Effect of gas injection in separated supersonic flows

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MONITORING AGENCY DOCUMENT Nr. ASTIA DOCUMENT Nr

T.C.E.A. TN 7

EFFECT

OF

GAS INJECTION IN SEPARATED SUPERSONIC FLOWS

by

Jean J. Ginoux, Brussels University and TC

CONTRACT N° AF 61 (052) - 350 LAMINAR SEPARATION IN SUPERSONIC FLOO

FlNAL REPORT

February 1962

The research reported in this document has been sponsored by the Air Force Office of scientific research, through the European Office Aerospace Research, United States Air Forceo

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NOTATION

x distanee along the eentre-line of the model from the step-base y distanee perpendieular to the surfaee of the model

z spanwise axis

L length of the flat plate ahead of the step h step-height

S span of the model

':L non dimensional eoordinate = x/h

p statie pressure measured on the model surfaee

p

non dimensional statie pressure

p

= p/p~

Pb base pressure measured on the surfaee of the step

Ps statie pressure measured at x

=

42 mm and z

=

0, upstream of the pressure rise associated with the flow reattachment

f~ free-stream density

rct>

free-stream statie pressure M <Xl free- s tream Mach number

Ov(:p veloeity of sound in the free-stream \,A,O' free- stream veloei ty

S

boundary-layer thickness just before separation

e

momentum thiekness just before separation

Q

rate of injeetion in the separated region of the flow,

QB~' mass flow through the boundary-layer just before separation, C injeetion coeffieient defined by C

=

Q/

q q QBL

injeetion flow parameter defined by _~

_Q1

v~ = Ov

h.

?(1)

00 v veloeity of the air at the exit of the injection slot q dynamie pressure of the injeeted air

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1 SUMMARY

An experimental investigation has been made at a Mach number of 2021 on the effect of air injection in separated supersonic flows using two-dimensional backward facing step modelso This effect, in a laminar flow, was found to ~e ipdependent of the particular technique of injection when the rate of injection was smalle Air injection raises the base

pressure and decreases the pressure gradient at reattachment. At high rates of injection, considerable differences are found between the results obtained for various techniques of injection. It was also shown that the increase of the base-pressure is larger in the turbulent case than for a laminar boundary-layer. When freon gas was injected, it produced the opposite effect, namely of dec~easing the base-pressure at low rates of injection.

INTRODUCTION

The study of a laminar separated flow has a possible application as a means of reducing heat-rates in hypersonic flight. It is also

important as a basic phenomenon since the mechanism of flow reattachment is not very well understood. In particular, three-dimensional effects have been observed (ref.l) which in addition to a possible influence on heat-transfer and skin-friction, may shed some light on boundary-layer stability.

It is known that the flow over a considera~le distance downstream of the leadlng-edge of a hypersonic wing is supersonic. On the other hand, due to the high temperature invplved in slowing down the flow from

hypersonic to supersonic speeds, local Reynolds numbers are considerably lower than the stream-free Reynolds number. This result together with the fact that a favourable pressure gradient exists (nose effect) on the wing explains the existence of the very extensive laminar boundary-layers

that have been observ.ed (ref.2).

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2

severe _{aerodynamic heating, resulting from high stagnation}

temperature~" At present, _{two met:hods have been examined to solve this proble}ll. One method} makes use of mass-transfer _{cooling, such as injection through porous}

surfaces, _{use of ablation materials}_, _{e::c. as a means of heat relief.} Although a _{great amount of work has been done} _in_{this direction, many} aspects _{of this method remain to be solved.}

A _{different and very interesting approach to the problem of} aerodynamic _{heating consists in the possibility of subs}

tantially reducing the heat-transfer _{rates over major portions of the surface of the vehicle} by means of separated _{flows (ref. 2}

_{& 3). Chapman}

_{theoretically}_showed,

in the simpl_{e case of a th in boundary-layer,} _{that the}_{heat-transfer}

rates to the body are _{considerably reduced in regions of separated flows for}

both laminar and turbulent _{boundary-layers. He also showed} _{that gas injection} in the "dead-air" _{region of a separated laminar}_flow_has_a _powerful

effect in _{further reducing}_{the heat-transfer rate and}_even

that a modèrate amount of injection can reduce _{the heat flux to zero. Chapman's} _{conclusions were} verified by Larson (ref.4) for laminar flow in the Mach number range 3 to 4,

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but not for turbulent _{flow when the}_{measured heat-transfer}_{was very much} less than estimated. _{However, no test was made}_with_air_injection.

