Leading edge effect on separated supersonic flows

-TECH

' HE H G' (",DOL

DElFT

VLiEGTUIGBOUWI"'Ut DE Michiel de ~uyterweg 10 - DElFT

l' aug.1961

~ TRAINING CENTER FOR EXPERIMENTAL AERODYNAMICS '

z

l-c( LIJ U

I-LEADING EDGE EFFECT

ON SEPARATED SU PERSONIC FLOWS

BV

1.1.

GINOUX

Rhode- Saint-GenKe. Belgium.

MAV 1961

MONITORING AGENCY DOCUMENT NR. ASTIA DOCUMENT NR.

TÇEA TN 4

LEADING EDGE EFFECT ON SEPARATED SUPERSONIC FLOWS by

Jean. J. Ginoux

Brussels University and TCEA

CONTRACT NR. AF 61 (052) - 350 -LAMINAR SEPARATION IN SUPERSONIC FLOO

TECHNICAL NOTE NR. 1 May 1961

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

FOREiWRD

The au thor would like to thank the European Office of the Office of Aerospace Research (EOAR) for the sponsorship of this work and also to

record his thanks to CNERA, without whose support this pro gramme of research would not have been started, and from which the author has received every

NOTATION

x distanee a~ong the eenter-line of the model from the step base; x7 0 downstream of the step and x

<

0 upstream of the step

y z Po p Pp ~Pp h S L €'W\, (j.~ B

distanee perpendieular to the surfaee of the model (from the probe-axis)

span-wise axis, positive as indieated in the figure

boundary-layer thiekness

wave-lergth of the flow perturbations stagnation pressure

statie pressure pitot-pressure

span-wise pitot-pressure variation expressed as a fraetion of the pitot-pressure measured on the eenter-line of the model

differenee in

D.p

_{p bet\17een a pressure peak and its neighbouring} pressure va11.ey

step-height model span

leng th of the plate upstream of the step mean leading-edge thickness

maximum loeal variation of the leading-edge thickness (i.e. maximum differenee between neighbouring peaks and troughs)

1 ...

SUMMARY

Follmving earlier tests (ReL 1), in the T.C.E.A. supersonic tunnel S-l (Ref. 2), on a two-dimensional backward-facing step model in which span-wise perturbations were found in the reattachment region, further

studies have been made using the same and other similar models. In these later studies, the same three-dimensional perturbations were detected, into the full thickness of the boundary-layer, af ter reattachment, both in

turbulent and laminar regions of the flow. Their amplitude was a maximum in the transition region.

Using a model with a much improved accuracy of manufacture,

notably at the leading-egde, it ,,,as found that the amplitude of the perturb·' ations was greatly reduced, roughly in proportion to the size of the

irregularities of manufacture of the leading-edge itself. As it is

unrea-. sonable to expect these to be anything other than random in character, it is concluded that the phenomenon is essentially one of instability in the two-dimensional flmv, the main triggering action arising, at least in the earlier tests, from small irregularities in the leading-edge.

INTRODUCTION

In the course of a research programme undertaken at T.C.E.A. on laminar separated supersonic flow, the au thor found that three-dimensio-nal perturbations existed in the reattachment region of the flow over

bac~"ard-façing steps (Ref. 1). The periodical span-wise distribution of these perturbations could not be explained by irregularities either in the air-flow upstream of the models or in the models themselves. Surveys made with total-head probes moved in contact with the model surface showed that,

at a Mach number of 2.16, the ratio of the wave-length of the flow pertur-bations to boundary-layer thickness was a function of the ratio of step-height to boundary-layer thickness, independent upon the span of the model.

In a continuation of the work, span-wise surveys were made at various heights in the boundary-layer in the reattachment region of the flow as well as upstream of the step, in the separated shear-layer and in the transition region. More attention was given to the amplitude of the span-wise pressure variations. The study was completed by a detailed analysis of the influence of leading-edge irregularities on the intensity of the flow perturbations.

DE8CRIPTION OF EQUIPMENT

Wind Tunnel

The tests were made in the T.C.E.A. 40 x 40 cm2 (16" x 16") continuous supersonic wind tunnel 8-1 at a Mach number of about 2.16. A description of the tunnel is given in reference 2.

Model configuration

8everal backward facing step models were used in the present investigation. They are shown in Table I, where h is the step-height, L the length of the plate upstream of the step, 8 the model span, given in millimetres; B~ is the mean leading-edge thickness in microns (i.e. 10-3 mm) and

/J.'t,

the local vàriations of the thickness (in microns). Models 8-20, having a span equal to 200 mm could be fitted with end-piates denoted by the symblol B. Models 8-6 and S-20, which did not span the 400 mm test section, were mounted symmetrically in the center of the test section.

3.

Table I

Model configuration and designation

!

