet ( and give erroneous results for weight

of water collected ) it shou[d be controlled. For proper simulation the evapora-'

tion should not be eliminated as it will occur as well in a full scale device.

Th~ means that the ratio of evaporation rate to rainfall rate must be maintained

constant for both model and full scale. This would clearly be a difficult task.

One complicating factor at least in this experiment was the area increase

pro-duced by using steel wool pads to prevent splashing. Since just about any method

employed to reduce splashing will produce such an area increase relative to the

'collection area' the scaling of evaporati0nl®ay not be possible.

3.2 Scaling and Penetration Criteria

A crucial question that must be answered in assessing the energetic

feasibility of annular jets as shields against the environment is 'what is the

effect of the size of the system, i.e., of annulus diameter D?'. As a first

step consider a formal dimensional analysis. Let an annular jet characterized

by [V., t, DJ be exposed to a side wind of speed [WJ and a particulate

wind-borneJshower of geometrically similar particles characterized by [d, p' J . The

pertinent physical variables and constants of the system are then the preceding

ones plus [p, ~J the density and viscosity of both the wind and the jet, and

There is

6.

are

9

in all, V., t, D, W, ft, pI, P, iJ., g J so that the One fairly obvious choice

number of class parameters (dimensionless ratios)

for these is the following 7T l

=

pip' 7T 2

=

v./w

_J 7T

3

t/D 7T4 d/D 7T

5

=

V.tp/iJ. J 7T

6

=

v.

J 2/Dg

Thus dynamical similarity, requiring all these to be the same for large and smal~

systems, would from 7T

6

yield

V 2 a;CD

j

Dynamically similar systems would of course have the same relative rates of particle penetration into the centre. The above result for V. would lead to

enormous power requirements for full-scale annular domes. Th~ fact is, however,

that dynamical similarity would also require the raindrop diameter to be pro-portional to D (vide 7T

4

)

and the wind speed to increase with V., i.e., as

~ . J

~D (vide 7T

2). Thus exact dynamical similarity simply cannot exist for systems of

different size exposed to the same wind and rain, and the formal dimensional analysis cannot be expected to-prQvide useful information about scale.

A more fruitful approach is to consider the equations of motion of a particle in an arbitrary flow field, subjected only to drag and gravitational

forces. In so doing we ignore any effects that might(r~sult from the presence

of lift forces associated with jet velocity gradients

7).

To include these

would require that we know the law relating lift to flow shear, and this is not

available for the range of Reynolds number of interest here. For the important

case of strong sidewind, we speculate that the following theory is a gooli approximation.

Let the particle have mass m, let [u', v', w' ] be the fluid velocity,

[u, v, w ] the particle velocity, and g point in the negative z direction. Then we get, in a fairly straightforward manner

.

k (u-u')v u

-

-

_m k (v-v' )v v

-

-

_m

.

k (w-w' )v-g ( 1) w -

-m

.

-=

*

=

u, y = v, z

=

w 2 2 2 _{( , )2.} where v (u-u I) + (v-v' ) + w-w

---

-and k

These equations are made non-dimensional by dividing all

'11

= u/V., all distances by D, e. g., ~ = x/D-, and time by

" _t

₌

_{t/t*. Then the result is} J

d~ TIl (~

-

al) 1\

-

-

-

v dt d~ TIl (" 1\ I) ~

A -

-

v - v dt

d~

TIl

(0

A I) 1\

-

-

-

- w v - TI d1 22 d1/d't

=

1\ u, dy dt " / 1\

=

"

v,

d~/d~

=

w A where 2 TIl

=

kD/m, TI₂

=

Dg/V_j

Let us now examine TIl in more detail:

speeds by V., e.g., t* = D/V., Jso that

J

(2)

We see that TIl contains two of the nondimension~l parameters previously given

(TrI and Tr

4

),

and implicitly contains Tr

5

since CD is a function of Reynolds dumb er •

A

further very instruct~ve observatiort can be made about TIl asfollows.The

particle drag is

k~,

and when falling in still air at terminal velocit; V

t' mg=kV 2 t 2 or k -= mg/V t (

4 )

.

Thus TI

=

l.. kD m

=

~

2 mVt, Dg V 2 t

.