As a result _{of these investigations}

s it appears that laminar

separated flows _{at supersonic speeds may have a}_n _{appiication to the problem} of hypersonic flight. However, at present, theories covering separated flows at supersonic _{speeds provide a poor quantitative agreement with} experiment~ _{even in}_{the absence of heat-transfer} _(ref.5)

and, except for very simple _{models (zero boundary-layer}_thickness_{at sèparat}_i

on) the mechanism of flow _{reattachment and the effect of heat-transfer with or} without injection _{are only known qualitatively.} _In_{this respect,}

an experimental investigation _{was made to study the effect of gas injection} onsep_{arated supersonic flow. The study was to be made first in the absence} of _{heat-transfer» the}_{problem consisting in the development of a measuripg} technique which _{could provide reliable information.}_This

report is intended to present some _{of the results obtained.}

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3 DE5CR1PTION OF THE EQUIPMENT :

\-lj.nd tunnel

The investigation was made in the TeEA 40 x 40 cm2 (16°0 x 16°')

continuous supersonic wind-tunnel 5-1 at a Mach number of 2.21. A descrip-tion of the tunnel is given in reference 6.

Model configuration

The tests were made on backward facing step modele that completely spanned the working section of the tunnel. Two different

models were used which had the same step-he~ght (h

=

10 mm, abput 0~4 inch). They differed on1y by the length (L) of the flat plate ahead of the step, as shown in figure 1. Tbe rear part of the medels was initially designed by Nash (ref.7) in the farm of a hollow rectangular box in which

atmospheric air entered from the raar and exhausted near the step base through a rectangular slot that almost completely spanned the model.

By

testing the modelp Ban (ref.8) found that the rate of injection was not uniform along the span of the slot. He then improved the design by stretching cloth'"gauzes across tbe

flow

inside the model and by further èxpanding the air through a converging channel (with a contraction ratio of 2) leading to the exit-sloto This reduced the span of the slot to half tbe span of tha model (i.eo 20 cm). Retesting the mode19 Ban found a very good. uniformity of the injected flowp inasmuch as the velocity variations

+

were then leBs than - 2% of the mean velocity of injec.tion. The

modification was made by cutting the existing model into sections which were then reassembled af ter in,stalling the gauzes and the converging

channel. The model was then sealed with araldite.

An exploded view of the model is show~ in figure 3. SI and S2

are the cloth gauzes and C is the converging portion of the inside channel. The three parts AlBlD A2B2v and AlE3 of the model are fastened together

by a clamping plate (CP) and by the model-supports fixed to lts lower surface (not shown in the figure)o The shaded region (5) in the figure represents the slot-area obtained af ter assembling the model and P is the inlet pipe admitting atmospheric ai~ to the hollow model. Two longitudinal

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4

fences were used (F) to isolate the central portion of the separated flow, where the injection slot is located, from the two lateral regions not affected by injection. At th~ same time, these fences suppressed the cross-wind existing .. inside the separated re~ion of the flow, associated with the turbulent boundary-layers formed

én

the side walls of the test

section. Test set-up

The test set-up is schematically shown in figure 2. Dry airj supplied by the auxiliary dryer of tunnel 8-1, is driven through the injection system by the pressure drop from atmospheric condition at the inlet of the dryer to the loçal pressure in the tunnel (i.e. the base pressure which was approximately equal to 0.01 atm. absolute). The flow-rate was controlled by a throttling valve (V) and measured either by an • integrating flow meter or by orifice plates. These instruments were

calibrated to within 1% accuracy.

The supersonic wind tunnel was operated at stagnation pressures lower than atmospheric, because of power limitationso The stagna~ión 'pressure was

~intained constant at the desired

level by a regulating

valve (ref.6). The air leaking into the tunnel circuit by injection was removed by the pressure regulating system. It was therefore possible to maintain a constant stagnation pressure upstream of th~ supersonic nozzle to within 1% for the full range of injection flow rates (the maximum rate was about 180 litres per minute under standard atmospheric conditions).

All the measurements were made at a stagnation pressure of 150 mm Hg absolute and a stagnation temperature of about 293°K. Pressure measurements

The static pressure distribution was measured along;the centre-line of the models (upstream of the step, on th€ surface of the step and.on the surface upon which the supersonic flow reattached). Special care was taken to avoid an obstruction of the flow inside the model caused by the pressure tubes. These tubes were incorporated inside the cover-plate B3 (figures 1&2)

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running spanwise towards the model sides into grooves that were filled with araldite. The loeation of the statie pressure orifiees is indieated

in figure 1. The-pressures were measut;ed by a different:i:al pressure transducer and read on a strip chart recorder. Rotary valves, located inside the tunnel, were used to conneet all the pressure orifices to the same transdueer which was calibrated to within one percent accuraey.

Uniformity of injection

As stated above, t~e spanwise variations of the velocity of the injected air were less than

12%

of the mean iI!Jecti:gn-velocity. This is shown in figure 4 which gives the veloeity in metres per second at the slot as a function of the spanwise eoordinate (z) (z

=

0 being taken on

5

the centre-line of the model)~ _These results were obtained for a rate of about 90 litres per minute whieh is half the maximum rate that was used in the tests. The velocity was measured with a pit~ tube loeated at the

entrance of the slot when the tunnel was at rest and under vaeuum conditions. A similar measurement made with supersonic flow gave es.santially the same results.