I

Model L h 8pan,8 ~.M. b.~ max

(rom) (nnn) (nnn) (microns) (microns)

8-3 225 10 400 72 10 8-6 60 3 150 13 7

I

S-20-c -(B) 80 6 ' 200 224 3

I

S -20-e- (B) 80 7 200 165 20

I

I

S-20-f-(B) 80 7 200 96 3

I

Surveying mechanism

A sting-support rig, allowing for displacement of probes in three directions was incorporated in the diffuser. It consisted of an axial tube

(1.1 m long) supported by two vertical screws (having a 2 mm pitch), the axes of which passed through the upper wallof the tunnel. Their motion was

controlled by reversible electric motors, the revolutionsbeing recorded on counters (one revolution of both counters corresponded to a probe displace-ment of 0.054 mm). Both screws could be rotated independently to allo\-l a vertical translation of the sting as well as a rotation about the center of

the test section (+ 7 degrees). The sting could slide inside the axial

tube; this longitudinal motion was controlled by a reversible electric motor, located in the air-stream at the back-end of the tube, and having a total range of displacement of 50 cm, one revolution of the counter corresponding

to a 1/20 mm displacement of the sting. In addition, the test section could be traversed horizontally along a 150 mm length by fixing a special head to the sting. This consisted of a horizontal slotted wedge having a 180 mm span in v/hich a carriage could slide. The motion \vas controlled from outside the tunnel by a flexible drive fitted with a revolution counter. The support of the probe was swept fonvard and fastened to the lower surface of the carriage in such a manner that the nose of the probe was located upstream of the leading-edge of the wedge. The ,,,edge ,,,as adjusted in such a way that the nose of the probe could be moved parallel to the model surface during the span-wise surveys.

Test technigues

Transition from laminar to turbulent flow was detected on shadowgraphs and schlieren pictures, taken with a conventional 0 ptical system, using parabolic mirrors and a spark light-source.

The flo,,, on the surface of the models was qualitatively observed by the use of a sublimation technique. The indicator chosen was azobenzene, which having a slow response, allowed for the relatively long starting and

stopping times of the wind-tunnel. An indication of the surface-flow pattern was generally obtained af ter 3 to 6 hours running time (depending upon the

thickness of the azobenzene layer and the tunnel pressure).

The boundary-layer was surveyed, at different locations (x) from the step, in the span-wise direction (z) and vertically (y), with total head probes of various sizes, fixed to the surveying meehanism already

described. The pressure vlas measured by a differential pressure piek-up and a Brown recorder.

Statie pressure distributions were measured along the center line of the models with a mul ti tube manometer using silicone oil.

The leading-edge of the models 'tV'as examined with a microscope. Each model was mounted vertically on a machine-tool table with its

leading-5.

edge horizontal. A microscope with a magnification of 150 or 300 't~as

trans-lated so as to cover its span. Under the microscope, the leading-edge

appeared as a thick band whose coordinates were taken at increarnents of

0.1 mm over a portion of the span. The accuracy of the measurements was about 1 to 2 microns, depending upon the magnification.

DETAILED SURVEY OF THE BOUNDARY-LAYER FL~v ON MODEL S-3

A detailed survey of the boundary-layer flow 't~as made at a

Mach number of 2.16 and at a stagriation pressure of 170

mmoc

mercury absolute

on model 8-3 (table I) which had a 10 mm step-height and a flat p1ate length of 225 mm upstream of the step. The model comp1etely spanned the working

section of the wind-tunnel. Using the surveying mechanism, transverse

pitot-pressure profiles were recorded a~ different heights in the boundary-layer

and at several distances from the step base; only a portion of the span was

surveyed (from z

=

0 to z

=

60 mm, except in the separated layer where

o <

z

<

40 mm).

The span-wise pressure variations are expressed as a fraction

of pitot-pressure measured on the center-line of the model (z = 0) using the

fo1lowing relationship

the axes x, y, z being defined as shown under "NOTATION". The results of

vertical surveys made at z = 0 for different values of x are shown in

figure 1, they were used to define the reference pressure Pp (x Y 0), as

well as the boundary-layer thickness (

& ).

The static pressure distribution

along the center-line of the model is given in figure 2.

The results of span-wise surveys are shown in the various graphs of figure 3. The measurements made downstream of reattachment (i.e. for x larger than about 70 mm) indicate that the flow perturbations, previously

detected in the vicinity of the model surface (Ref. 1) extend into the full thickness of the boundary-1ayer with a maximum variation of pitot-pressure occuring at about mid-thickness, the perturbations in pressure vanishing as the outer edge of the boundary-layer is reached. In the surveys made at

x = 81 mm, two different cylinder probes were used, having inside diameters of 1.5 mm and 0.25 mm and outside diameters of 2 mm and 0.3 mm respective1Yj similar resu1ts were obtained for both probes as shown in figures 3-9 and 3-10.

The fact that periodica1 transverse total-head variations were found at various heights in the boundary-layer ~vas an indication that the boundary-layer profile (pressure against height) was periodica11y distorted a10ng the span of the model. This was confirmed by direct measurement of these profiles at different va lues of z. The measurements were made at x

= 81

mm in a region (for 30

<

z

<

40 mm, with increaments D.z

= 1

mm) where the 1argest pressure variation was measured in the z-direction. The

results are given in figure 4 where the pitot reading, in mi11imetre of mercury, is plotted against y; no attempt was made to reduce these data to velocity profiles, as it was possib1e to measure the wall statie pressure only on the center-line of the model. There was therefore no evidence that the statie pressure cou1d be taken as constant along the z-direction. From these results, i t was possib1e to evaluate the boundary-layer thickness as a function of z; as expected, it ~vas found to vary periodica1ly; as seen in figure 4. Simi1ar results were recent1y obtained at low speed by Schubauer (unpublished) •

Surveys were made in the separated boundary-layer at x

= 16 mm,

x

= 45,

.2 mm and x

=

63.2 mmo The nose of the probe was bent in order to be a1igned with the flow direction (see figure Sa). The results shown in figure (3-11) indicate that the flow perturbations were mainly localized in the inner portion of the shear-layer (i.e. for y 1ess than about

~

/2).