Thus TIl and TI

2 both have the form of Froude's numbers, and the third equation

of (2) may conveniently be rewritten

}

(6)

The question of scale effect may now be posed as follà>ws. Given systems in

which W, V

t ' Vj ' t/D are constants, how do the solutions depend on D? The

constancy of W/V. and t/D ensures that

[ÜI,

~I, ~I

]

are (apart from small

J

Let us consider the case TIl ~oo. On dividing (2), (6) by TI

_{i ,}

and

pro-cee~ing to the limit we get the result that the right-hand sides are zero, i.e.,

that

=

0

(a)

(b) (c)

The first two of these tell us that the projection on the horizontal plane of the

partiele paths coincides with that of the fluid streamlines. That is, as viewed

from above, the partieles are 'captured' by the f~uid •

. / 2 2 2'

Now v = V(u-u') + (v-v') + (w-w')

which _{from (7), (a,b) reduces to,after dividing by Vj '}

11

1"

/I, V

=

W - W (8) so that (7c) yields w-w C"A,~ I

~~O'

I -(V t/Vj )2 or (w-w' ) Iw-w' I _ V 2 t or w-w'

= -

V t

(9)

which is to say that thé partieles fall vertically relative to the fluid at rate

V

t whilst being convected horizontally.

We may infer directly ;from (7.) that the Bolutions, Le., the partiele

trajectories, are independent of system size (for constant Vt/V

J.

That is,

they are fixed curves in the [~,

y,

~J space. This being so, w~ can conclude

that the jet energy per unit area of enclosed circle is

P

=

~

P V} Aj

₌

const.

A

The power required per square foot of central area is thus seen to approach an

aSymptote as the diameter D increases. The parameter TIl' upon whose 'largeness'

this asymptotic approach depends, is roughly TIl

=

.1 D (for ~t = 18 fps), and

would equal 10 at D

=

100 ft. ThUB TIl

»

1 for D

>

100 ft. What the nature of

the function P(D) is, and at what values of D it approaches closely to its

asymptote only further research will reveal. .

3

.3

Conservative and Unconservative Fact~s~~ t~Ekperiment

In order to place the cited results in proper context we give here a

list of factors which although influential in the experiment could not be

re-moved.

(a) Evaporation - an unconservatiye factor believed to be'as large as l/~

to 1% of rainfall rate. '

(c) Rainfall Rate - this is undoubtedly an important factor. The extremely heayy rainfall simulated in these experiments (1000 mm/hr and high drop

velocity) make 4he results very cQ~servative.

3.4

Future Work

Many of the problems encountered in this experiment (and many of its

limitations) can be circumvented by the use of materials other than wate~ for

the drops in the simulation. Although there are problems with the simulatiön of large drops (such drops tend to flatten and break up) it provides the

possibility of moving to realistic d/D ratios at scales of 1/20th or 1/50th of

full scalè~ _ The side wind case can thus be treated without a very large tunnel

and its attendant cost. It is planned to build ~t UTIAS a f~cility in which

small glass beads will be used to simulate rain. This device possesses the added advantage that any type of rainfall, or for that matter-any form of pre-cipitation (snow, hail) can be simulated by varying the diameter distribution of the beads.

A quantitatiye knowledge of the detailed structure of the jet flow

field would permit the.calculatiQn of drop trajectories entirely from theory.

Experiments could then be conducted ·numerically on a computer. The large

number of parameters involved in physical experiments with these devices may make the computer technique very useful as an alternative.

1. Etkin, B. Goering, P. L. E. 2. Davies , T. Beer, J. 3. Chigier, N. A. Beer, J. 4. Patriek, M. Thring, M, 5. Chaplin, H. 6. Graham, W. 7. Saffman, P. G.

8.

GWln, R. Kinzer, G. D. 9. Catton,

;p. F.

10. Pope, A. ----_._._---_.~-- --REFERENCES

Air Curtain Walls and Roofs-Dynamic Structures. Proceedings of Conference on Architectural Aero-dynamies, Roy. Soc. of London, 1970.

The Turbulence Characteristics of Annular Wake Flow. Heat and Mass Transfer with Separated Flows. International Seminar +969 HERCIG -Nov. 1, Yugoslavia. _{, \}

The F the Nozzle in Double Concentric

Jets. 19

The Aerod namic Desi n of Pressure Jet Oil Burners. Combustion Aero Rept. Bo. CA Univ. of Exeter, Dept, of Chem.

Effects of Jet Mixing on the Annular Jet. DTMB AERO Report No.

L

915311

Feb, 1959.

Jet Stream Umbrella. B.A.Sc. Thesis, Engineering Science, University of Toronto, 1970.

The Li{t on a Small Sphere in a Slow Shear Flow.

Jour. Fluid Mech. VOl.22, pp.385-400.

Terminal Velocity of Fatl For Water Droplets in Stagnant Air. Jour. of Meteorology, Vol.