SPAN EFFECT

In the course of a preliminary investigation made by Han (ref. 8) the statie pressure distribution was measured along the eentre-line of model 81-3 (without injection) and compared with the pressure distripution

recorded on an unslotted model without fences (model 8-3), whieh had the same step-height as model SI-3. The base pressure obtained on model 81-3 was 6% higher than that measut;ed on S-3 for the same stagnation pressure, and the maximum pressure gradient at reattachment was accordingly lower. This trend is similar to the effect of gas injeetion which is also to

inerease the base pressqre and deer.ease the pressute grad!ent. Han therefore concluded that this difference was eáused by the air leakage that existed at that time in the injection system resulting in a small amount of injection through the slot in the separated region of the flow.

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6

However, by later reducing this leakage by a factor of one hundred (i.e. down to an extremely small amount), the au thor reproduced

Hanls results which meant that the di~ference in base-pressures could not

be explained in terms of air-leakage. On the other hand, it was believed from pas.t experience that the presence of the slot and the inside cavity

of model 81-3 could not justify such a difference. It was then suspected

that the base pressure was influeneed by the presence of the flow fences which were used on model 81-3 to iso late the central slotted portion of

the model from the two unslotted side portions. Indeed, by removing these

fences the base pressure increased by 7%, while the maximum pressure gradient was reduced thus giving to within one perce~t accuracy the values measured on model 8-3. The comparison is made on figure· 5.

A further investigation of the phenomenon» reported in reference

9,showed that a cross-wind existed in the separated region of the flow~ caused by the turbulent boundary-layers on the side walls of the tunnel.

This cross-flow was suppressed by installing the fences and the corres-ponding base pressure was considered to be correct and representative of a two-dimensional flow.

EFFECT

OF GAS INJECTION ON LAMINAR BOUNDARY LA

YERS

:

It is practically~ossible to inject air without adding momentum

into the "dead-air" region of the flow. Indeed~ because of the limited

area covered by the separated flow, the velocity of the injected air is necessarily different from zero and increases with the rate of injection.

Consequently, the effect of air bleeding depends up on the direction and spanwise uniformity of the injected air. Moreover, a high velocity jet will

disturb the laminar boundary-layer and result in a displacement of the

transition region which will in turn modifythe. base pressure as well as the

pressure-gradient at reattachment. ( i.e. the initially laminar

reattachment might become transitional or even turbulent as ·a result of injection). In this respect, it was necessary to determine the maximum

rate of injection, below which the effects of air bleeding are independent of the particular technique of injection.

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7

The base-pressure ratio (i.e. the pressure measured on tne

centre-1ine of the step surface andreffe~dto the free-stream statie

pressure) is plotted i~ figure 6 against an injection coefficient (C

q),

using different tecbniques of air bleeding. In the present investigation,

the step-height was fixed and it was found convenient to refer the rate qf injection

(Q)

to the mass-flow in the boundary-layer

(QBL).

This

quantity has been computed, just befor~ separation, from the theory

of reference 10, assuming an adiabatie flat piate upstream of the stepe

It ean be shown that

where f

(l)

is the value of the Blasius function at tha edge of tha

boundary-1ayer (i.eo 3.68 for u

=

0.996 _{U oo} ); L is the length of tha

flat p1ate, Ss is the span of the injection slot, C is a coefficient

defined by

-1-and the subscript 00 is related to free-stream conditionso At a Mach

number of 2.21, a stagnation pressure of 150 mm Hg and a stagnation

temperature of 293

OK,

the value of QBL was eomputed as 0.22 kg/min

for the model 51-4 and as 0.305 for the model 51-30

Curve (a) of figure 6 is related to model SI~4~ where the air

was injected upwards through a 7 mm-wide slot. The model was fitted

with two rectangular fènces (11.5 mm high, 106 mm long and 0.5 mm thick)o

Curve (b) was obtained under the same conditions except: thaI: the width

of the slot was redueed" from 7 mm down to 2 tmn, in order to increase the velocity of the injection-jet for a given rate of bleedo Curve (c) is

related to down-stream injection. This was done by a slight modification

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8

Curve (d) compares the results obtained on model 81-3 for two different

sets of rectangular fences. The length of the fences was taken either as 106 mm or as 200 mmo Curve (e) shows the effect of spanwise variations of the velocity of injection. This was made by installing a comb, with flat wide teeth, above the 7 mm slot of model 8I-3, as shown in the sketch of figure 6.

For comparison, the pr·-essure ratio.

Ps

measured in the

separated region of the flow, 42 mm downstream of the step, is shown in figure 7 for the same test-conditions as for figure 6.

Figures6 and 7 show that the effect of air-bleeding was

identical in all test conditions, when Cq was lower than about 0.1

(*).