Measurements made upstream of the step at x

=

-5 mm, -55 mm and -105 mm (figures 3-6 to 3-8) a1so showed the existence of three-dimensiona1

7.

perturbations. The variation of pitot-pressure had its maximum value at about mid-thickness and vanished near the outer edge of the boundary-layer. They also vanished near the model surface, which explains why they were never clearly detected in the early part of the research (Ref. 1), either by a probe which was moved in contact with the model surface or by the sublimation technique.

Figures 6a-b give a summary of the results. For each x, one value of y/b for which the amplitude of the pressure variations was maximum was selected among the available data of figure 3. These values of y/b are

indicated in the upper part of the figure which represents a cross-section of the model (plane x-y) and the corresponding span-wise pressure variations are shown in the lower part of the figure which gives

.6.P

_{p (in} %) as a

function of z (for 0

<

z <.60 mm, except in the free layer for 0

<

z

<

40 mm)

These figures show that three-dimensional perturbations existed upstream of separation (x

<

0) although they were rather weak; a maximum variation b,'Pp of about 6 % was found between a pressure peak and its

neighbouring pressure valley. As the boundary-layer separated and reattache~,

the perturbations were progressively amplified to reach a maximum amplitude in the transition region (

b'pp

= 44 %). They were then extending in the

_,

. turbulent region of the flow, being slowly damped ( D,.

\'>p

= 8 % at

x = 164.5 mm). It will be noted that the perturbations were not indicated in that region by the sublimation technique (Ref. 1).

A close observation of figures 5 (with the help of figure 3 where large

6.p

_{p scales are used) shows that the z-position of the peaks and} valleys did not vary with x. This is quite clear af ter separation but not

50 clear upstream of separation because of the very small amplitudes of most of the perturbations. On the other hand, the repeatability of the measure-ments was not as good for x

<

0 as for x/"O and some of the small pressure

peaks were not well defined; this is shown in figure 3-12 where different probes were used.

It appears from these results that \l7eak perturbations existed in the boundary-layer before separation, but their amplitude is much greater, they follo\17 a much more regular pattern and in detail they are more repeatable af ter reattachment.

In reference 3, Hopkins presents photographs of various models coated with fluorescent oil which show evidence of surface vortices at a Mach number of about 3. Some photographs are also presented for the models

coated with a sublimation material as \l7as used in the present research. They show that the flow perturbations are more clearly indicated by the fluorescent

/1 /1

oil. In particular the vortices are visible at a small distance behind the leading edge (i.e. upstream of separation) and it is observed that their spacing increases with the distance from the leading-edge, which is in agreement ,·dth Görtler's theory (Ref. 4) derived in the 10\17 speed case. The boundary-layer surveys made in the present work did not reveal such a variation of the spacing of the perturbations; it is possible that the probe

was not sensitive enough to detect the smallest perturbations.

LEADING-EDGE EFFECT

Evidence was given from the results of the detailed surveys made on model S-3 that the regular pattern of three-dimensional perturbations that existed at reattachment was triggered by the weak perturbations observed in the boundary-layer upstream of separation. The problem was then to find a reason for the existence of these perturbations. In the early part of the research (Ref. 1) it was found that irregularities in the leading-edge of the model could not explain a regular pattern of perturbations. However, not much attention was given at that time to the intensity of the perturbations and it was therefore decided to re-examine the leading-edge effect more carefully. In a series of preliminary tests, several models were tested

with accidental or wilful damage in the leading-edge which indicated a strong modification of the intensity of the perturbations. These results finally led to a more systematic investigation during which the effect ot of the machining accuracy of the 1eading-edge was examined.

9.

Preliminary Tests

Figure . .la' is rela ted to a boundary-layer survey made a t x

=

-155 mm (i.e. 70 mro downstream of the leading-edge) on model S-3, in the presence of an accidental notch in the leading-edge, whose approximate size is indicated. It shows that additional and strong three-dimensional pertur-bations were introduced in the boundary-layer by that notch. Their amplitude \-las approximately ten times as large as that of the amplitude

I

of the perturbations usually detected upstream of separation ( ~~p

=

60

%

instead of 6

%).

Taking into account the size of the notch, it might

be expected, by simple proportionality, that an indentation la times smaller would produce perturbations of the same intensity as the ones usually

observed (6

%)

that is for a characteristic dimension of the notch of the order of 1/100 mm or less. This \-las precisely the accuracy of the leading-edge of the various models that were used in the present research. An example is given in figure 8 (a-b), where the leading-edge thickness of model S-3 is given against the z-coordinate, as determined by a microscope;

the vertical scale is enlarged by a factor of 500 over the horizontal scale, hence the saw-tooth appearence of the leading-edge.

Similar results are shown in figure 7b also related to model S-3. A notch approximately 40 microns deep, introduced a local change in

bp

_p of about 22 %.