§,

No. 4, p.243. Aug, 1949. .

A Study of Raindrop-Size Distributions in the Free Atmosphere. Quarterly Jour. Royal Met. Soc.

Vol. 92, pp.15-30, 1966.

~ Preslure GauQe Solenoid L-Valve Valve DETAIL lAl Showerhead Drum Duet System

Pa

Tap

Rain From Water Supply collect-ing pan Drum Insert

t.

2S.J.₄ 1I

I

Drop Refractlon FIG. 2. . 0

t..

~tl

-SoIid 'Core' Portion Cavity Drop Penetrotion

FLOW REGIONS AND DROP PENETRATION

.2..

t..

Note:

80,

8_{c ore neQative os shown}

FIG. 3. QUALITATIVE DIAGRAM OF INTERNAL FLOW

(arter Chaplin, Ref. 5)

r

1.0 0.8 U) Q. 0 a: 0.6 Q 11. . 0 _0.4

z

0 ~ 0.2

~

a: 11. 0 4 I':- , •• • } AOAPTED FROM • RAl N - P.

F.

CATTON 1966

A}

_o

_{SHOWER -measured va}

.'

_,lues

0.1 mm/hr

8

12 16 . 20 ' 24 28 32 36

DROP VELOCITY

ft/lee

FIG.

4.

COMPARISON OF EXPERIMENTAL VELOCITY DISTRIBUTION WITH THAT OF NATURAL RAIN

90 80 70 u CD

..

:::: 60

....

z

-50

>-~ Ö

9

40

w

>

u

I

""

::

I;:)

~

(3

9

w

>

30 20 75 ~ 50 w

..,

0 2 50 3 VELOC/TY PROFILE 2.6% JET TH/CKNESS C/RCU MFERENTIAL STATION /

.

2 0

3

Il.

4 0

I. 4 5 6 7 8 9 /0 TRAVERSE STATION . ,

..

JET VELOC/TY CAL/BRAT/ON CURVE

2.6 % JET TH/CKNESS

JET THICKNESS

=

1.7 oIo JET DIAM ETER

JET THICKNESS

=

4.6

%

OF JET DIAMETER 1.0

₈

_{IN DICATES EFFECT OF} . , ' I "JET MISSALiGNMENT 0 0.8 ~

<l

... _0.6 > ~

<l

_0.4 0.2

•

0 0 30 40 50 60 70 80

SPATlAL MEAN JET VELOCITY

tt/.ee

1.0

JET THICKNESS

=

3.6

%

OF JET DIAMETER

~

0.8

<l

... 0.6 > ~

<l

_0.4 0.2 0 0 60 70

80

90

SPATlAL MEAN JET VELOC'TY ft/sec

~o <J ... ~ <J

z

o

t=

o

z

:::) aL

z

o

~

1&.1 ...J ...J

o

010% 1&.1

>

t=

j

1&.1 0:: JET THICKNESS - 3.6%

l%~---4~~~---~4~0~~--~50~--~~60~----~7~0----~---8~~---~o <l

'"

~ <l

z

0 ~ 0 Z j u.. Z 0 i= ~ ..J ..J

8

a:: kJ ~ ct ~ kJ

>

fi

..J kJ a::

JET THICKNESS - 4.6 % JET DIAMETER

I •

1%

V

_crit

=

eo

ft / •• c

®

INDICATE EFFECT OF JET MISSALlGNMENT

POINTS BELOW I % ARE PLOTTED ON 1% LI N E

I%--~--~--~~---~---~~---*----~~~

__

~

________

~

40 60 70 80 90

SPATlAL MEAN JET VELOCITY ft/ •• c

. FIG. 7(b) RELATlVE RATE OF WATER COLLECTION-LOG PLOT

u

~

...

....

20-r---r---,---r-~----~---~---0.1 ...: .08 1L.

o

f/) 06

, .

Q. :J: .0

o

.01

. 2

.O~

tlD

FIG. 8. VARIAl'ION OF V _cr~ ' t WITH t/D

o

.04 "..,..--

-

--/ "

'"

./

0

"'-.05

0 /

"-7'

o

"

o

~---r---~---~---~---~~-0.01 0.02 0.03 0.04 0.05

t./

0 . 6

1.0 _{RELATIVE RATE OF COLLECTION FUNCTION}

0

~ 0.8

/lW

v

I/lW

0 VS

;

JET VELDCITY

<J

"

JET THICkNESS

=

3.6 OIo of JET DIAMETER

; 0.6

<J

0.4

o jet with swirl

)( jet without swir'

0.2

0

_.