For higher values of the flow coefficient, the effect of air bleeding depended strongly upon the test conditions. The difference between curves (a) and (b) of both figures is probably due to the fact that the

flow became turbulent when the separated shear-layer was impinged up on

by the high speed jet produce by the narrow slot. In the case of

downstream injection,(curve c), the base pressure reduction was due to

the "ejector effect" of the injection-jet, while the increase of pressure

Ps

was caused by the momentum addition.

Curves (a) of figures6 and 7 (related to upwards injection) are

compared in figure 8. The dotted line, obtained by adding the dynamic

pressure of the secondary air (computed from the flow rate and the slot

area), coincides with the measured base-pressure curve.

*

_{At Cq}

=

0.1, the computation shows that the momentum added into the dead-air region of the flow per unit time is of the order of one third of a percent of the momentum flow through the boundary-layer just before separation.

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, 9 Detailed statie pressure distributions, measured along the eentre-line of model SI-4, are shown in figure 9 for upwards and downstream injection. For small values of the injection coeffieient (C ), it is seen

q

that the base pressure increases with C while the maximum pressure

q

gradient deereases. There is a corresponding downstream displacement of the reattachment region of the main flow associated with the pressure rise. For high values of C ,the,behavior of the flow differs with the orientation

q

of injection. This was attributed to the momentum addition as well as to 'the upstream shift of transition. _,

The d~rection of the flow, near the model surface, was determined by the use of silk threads, 200

mm

long, stretched spanwise across model SI-4 (the threads were eurved in the flow direction). The results are given in figure 10 for upwards and downstream inj eetion . The direction of t'he free-stream is, from' 'right to Ieft. The wind direction on the surfaee is shown by arrows; dotted marks are used to indicate when the threads did ,not'

respand because the velocity was either too smallor equal to zero, and double arrows are related to oscillating' threads. Figure 10 shows the downstream shift of the reattaehment line when C increased from 0 to

q

about 0.1. Above this value, the region of reversed flow disappeared pro-gressivefy.

From this result and the position of the maximum pressure gradient given by figure 9, it was possib1e to draw schematic diagrams of the flow as shown in figure 11.

These were fur~her substantiated by observing the flow on the model surface with a sublim,ation technique as indicated in figure 12. At C :::I 0

q

(fig. 12a) the typieal three-dimensional pattern of tha flow (reported in reference 1) is clearly seen. As C increases, the reattachment region,

q

movè.$ downstream (fig.12a to 12d). For large values of C , the reversed

q

flow disappears (fig. 12e to l2h). It is interesting to observe the indi-vidual three-dimensional aspects of the main flow and o~ the aecondary flow at C

q

=

0.4 (fig.l2f), which form a unique three-dimensional pattern

as C

q becomes larger (f'ig .12 g-h). These surfaee flowpictures are con-sidered to be quite remarkable in showing the consistency of the flow,

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10

because they were obtained over running times of the tunnel of the order of two hours.

It was concluded, from these measurements, that large rates of gas inj e,c,tion in a separated laminar flow have rather complicated effects which are difficult to interpret. However, the flow behavior is mucn more

straightforward for moderate rates of air bleeding as it is independent of the particular technique of injection. The results, summarized in figures 13 and 14 show the large increase of the base pressure and decrea~e of the

.

-maximum pressure gradient for small rates of injection. Identical results were obtained on mode1s 51-3 and 51-4 when plotted versus C (for

q

From these results, it was possible in particular to determine the amount of suction which is equivalent to ~he cross-wind produced by the span effect. Indeed, the 7% decrease of bàse pressure, shown in figure Sp

corresponds to a va1ue of C of about 0.03.

q

Misce11aneous tests

As shown in figure 2, the injection model was assembled by using a clamping plate the nose of which formed a wedge. It was located 200 mm downstream of the step. A test was made to find the influence of that wedge on the statie piessure distribution at reattachment. This was done by installing a shock-generator above the model having tha same wedge-angle as the clamping p1ate. The pressuredistribution was measured on the model for various streamwise positions of the shock generator.

The results are given for C

=

0.6 in figure 15 where the impact

q

point of the shock on the model surface is indicated. It shows that the shock-wave formed on the wedge of the clamping p1ate had no influence on the base pressure and on the pressure gradient at reattachment.

A test was made with injection of a foreign gas (Freon) into the separated region of the flow on model 51-3. The s·tatic pressure ratio

~5 was measured as a function of C

q in the case of upwards injection. The resu1ts are shown in figure 16 and compared with the air injection data.

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11 A considerable difference exists between these results inasmuch as the base pressure decreases for small amounts of freon injection. No explanation was found so far for this difference.