The leading-edge effect was further examined by testing model S-6 (table I) which had a smaller leading-edge thickness than model 8-3 (13 microns instead of 72 microns). Model 8-6 which had a span equal to 150 mm

and a step height of 3 mm, vlas tested witli artificial irregularities in the leading-edge thickness. This wás. done by painU~g ".the lower surface of . the leading':"'edge \-ledge along a small portion of the span, very closë to thë leading-edge itself. Thè" bOundary-layer was surveyed at x

=

-25 mm and

+ 44 mm with an without that "thickness element". This is shown in figure 9; the corresponding leading-edge geometry is given in figure la. Figure 9 shows that the thickness element introduced addi tional and st,rong

pertürbations in the boundary-layer. At x

=

-25 mm, a local change of

Óp

_p of 12 % was recordeq., while ü: was equal to 45 % af ter reattachment (i. e. at x

=

44 nun). The 10ca1 increase in leading-edge thickness was of about 20 microns, with the thickness element •.

Effect of the machining accuracy of the leading-edge From the results of the preliminary investigation, it seemed possible to conclude that the regular pattern of perturbations detected in

~

the boundary-layer at reattachment was triggered by leading-edge irregula-rities. In thereconditions, these irregularities should be smaller than

1 to 0.5 micron to maintain a two-dimensional flow within one percent assuming na other influence such as possible free-stream irregularities. In order to check these results further, it was decid~d to imprave the machining accuracy of the leading-~e of the models and observe its effect on the flow pertur-bations.

'With the available machine-tools, this was possible only by using smaller ~odels. The length (L) of the flat plate, upstream of the step, and the span (8) were reduced to 80 mm and 200 mm instead of 225 mm and 400 mm respectively.. The step-height was accordingly reduced to 6 or 7 nun, instead of 10 nun. In these circumstances, two identical models (except for the step-height) were machined which had a mean leading-edge thickness of 224 and 96 microns respectively, with an accuracy of 3 microns. As na straightforward

comparison could be made between the results obtained on these ~10 models and those already recorded on model 8-3 (because of its different size), a third identical model was machined with the usual accuracy of 20 microns; it had a mean leading-edge thickness of 165 microns. Finally, provision was made to fix two small plates to the sides of the models, to check the influence of the reduced span. The configuration and des!gnation of the _{, .} models ,are glven in Tabfé I· (series 8-20) J the existence of side-plates

being denotes by the symbol B. The mean thi.ckness ( ~1t\. ) of the

leading-edge is indicated in microns, as well as the.magnitude of the local variation of thickness (

IJ.

t ).

Discussion of the results

All the tests were made at a free-stream Mach number of 2.16 and a tunnel stagnation pressure of 150 mm Hg absolute, for which transition was located downstream of the reattachment region of the flow as shown by the schlieren pictures (figure 5-b). Total-head transverse surveys were made in the boundary-layer at a distance x

=

69 mm downstream of the step base. A flat probe, higher than wider (outside dimensions 1.9 mm x 1 mm) was used which was more sensitive to detect the flo\17 perturbations than the usual

cylindrical probes; it was kept in contact with the model surface during its motion. The flow on the surface of the model was examined by the use of the sublimation technique and the geometry of the leading-edge was observed with a microscope.

Model S-20-e was tested under these conditions with and without the side-plates (B). The results are compared in figuresll.l and 11.2. The removal of the side-plates influenced the perturbations, inasmuch as

their amplitude decreased by about 5Q

%.

It also resulted in :an increase of the base pressure {as measured directly or as sho\vn by the position of the expansian fan on the schlieren pictures; figures S-b and 5 -c) and in a decrease of thepitot-pressure measured on the center-line of the model at x

=

69 mmo This proved that a certain amount of air was injected in the separated flow from the sides of the model when the side-plates were removed.

With the side-plates, the local variations of À~E' measured between a pressure peak and i ts neighbouring valley, varied bet\l7een 20 and 54 %, with a mean value of 25

%.

The leading-edge geometry is shown in figure 8-c;

its mean. thickness was 165

±

45 microns over the entire span of the model and loeal variations in thickness were of about 20 microns at most. Assuming that the flow perturbations were triggered by leading-edge irregularities, the latter should be of the order or less than 1 micron to maintain a

two-dimensional flow within one percent. These results agree quantitatively with the conclusions obtained from testing model S-3 and were therefore

of the leading-edge.

Figure 11 (1 and 2) also shows that the wave-length of the flow perturbations was not affected by the removal of the side-plates (that is by the model span) verifying the conclusions obtained in reference 1. The distance between successive peaks of the total-head distribution varied between 3 and 6 (figure 11), with a mean value of 4.2 mmo

Flow perturbations are also shown in figure 12 for models S-20-e and S-20-e-(B) where regions of high sublimation rates correspond to dark areas. It is easy to see that the wave-length is the same on both models and also that the perturbations are stronger in the presence of side plates. Note that the leading-edge plate \o1as not coated with azobenzene, but only

the surface on which reattachment occurred, to avoid a modification of the roughness of the surface.

Models S-20-f and S-20-c have been tested under the same conditions as model S-20-e. The amplitude of the perturbations was again reduced by the removal of the side plates. Only the results obtained with the side-plates are sho.m in figure 11 (3 and 4) and compared \vith the pressure variations measured on model S-20-e-(B) at the same value of x (i.e. 69 mm). It is seen that the amplitude of the flow perturbations has been drastically reduced. The mean value of the local change in

L1Fr

was indeed reduced to about 6.5

%

for both models instead of 25

%

on model S-20-e-(B), as the local variations in leading-edge thickness were reduced to 3 microns instead of 20 microns on model S-20-e-(B). Assuming proportionality, and that no other effect than that of leading edge irregularities, it is to be expected that a two-dimensional flow could be maintained within 1

% (

~rp

=

1

%)

if

the ~ding-edge irregularities were smaller than 1 to 1/2 micron.