0 40 50 60 70 80 90

SPATlAL MEAN JET VELOCITY ft I sec

41

urIAS REPORT NO. 163

Institute for Aerospace Studies, U niversit:y of T oronto

The Penetration of Ra1n Tbrough e.n Annular Air-Curtain Dome

Lake, R. and Etkin, B.

1. Air Curte.1ns 2. Jets 1. Lake, R. e.nd Etkin, B.

10 pages 15 figures (approx)

3. Rain-jet Interaction II. tJrIAS REPORT No. 163

Investigations have been carried out on a 12 in. diameter model as to the energetic

feasibil1ty of protecting a region of space from rainfall by mee.ns of e.n e.nnular

jet enclosure. The results of the experiments indicate power requirements in the

absence of side wind, of .05-0.1 H.P./sq.ft. 'dry' area. Although this is very encouraging many problems exist whieh will require considerabie research effort. Scale effect, the performance in & side wind, the problem of heating the lnterior,

and the turbuleDce structure of the interior are among those whieh need study. A

theoretical analysis lndicates that the power per unit area approaches a constant for 'large' diameters, but a numerical value cannot yet be assigned to 'large'.

Available copies of this report are limited. Return this card to UTIAS, if you require a copy. urIAS REPORT NO. 163

Institute for Aerospace Studies, Universit:y of T oronto

The Penetration of Ra1n Through an Annular Air-Curtain Dome

Lake, R. e.nd Etkin, B. 10 pages 15 figures (approx)

1. Air·Curtains 2. Jets 3. Re.1n-jet Interaction I. Lake, R. e.nd Etkin, B. II. tJrIAS REPORT No. 163

Investigations have been carried out on a 12 in. diameter model as te the energetic

feasibility of protecting a regien af space from rainfall by means of an annular

jet enclosure. The results of the exper1ments indicate pawer requirements in the

absence of side wind, of .05-0.1 H.P./sq.ft. 'dry' area. Although this is· very

encauraging many problems exist which will require cansiderable research eftort. Scaie effect, the performance in a side wind, the problem af heating the interior,

and the turbulence structure of the interior are &mong those which need study. A

theoretical analysis indicates that the power per wlit area approaches a constant for 'large' diameters, but a numerical value cannot yet be assigned ta 'large'.

~

Available copies of this report: are limited. Return this card to UTIAS, if you require a copy.

urIAS REPORT NO. 163

Institute for Aerospace Studies, Universit:y of T oronto

The Penetre.tion of Ra1n Tbrough e.n A!mular Air-Curtain Dome Lake, R. and Etkin, B. 10 pages 15 figures (approx)

1. Air Curte.1ns 2. Jets 3. Rain-jet Interaction 1. Lake, R. and Etkin, B. II. tJrIAS REPORT No. 163

Investigations have been carried out on a 12 in. diameter model as to the energetic

feasibility of protecting a region of space from rainfall by means of an e.nnular

jet enclosure • The results of the experiments indicate power requirements in the

absence of side wind, of .05-0.1 H.P./sq.ft. 'dry' area. Although this is very

encouraging many problems exist which will require considerable research effort. Scale effect, the performance in a side wind, the problem of heating the interior,

and the turbUlence structure of the interior are ameng these which need study. A

theoretical analysis indicates that the power per unit area approaches a constant

for t large' diameters) but a numerical vaJ.ue cannet yet be assigned to 'large'.

Available copies of this report are limited. Return this card to UTIAS, if you require a copy. urIAS REPORT NO. 163

Institute for Aerospace Studies, Universit:y of T oronto

The Penetration of Rain Through an Annular Air-Curtain Dome

Lake, R. and Etkin, B.

1. Air Curtains 2. Jets

1. Lake, R. and Etkin, B.

10 pages 15 figures (approx)

3. Rain-jet Interaction

II. tJrIAS REPORT No. 163

Investigations have been carried out on a 12 in. diameter model as to the energetic feasibility of protecting a regian af space from rainfall by means of an annular

jet enclosure. The results of the experiments indicate power requirements in the

absence af side wind, of .05-0.1 H.P./sq.ft. 'dry' area. Although this is very encouraging many problems exist which wi11 require considerabie research effort. Scale effect, the performance in a side wind, the problem of heating the interior,

e.nd the turbulence structure of the interior are &mong those which need. study. A

theoreticel analysis indicates tbflt the power per unit area approaches a constant

tor 1 large ' diameters, but a numertcal value cannot yet be assigned to 'large 1 •