EFFECT OF GAS INJECTION ON TURBULENT BOUNDARY LAYER8

The effect of air-bleeding on the base-pressure has been investigated

in the case of transitional and turbulent separated flows and compared with

the resu1ts of the 1aminar case. The tests were made with vertical injection

on models SI-3 and 8I-4 by instal1ing various tripping devices on the plate

upstream of the step.

In figure 17D the increase of base-pressure in percent of its value

at zero injection is plotted against a non-dimensional flow parameter

de-fined by

where Q1 is the rate of inj ection per unit spanD h the stelP-height~

f

00 the

free-stream density and ~QO the free-stream velocity of sound. This ~~&me

ter is derived from the theoretica1 analysis of reference 12 mainly related

to the case of a thin approaching bounda.ry-layer upstream the step and has

~.

been used here-in for the sake of comparison although the approaching

boundary-layer had a finite thickness.

Figure 17 shows that the base-pressure rise with C is greater for' a

q

turbulent boundary-layer than for a. laminar one. The ratios of momentum~.

thickness to step-height (e/~) are indicated in the figure as well as the

free stream Mach number (Moe)' This ratio was computed at separation (for

the laminar case) from the theory of reference 10D assuming an adiabatic

flat p1ste upstream of ths step. It was computed in ths fu11y turbulent case

from the measured velocity profile. This profile is shown in figure 18 and

compared with the theoretical profile given by

Also shown in figure 17 are the results of reference 11 for a

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12

the theory of reference 12 and indicate a larger effect of air injection than in the present investigation although the ratio of momentum-thickness to step-height was approximately the same. However, in ref. 11 the ratio of model-span to step-height was only equal to 4 compared with 20 for the

present investigation. It is possible, as shown in reference 9, that a

cross-flow existed in the separated re~ion of the flow which shifted the zero value of the injection coefficient towards negative,values (suction).

CONCLUSIONS.

Air_bleeding in a separated laminar supersonic flow increases the

base-pressure and decreases the pressure-gradient at reattachment. This effect is independent of the particular technique of injection for small injection rates. For large rates of injection, the effect of air bleeding d'epends strongJ,y upon the manner of inj ection.

The effect of air injection in a turbulent separated flow is to in-crease the base-pressure in a stronger manner than in the laminar case. However, this effect was found to be smaller than theoretically predicted.

When freon gas was injected, it produced the opposite effect namely of decreasing the base-pressure at low rates of injection.

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REFERENCES

1. J. Ginoux Leading-edge effect on sepsratea supersonic flows -TCEA TN 4, May 1961

~. S .M. Bogdonoff and 1. Vas ,

Pre1iminary investigations of spiked bodies at hyper-sonic speeds - J.Ae.Sc. vol 26, nG

2, pp. 65-74,

February 1959

3. Dean R. Chapman A theoretica1 analysis of the heat-transfer in regions

of separated flows - NACA TN 2792~ October 1956

4. Howard K. Larson Heat transfer in separated flows - I.A.S. preprint,

report ne 59-37

5. T. Sprinks A review of work relevant to-the study of

heat-trans-fer in hypersonic separated f10ws ~ University of

Southampton~ U.S.A.A. Report n° 138, June 1960 6. J. Ginoux The TCEA continuous supersonic wind tunnel S-1

-TCEA TN 1, October 1960

7. J.F. Nash Laminar separation in su~ersonic flow with emphasis

on fluid injection - Student project thesis, TCEAá

July 1960

8. S.O. Han Preliminary study of the effect of gas injection in

a 1aminar separated supersonic flow - Student project

thesis, TCEA, June 1961

9. J. Ginoux On the existence of cross-flows in separated supersonic

streams - TCEA TN 69 F'ebruary 1962

10. D.R. Cha~an and H. Rubesin

Temperature and velocity profiles in the compressible

1aminar boundary-1ayer with arbitrary distribution of

surface temperature - J .A.S., vol. 19, September 1949

11-. M. Sirieix Pressi.on de culot et processus de mélange turbulent

en écoulement supersonique plan - La Recherche

Aéro-nautique n° 78, 1960

12. H.H. Korst, R.H. Page and M.E. Childs

A theory for base pressures in transonic and

super-sonic flow - University of 111inois, TN 392-2,

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lO 10 ~"'

,.

1

120 5 5 L H ;::; 2.21 <]00 Nodel SI - 3 l10del SI - 4 L = 220 mul L ;::; 115 mm h=lOmm h :: 10 mm

Figure 1 - Model configuration

Tunnel w,g,ll

---- - -

---=-==:.=.::--.:.:.==---base-pressure M=2 .21

<]:::::==

.---=-_ .---=-_ .---=-_ .---=-_ .---=-_ .---=-_ .---=-_ .---=-_ -L.. _ _ _ --'-_ _ _ _ _ _ _ _ _ _

v

..

_(})

from dry er lIIIIi

ThrottJ.ing flow atmosphere

valve meter pressure

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.

~

--

~

.<'

•• >~ I

f

A5~

-

(22)

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18 ' .!-~_.