Figures l2-c and b show the striation pattern obtained on the

surface of models S-20-c and S-20-f by the sublimation technique. Comparison with figure l2-b shows that the amplitude of the perturbations was reduced.

13~

The wave-length of the flow perturbations was measured on the pressure distributions of figures l2-c-d. It varied between 3 and 6 mm on model S-20-f-(B) and between 2 and 6 mm on model S-20-c-(B), with mean values of

4.4

mm and

3.8

mm respectively. Therefore, within the accuracy of measurement, the wave-length remained unchanged (about

4

mm) as the intensity of the pertubations was reduced by improving the leading-edge accuracy. The observation of the models with the microscope never revealed a regular distribution of leading-edge irregularities. Furthermore, the leading-edges of greater accuracy were machined by different methods, from those of lower accuracy; so that even if such a regular distribution existed, it could not have been systematically the same on all the models. Therefore, the existence of leading-edge irregularities cannot explain the presence of a regular pattern of flow perturbations at reattachment. It is most probably a fundamental boundary-layer instability which in these tests is triggered by the leading-edge irregularities.

It is recognized that additional investigations remain to be done to determine exactly where the perturbations start to be regularly distributed. Without such information it is impossible to evaluate the flow curvature which is necessary to discuss the results in relation to Görtler's theory. Hopkins showed (Ref. 3) that the curvature existing at reattachment was two orders of magnitude greater than the minimum value required by Görtler and he concluded that the curvature required to produce vortices was so slight that this degree of curvature might even exists at the leading-edge. Therefore the large amplification of the intensity of the perturbations in the separated boundary-layer remains to be explained.

CONCLUSIONS

The flow perturbations extend, af ter reattachment, into the full thickness of the boundary-layer with a maximum intensity of pitot~pressure

variations occuring at about mid-height, both in the laminar and turbulent portions of the boundary-layer. These variations vanish at the outer-edge

of the boundary-layer and have their maximum amplitude in the transition region.

Although the existence of a regular pattern of flow perturbations

could not be explained by the presence of leading-edge irregularities, it

appears that the boundary-layer instability ,lias triggered by these

irregu-larities. No relation existed between the spacing (i.e. the wave-length)

of the flOH perturbations and the distribution of leading-edge

irregulari-ties, hO\lIever, the amplitude of the perturbations was approximately

pro-portional to the size of these irregularities. By extrapolation of the

results it is concluded that a two-dimensional boundary-1ayer f10\1I might

be obtained within one percent ( in

APp)

at reattachment, if the

leading-edge thickness were constant to within 1.'/2 to 1 micrön, ·assUmingno· other

effect such· as the influence of possib1e irregu1arities in the flow.

REFERENCES

1. J.J. Ginoux - Laminar separation in supersonic flow with emphasis on

three-dimensional perturbations at reattachment.

T.C.E.A. TN 3 - February 1960.

2. J.J. Ginoux - The T.C.E.A~ continuous supersonic wind tunnel S-l,

T.C.E.A. TM 7~October 1960.

3. E.J. Hopkins, S.J. Keating and A. Bandettini - Photographic evidence of

streatmllise arrays of vortices in boundary-layer flow,

NASA TN D-328 - September 1960.

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_{- -}

1rn;---~---r_---r_---~---~ 80 70 60 5 40 3

boundary -ley.r thickness vs. z

symbols zmm 1

₊

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38.5

boundary -Iayer profi les at various

z

and x: 81 mm

MODEL

s-

3

20~ ________ ~ ________ ~ ________ ~ ________ ~ ________ ~

o

ei) Model 5-3

b) Model 5-20-e

c) Model 5-20-e-B

cross-section (x,y)

NI

C"i

N

ui CD .... 11 11 )C )C 301 10

OL-.-.Jr....I.~ .~ ... ~.-..i-~~.,&,.- ~~ ... _ . ~1--A. --L :t...J_.1 ~_,r~del-!bis+/a-r.:t-.

-.,h'

T-'bo;; ._.

~ f,Pp'"

-F I G URE 6-a _ transverse variation of pitot- pressure at various x, in .,. ot the pitot-pressure on model-axis.

-40 FIGURE I/) I/) I 11 )( -80 -100 I/) o

....

I 11 ) (

cross-section (x.y) <]=:==-wind

-120 -140 -160

top - view (x,z)

y

x

model-axis

variation of pitot-pressure at various x, in Of. of the pitot-pressure on model- uis • measurements upstream ot the step (lC<O)

50

40

30

20

10, iI Y/' : 1.0

f

0

'~~~~~VI

.30 40 30 20

O~mJ"''''

\ Tmm

t

~

10

oL

~.,.

.

\11111

~1

1

6pp°,.

laading - edge

geometry MODEL 5-3

,1oo~1 ---L---+--~--~----~--~--~--4---~--~--~--~

m ~~

e

20

"""",,-_ "" "" lmllan thic

tn~

.Ar~r

o ~ . _ .... /IoNIN'

"ë ,.

-"

T 1""' ...

..--Zmm

., 1.. mod. I s20t

I

°

1

·L._

-+....

I ..}."f" ':In L.A P A -60 -70 Zmm FIGURE 8 _ _{Geometry of the leading - edge}

J

t

1 ppm ln

I

10 at1 0 4 0 Hg

I

2 0 __

IL

0 I

,....

1

r--I

I

T

+

X:-25mm

-•

x: "mm

-

--Ymm-o

th ickness-el.rr.nt I

1

10

-:p'"

f

201

~

I~

~

J-20

I

APp'" 10

I

0 I • ft .... A 11 \ ..

~-30

-10'

____ I\t

Y

III

\

~~ -50 -201- §44mm

I

-30L with thickness-element/ -40

~

I 10

'I.

z_g;;:~ind

Alp'"

~

t;içknns-ele~

I

0

~.~

.t the INding-edge J"'V ~-~~ ... of model s-6 f 10

fi%

I

0 -10 r----=-.,...-... without

t .

I"

-25 m > LWith th lekn .. s-.I .... nt

_

.Jll\...,

~

-10

~

.

"

,

,

)

f

/ou ~'Io 2n

I

0

I\.f'\r,.

1\ perturbat ion s

Iffl'l

2fa

JV

-""1 downstr.am

~*

5

thickness-eh~1 nent - of the step

on flow Den urbations 20 _...,~

x:"mm

,

40

MODEL 5-6

t

5

APp·" 0

n

1\. to ~

~

perturbat ion.

I

-5

...,.,.

_U~

r-J

\

_ ufstrtam

11

\

o the step -10 ~ x :-25mm -11:

.

t

40 reg!.9,n of incr~ased thickn.ss

~

.... À

microns 20 I.ad i ng - edge

I

...

.~ ... ~ r

-

...

- thickness 0 ~

....

! /

L ),

_/

_/

_/

_/

_/

_/

_/

_/

.

40

1

t

V /

/

/

/

/

/

/

/

/

_/

_{/ !}

microns 20

_l

_~ A. / "'-#V'~ .L

~

/

/

1

_lead ing-edge

I

-2~

.l!!

Ar

'-

~~

/.1

as seen from above its .~

upper surface'"';

;

~

"

-40 111 ~ S

"',

Ol 0 _EI E . "I -50 -45 I 415 5

-Zmm-F I G URE 10 _ Comparison between flow- perturbations and leading-edge g.om.try

t

~·I.

I

0

f

1

'0_% 6~0f0

I

liPt."

1

100/ •

I

1

100/ •

t

6pp'l.

I

0 Z m m

a) Model $-20-e-B c) Model $-20-c Figure 12. b) Model $-20-e d) Model $-20-f $ublimation technique

---.---~CEA TN 4

:TCEA TN 4

'Training Center for Experimental Aerodynamics

LEADING EDGE EFFECT ON SEPARATED

SUPERSONIC FLCMS

May 1961 Jean J. Ginoux Following earlier tests in the TCEA supersonic tunnel S-l, on a

two-dimen-sional baekward-facing step model in

Centre de Formation en Aérodynamique Expérimentale

I. GINOUX, Jean J.

~NFLUENCE

DU BORD D'ATTAQUE SUR LE

11. TCEA TN 4. OMPORTEMENT D'ECOULEMENTS SUPERSONIQUES

, DECOLLES

1. Flmv, eompress~- ai 1961 Jean J. Ginoux b1e (1.1.2) 2. Flm·" viscous (1.1.3) I. GINOUX, Jean J. H. TCEA TN 4. 1. Ecoulement, com-pressib1e (1.1.2) Flow, laminar (1.1.3.1) whieh span-wise perturbations ,vere foundl3.

in the reattaehment region, further

studies have been made using the same

4

.

Flow, turbulent

(1.1.3.2)

Une suite a été donnée à une étude expé-12. Ecou1ement,

vis-rimentale antérieure effectuée à la SOU~l queux (1.1.3)

flerie supersonique S-l du CFAE sur des 3. Eeoulement,

lami-~odèles bidimensionnels constitués par naire (1.1.3.1)

des décrochements de paroi en forme de

4.

Ecoulement, tur-and other simi1ar models. In these

later studies, the same three-dimension-al perturbations were detected into the full thiekness of the boundary-layer,

Cpv_erl

CEA TN 4

raining Center for Experimental

erodynamies

EADING EDGE EFFECT ON SEPARATED

UPERSONIC FLCMS

ay 1961 Jean J. Ginoux

~arche, au cours de 1aquel1e des pertur- bulent (1.1.3.2) bations tridimensionnelles avaient été

enregistrées dans la zone de recollement

de la eouche limite.

_(ypJ,r v_~_~Ql iTCEA TN 4

Centre de Formation en Aérodynamique Expérimentale

I. GINOUX, Jean J. IINFLUENCE DU BORD D'ATTAQUE SUR LE

I

I. GINOUX, Jean J.

11. TCEA TN 4. COMPORTEMENT D'ECOULEMENTS SUPERSONIQUES1II. TCEA TN 4.

1. Flow, compress~- '1961 J J G' 1. Ecou1ement,

com-ble (1.1.2) a~ ean • ~noux pressib1e (1.1.2)

~

' ollowing earlier tests in the TCEA

I

supersonie tunnel S-l, on a

t\vo-dimen-ional baekward-faeing step model in

,,,hieh span-\vise perturbations were found

, DECOLLES .