17

V m/sec

IZZ

-r

., 5 f - I

l f I + f I + + + f I

-141 ." t , I , , ' , I I I

-sa

-40 -30 -20

-Ia

,0

la

20

30

40

sa

60

~~

Q

=

99 l/min (standard atmospheric conditions)

Figure 4 - Spanwise survey of the flow in the injection slot

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l.~---.---r~~---~---' .95 ~---r---r~--*---~ .90~---~---~---+--~---~

o

With fences .85

o

Without fences .80

.

7

5

Equivalent suction • 70 ~---~

."3t

-~---.65 1---+

4

+---~~---~ .60 ~---~

o

.55 5

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l~OOr'--Iï--~--~--~--.---r--'--~--~---p

pao

fence _lh.L... __ .90

-

__ '- _ _ --~,,""" s

.--~

.-'-nnn

0

.80 tnfll" .70 .50 / / / - - - I

.<.;/ ...

---,::'/ .40\ I I I I I I

o

.2 .1.. .6 .8 Cri 1.0 1.0

P

Pa?

o

short fences 106 mm .90

o

long fences 200 mm

~o

.8 .60 .50 .401

ucr~

--~--

~Ar---~'~[~.~rrlr~~---1--~I'~I--ll--~

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1. OOI---t---T---t---r---r----,---+-~--.---,

PS"

Pro

.90 .80

.70

.60 .50 • 40

o

[> S=7 mm }

upward.s inj I..~C tion s

=

2 mm downstream injection (a)

~

(b) (c) [>

MODEL SI-4

1.0 1.00

P5"

Pro

.90 .80

.50

~~~~~~~~~~I

o

[> short fences 106 mnl long fences 200 mm with comb (d)

,"",_n

\-

-H'----v--'-'

MODEL 81-3

.40 I I I I I I I .

o

.2 .4 .6 .8 Ca 1.0

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.90rj---

---,---r---r---r---~---Pb

Ij

PS"

f:>()O

poo

.80

HODEL

SI-4

upwards injection of air

/,9--~

/ / ' .701

~~

/

~

.4

/ /

....-:/~

°

.6

/ , , 0 /

SJ""""---•

/ .,,/" .,/'

/~

°

base-pressure

Fb

•

pressure

_p'>'

/

/ /

EY2.

2. °

pressure

P5

+

dynamic pressure

.8

1.0

Figure 8 - Comparison bet\-leen pressures

!->b

and

PS"

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.00

p=E

rIF

KEY ~5

c

= 0

0

q

•

.025

0

.049 .90

•

:083

0

.102 .85

•

.209 'Ç1 .327 .80

.75

\ j - - - _ - - ! .70

O---_ _

- - l .65

G - - - - _ - - L L

e _ -_ _ _

_

MODEL SI-4

.60 _{I - Upl-lards} _injeetion

.55

o

5 10

Y../

_h 15

(34)

(35)

KEY 1.00

O

·c

_C

₌

_.41 q

•

.53 .95

0

.65

•

.93 • 90

<J

1.06 HODEL SI - 4 .70 ]; - Continued

~---~---

_

~I~---~~

o

5 ~O iS Figure 9 - Continued

(36)

(37)

.00

p=e

_f>co

.95 KEY

0

C :::: 0 q .90

•

.05

0

.09 • 85

•

.14

<J

.21 .80

.75

<l---~ .65 Model SI-4 .60 11 downstream injection

o

15

Figure 9 - Continued

(38)

(39)

1.00

F==

E

_~

F.EY .95

0

C q

=

.28

• .

44

0

.53 .90

111 .74

0 .97

.85 .80

.75

.70

l10del SI-4

Ir -

Continued

.

550~---~--~5~---~---~'---~

₁₀ _x/h _.5 Figure 9 - Concluded

(40)

(41)

C_q

=

0 7 ' 7

r

,-

....

I ' l" .26

I

)

--,

/ I I

r,.

I ? /

,7

, I -=c-,

I

r--I

,

J-

7

.36 ~

I

/

_I

,.

_I

~,

_I~

I~

_I

? ;

I ~ -r / 7

I

'"' :;:: 0

~

'"'

I

9

,

7 7~

!

I~

1 I

7

r

7 ,

77 I

'

11~

.05 ,. < )

rt~

I

,

"7

I i ...

Ir:?j

19"

-::1---; I I

7

I

7

I

.11 _<. _i _{E i}

=;-,tr

I

,

_I

>

_I

I . 9 "

ç:==;

-,

-

-,-I

,

I

/

I _I I .19

?,

,tV

I 7 _/

I~

_/

-;1;

_/

( T-

7 r-

I

'r-

,

-/ I

7

7 _I .29

-,-- tV

I

/

PI

I

;7

'7

ry

I

/~l

-r-~

- r

I I _I

I

_I

I

₇

,.

/

) .39

,-tV

I

07 TJ

I

' 7

,

r

j ï ~

₇

,

7

--1:-7

7

I /

.49

Jt-r

c "

?;4

1V

I

,

7 I I

,"'7'

7

Pi

I~

_;

7=)

₇ -.,. "0

'-+/tr

o

:

Î

· '

~

_{? ,}

_7~

. . I

?

0Ii' I

I

,.

/

I

_/

I

_/

u~rARDS

INJECTION

(42)

(43)

No injection ./" upwards injection small C_q

7

7 large Cq

_{) 7 /}

₇

J

/

J

>

'

,

7

larg_e_c_q _ _ _

-~

?

7

?

_____

~==S!=sy

;

_"

)

₇

,

₇

>

_I

>

_I

;

/

,

(44)

(45)

a) c

=

0

q

b) c

=

0.1

q

(46)

.

_.

(47)

c) d) c

=

0.17 q c

=

0.22 q FIGURE 12 - Continued.

(48)

..

,

..

/'

,~

(49)

e) c

=

0,32

q

f) c

=

0.40

q

(50)

(51)

g) c

=

0.56 q

h) c = 1.0

q

(52)

, _,

(53)

4·0 30

_;f

~ pressure-gradient ~ at t:eattachment ( model 8I-4)

o

20 -~o Base-pressure 10

o

Model 5I-3

o

Model SI-4

o

°2

Figure 13 - Variations of the base-pressure and pressure-gradient

(in percent) with the injection coefficient C_q

(54)

(55)

1.0

~

O~.

_~

~

KEY

o··i

_'V

• Pro

₀

_c

₌ ₀

O··i~

_I

~.

0 'V

q

•

• 005

o.O~'V!

0

.011

•

• 017

•

.90

~

0 t>

.~

0

• 025

• •

'V

6

•

• 033

o

•

[> _•₀₄₄

. _ t>

~ ~

•

• 055

00 .\7

6

•

\l • 083 0 • •

~<3

~ • 111

t>

'V

6 ....

Iè, _{• 139}

·0.

.80

•

• 1(,7

o

~.

• •

4~

<J

• 222

₀

[>\7.

....

• 278 O~

<J

.

O.

~

·t~~