J

'

2. Flmv, viscous Une suite a été donnée à une étude expé- 2.

(1.1.3) rimentale antérieure effectuée à la so~

Ecoulement, vis-queux (1.1.3) 3. Flmv, laminar flerie supersonique S-l du CFAE sur des 3. Ecoulement,

lami-naire (1.1.3.1)

~

I

n the reattaehment region, further tudies have been made using the same

nd other similar models. In these ater studies, the same

three-dimension-1 perturbations 'vere deteeted into the

ull thiekness of the boundary-layer,

(1.1.3.1) modHes bidimensionnels constitués par 4. Flow, turbulent des décrochements de paroi en forme de

(1.1.3.2) arche, au cours de laquelle des pertur-bations tridimensionnelles avaient été enregistrées and la zone de recollement

de la couche limite.

__________________________ ~(o~v~e=r~)~ __ ~_______ (voir verso)

4. Ecoulement, tur-bulent (1.1.3.2)

of the flo"l. Their amplitude ''Jas a maximum in the transi-tion region.

daient dans toute l'épaisseur de la couche limite, tant dans la région laminaire de l'écoulement que dans sa partie tur-bulente, avec une amplitude maximum dans la zone de transiticn

In using a model \..:rith a much improved accuracy of

manufac-L'amélioration de la précision d'usinage du bord d'attaque ture, notably at the leading-edge, it was found that the

a permis de diminuer l' amplitude des perturbations (cette amplitude of the perturbations \'laS greatly reduced, roughly

dernière étant approximativement proportionnelle à la dimen- in proportion to the size of the irregularities of manufac-sion des irrégularités du bord d'attaque) et cela sans que ture of the leading-edge itself. As it is unreasonable to la longueur d'onde des perturbations ne soit modifiée. Etant expect these to be anything other than random in character,

donné qu'il est raisonnable de considérer ces irrégularités it is concluded that the phenomenon is essentially one of

comme réparties de manière aléatoire, il a été conclu que le instability in the two-dimensional flow, the main triggerin~

phénomène considéré représentait essentiellement une insta- action arising, at least in the earlier tests, from small bilité de l'écoulement bidimensionnel, dont le déclenchement irregularities in the leading-edge.

était provoqué par des irrégu1arités extrêmement petites

dans le bord d'attaque.

,Copies disponiblesau CFAE, Rhode-St-Genèse, Belgique. Copies available at TCEA, Rhode-St-Genèse, Belgium.

On a montré qu'après recollement, ces perturbations s'éten- af ter reattachrnent, both in turbulent and laminar regions daient dans toute 11 _{épaisseur de la couche limite, tant dans of the flow. Their amplitude >..:ras a maximum in the}

transi-la région transi-laminaire de l'écou1ement que dans Sa partie tur- tion region. bulente, avec une amplitude mmdmum dans la zone de transition.

In using a model with a much improved accuracy of manufac-L'amélioration de la précision d'usinage du bord d'attaque ture, notably at the leading-edge, it was found that the

a permis de diminuer l'amplitude des perturbations (cette amplitude of the perturbations was greatly reduced, roughly

dernière étant approximativement proportionnelle à la dimen- in proportion to the size of the irregularities of manufac-sion des irrégularités du bord d'attaque) et cela sans que ture of the leading-edge itself. As it is unreasonable to

la longueur d'onde des perturbations ne soit modifiée. Etant expect these to be anything other than random in character,

donné qu'il est raisonnable de considérer ces irrégularités it is concluded that the phenomenon is essentially one of

comme réparties de manière aléatoire, il a été conclu que le instability in the t,."o-dimensional flo,.", the main triggering,

phénomène considéré représentait essentiellement une insta- action arising, at least in the earlier tests, from small bilité de l'écoulement bidimensionnel, dont Ie déclenchement irregularities in the leading-edge.

était provoqué par des irrégu1arités extrêmement petites

dans le bord d'attaque.

I

;TCEA TN 4

'Training Center for Experimental

Aerodynamics

LEADING EDGE EFFECT ON SEPARATED SUPERSONIC FLGJS

May 1961 Jean J. Ginoux

IIFOllOWing earlier tests in the TCEA

supersonic tunnel S-l, on a two-dimen-sional backward-facing step model in

:which span-wise perturbations were found

in the reattachment region, further studies have been made using the same and other similar models. In these

later studies, the same three-dimension-al perturbations were detected into the

fu11 thickness of the boundary-layer,

{ovJ~rJ

CEA TN 4

raining Center for Experimental erodynamics

EADING EDGE EFFECT ON SEPARATED UPERSONIC FLGJS

ay 1961 Jean J. Ginoux

Following earlier tests in the TCEA

supersonic tunnel S-l, on a t,vo-d~men­

~ional backward-facing step model in

'TCEA TN 4

Centre de Formation en Aérodynamique

Expérimentale

I

I

11. TCEA TN 4. OMPORTEMENT D'ECOULEMENTS SUPERSONIQUES •

GINOUX, Jean Jo-TCEA TN 4.