~~~~~4~:il

.70

<1<1<1<1<1<1<1;

•••••••

6 6 6 6 6 6 g

~~~~~~m

\7\7\7\7\7

···t

MODEL SI-4 t>[>[>[>[>~

....

;

UFWARDS INJECTION

0000

~~~~

• 60

••••

0

0 0

10

_xI

5 h

(56)

(57)

.90

Pipa:'

~

.86 .82 -I '

.

~

/~I

shock shock

.78

F\"

impact impact

î

~

0 5 10 15 x/h

Figur.e 15 - Effect of a shoc~·wave on the statie pressure distribution •

.

80~1----~---'---'---.---r----~----~~----r---~---r----~

Po;p~

o

AIR

.70

.60

r

~.

G

• .-=t:"""::-o

.2 .4 .6 .8 C~ 1.0

(58)

(59)

120

~lent

l:\Pb

t

100

•

ONERA turbulent (

~

::: 0.027 .MQO=2.21 ) 80

•

60

j

Transitiona1

/

40 20 (

~

:: 0.014 j

1'\,0

= 2 • 21 ) I I

o

('7' 100 '5 120 ~x 10

o

20 L~O 60 80

(60)

(61)

1.0

.8

o

measured _ _ computed .6

*~

=

(~)

'11

.4

.2

o

0 o

o 8 1₀0

(62)

(63)

TCEA TN 7

Training Center for Experimental Aerodynamics.

EFFECT OF GAS INJECTION IN SEPARATED

SUPERSONIC FL{)tlS

February 1962 Jean J.Ginoux

An experimental investigation has been made at a Mach number of 2.21

on the effect of air injection in

separated supersonic flows using

two-dimensional backward facing step

models. This effect, in a laminar

flow, was found to be independent of

TCEA TN 7

Training Center for Experimental

Aerodynamica.

EFFECT OF GAS INJECTION IN SEPARATES

SUPERSONIC FL{)tlS

An experimental investigation has

been made at a Mach number of 2.21

separates supersonic flow8 using

I. Ginoux,Jean

Il. TeEA TN 7

I. Ginoux, Jean

11. TCEA TN 7

the particular technique of injection when the rate of

injection Was smalle Air injection raise. the base

pressure and decreases the pressure gradient at

reat-tachment. At high rates of injection, considerable

differences are found between the result. obtained for

various techniques of injection. It was also shown that

the increase of the base pressure is larger in the

turbulent case than for a laminar boundary-layer. When

freon gas was injected, it produced the opposite effect,

namely of decreasing the base pressure at low rates of

injection.

(copies available at TCEA - Library)

injection was smalle Air .injection rai.ea the base

differences are found between the results obtained for

various techniques of injection. It was a1so shown that

the incr . . se of the base pressure is larger in the

freon ga. wa. injected, it produced the oppoaite effect,

namely of decreasing the base pre •• ure at low rate. of

injection

(64)

TCEA TN 7

Aerodynamic8.

EFFECT OF GAS INJECTION IN SEPARATED SUPERSONIC FLaJS

February 1962 Jean J.Ginoux An experimental investigation bas

two-dimensiona1 backward facing step models. This effect, in a laminar

TCEA TN 7

Aerodynamic ••

EFFECT OF GAS INJECTION IN SEPARATES SUPERSONIC FLaJS

February 1962 Jean J.Ginoux An experimental investigation has

separates supersonic flows using two-I

dimensional backward facing step

I. Ginoux,Jean

Il. TCEA TN 7

I. Ginoux, Jean

11. TCEA TN 7

the particular technique of injection when the rate of injection was smalle Air injection rai.es the baae presaure and decrea.e. the prea.ure gradient at

reat-tachment. At high rate. of injection, con.iderable

difference. are found between the result. obtained for varioua techniques of injection. It wa. also shown that

the increase of the baae pressure ia 1arger in the turbulent case than for a laminar boundary-layer. When

freon gas was injected, it produced the oppoaite effect, namely of decreasing the base pressure at low rates of

injection.

(copies available at TCEA - Library)

injection waa amall. Air ,injection raises the base

pressure and decreases the pres.ure gradient at

differences are found between the results obtained for various techniquea of injection. It was a180 shown that

the incr . . . e of the ba.e pressure ia larger in the

turbulent case thanfor a laminar boundary-layer. When freon gas was injected, it produced the opposite effect,

namely of decreasing the ba •• pre.sure at low rates of

injection

(65)

~

TCEA TN 7

Training Center for Experimental Aerodynamics.

EFFECT OF GAS INJECTION IN SEPARATED SUPERSONIC FLClJS

TCEA TN 7

I!aining Center for Experimental A erO'aynamic ••

EFFECT OF GAS INJECTION IN SEPARATES SUPERSONIC FLClJS

I. Ginoux,Jean Il. TCEA TN 7

I. Ginoux, Jean Il. TCEA TN 7

the particular technique of injection when the rate of injection was smalle Air injection raise. the ba.e pressure and decreases the pre •• ure gradient at

differences are found between the result. obtained for

various techniques of injection. It wa. also shown that

the increase of the base pressure is larger in the

freon gas was injected, it produced the oppoaite effect,

namely of decreasing the base pres8ure at low rates of

injection.

(copiea available at TCEA - Library)

injection was smalle Air ,injection rai.es the base

differences are found between the results obtained for

various techniques of injection. It was also shown that the increase of the base pressure is larger in the

turbulènt case than· for a laminar bounciary-layer. When

freon gas wa. injected, it produced the oppoaite effect,

namely of decreasing the base pres.ure at lew rate. of injection

I,

' I ' L . - . . . - - - . - J

separates supersonic flows using two-'

dimensional backward facing step

(66)

TeEA TN 7

Aerodynamic ••

EFFECT OF GAS INJECTION IN SEPARATED SUPERSONIC FL<JJS

February 1962 Jean J.Ginoux An experimental investigation has been made at a Mach number of 2.21 on the effect of air injection in

separated supersonic f10ws using

two-dimensional backward facing step modeis. This effect, in a 1aminar

flow, waa found to be independent of

TCEA TN 7

Aerodynamic ••

EFFECT OF GAS INJECTION IN SEPARATES SUPERSONIC FL<JJS

February 1962 Jean J.Ginoux An experimental inveatigation has been made at a Mach number of 2.21 on the effect of air injection in

separates supersonic flow. using

two-dimensional backward facing step models. This effect, in a 1aminar

I. Ginoux,Jean

! I . TCEA TN 7

I. Ginoux, Jean

11. TCEA TN 7

the particular technique of injection when the rate of injection wa. amall. Air injection raiaea the baae pressure and decreaae. the pre.aure gradient at

reat-tachment. At high rate. of injection, conaiderable

differences are found between the re.ult. obtained for various techniquel of injection. It waa alao shown that the increale of the bale preslure il larger in the turbulent case than for a laminar boundary-layer. When

freon gas was injected, it produced the oppoaite effect, name1y of decreasing the base pressure at low rates of

lnjection.

(copiea available at TCEA - Library)

injection was smalle Air .injection raiaea the base

presaure and decrea.ea the pres.ure gradient at

reat-tachment. At high rates of injection, conaiderable

dlfferencea are found between the results obtalned for various techniquea of injection. It was also shown that

the incr . . ae of the baae preisure ia larger in the

turbulent case than · for a laminar boundary-layer. When

freon gaa waa injected, it produced the oppoaite effect,

namely of decreallng the baae prelaure at low ratea of

injection