I. GINOUX, Jean

J.~NFLUENCE

DU BORD D'ATTAQUE SUR LE 11·

, DECOLLES

1. Flow, compress~- ai 1961

b1e (1.1.2) Jean J. Ginoux

1. Ecoulement, com-pressible (1.1.2) 2. Flow, viscous (1.1.3) 3. Flow, 1aminar (1.1.3.1)

4

.

Flow, turbulent (1.1.3.2) I. GINOUX, Jean J. Il. TCEA TN 4.

Une suite a été donnée à une étude expé-12. Ecoulement,

vis-rimentale antérieure effectuée à la SOU] queux (1.1.3) f1erie supersonique S-l du CFAE sur des 3. Ecou1ement,

1ami-~odè1es bidimensionne1s constitués par naire (1.1.3.1)

des décrochements de paroi en forme de

4.

Ecou1ement,

tur-~arche, au cours de laquelle des pertur- bulent (1.1.3.2)

bations tridimensionnelles avaient été enregistrées dans la zone de recollement de la couche 1imite.

(voix_YersQ)

~CEA TN 4

Centre de Formation en Aérodynamique

Expérimentale

INFLUENCE DU BORD D'ATTAQUE SUR LE

COMPORTEMENT D'ECOULEMENTS SUPERSONIQUES

I. GINOUX, Jean J. Il. TCEA TN 4.

1. Flow, compressi_l~ECOLLES

bIe (1.1.2) IMai 1961 Jean J. Ginoux

1. Ecou1ement, com-pressib1e (1.1.2) 2. Flow, viscous

(1.l.3)

,..,hich span-wise perturbations were foundl3.

'n the reattachment region, further

F 10.01, laminar

(1.1.3.1)

Une suite a été donnée à une étude expé- 2. Ecou1ement,

vis-rimenta1e antérieure effectuée à la souf- queux (1.l.3) f1erie supersonique S-l du CFAE sur des 3. Ecou1ement, 1ami-modèles bidimensionnels constitués par naire (1.1.3.1) des décrochements de paroi en forme de

4.

Ecoulement, tur-tudies have been made using the same

nd other similar modeis. In these ater studies, the same

three-dimension-1 perturbations ,vere detected into the

uIl thickness of the boundary-layer, (over)

4.

Flow, turbulent

(1.1.3.2) Farche, au cours de laquelle des pertur- bulent (1.1.3.2) bations tridimensionnelles avaient été

enregistrées and' la zone de recollement de la couche limite.

of the flO'·I. Their amplitude \\las a maximum in the transi-tion region.

daient dans toute l'épaisseur de la couche limite, tant dans la région laminaire de l'écou1ement que dans sa partie tur-bulente, avec une amplitude maximum dans la zone de transitiCX\

In using a model \vith a much improved accuracy of manufac-L'amé1ioration de la précision d'usinage du bord d'attaque ture, notab1y at the 1eading-edge, it was found that the

a permis de diminuer l'amplitude des perturbations (cette amplitude of the perturbations was greatly reduced, roughly

dernière étant approximativement proportionnelle à la dimen- in proportion to the size of the irregularities of manufac

-sion des irrégularités du bord d'attaque) et cela sans que ture of. the leading-edge itself. As it is unreasonable to la longueur d'onde des perturbations ne soit modifiée. Etant expect these to be anything other than random in character,

donné qu'il est raisonnable de considérer ces irrégularités it is concluded that the phenomenon is essentially one of

comme réparties de manière aléatdire, il a été conc1u que le instability in the two-dimensional flow, the main triggerinÉ

phénomène considéré représentait essentiellement une insta- action arising, at least in the earlier tests, from smal1

bi1ité de l'écoulement bidimensionnel, dont le déclenchement irregu1arities in the leading-edge.

était provoqué par des irrégularités extrêmement petites

dans le bord d'attaque.

,Copies disponib1esau ~FAE, Rhode-St-Genèse, Be1gique. !Copies avai1ab1e at TCEA, Rhode-St-Genèse, Be1gium.

On a montré qu'après recol1ement, ces perturbations

s'éten-daient dans toute l'épaisseur de la couche limite, tant dans la région laminaire de l'écoulement que dans sa partie

tur-af ter reattachment, both in turbulent and 1aminar regions of the f10\v. Their amplitude \.Jas a maximwn in the transi-tion region.

bulente, avec une amplitude maximum dans la zone de transition. I ' _{n us~ng a mo e} d l ' h h ' _{w~t a mue ~mprove} d _{accuracy 0} f _{manu ac-}f

L'amélioration de la précision d'usinage du bord d'attaque ture, notably at the 1eading-edge, it was found that the

a permis de diminuer l'amplitude des perturbations (eette amplitude of the perturbations was great1y reduced, roughly

dernière étant approximativement proportionnelle à la dimen- in proportion to the size of the irregularities of

manufac-sion des irrégularités du bord d'attaque) et ce1a sans que ture of the leading-edge itself. As it is unreasonable to

la longueur d'onde des perturbations ne soit modifiée. Etant expeet these to be anything other than random in character,

donné qu'il est raisonnable de considérer ces irrégularités it is coneluded that the phenomenon is essentially one of comme réparties de manière aléatoire, il a été eonclu que le instability in the t\vo-dimensional flml1, the main triggering

phénomène considéré représentait essentiellement une insta- action arising, at least in the earlier tests, from small

bilité de l'écoulement bidimensionnel, dont le déclenchement irregularities in the leading-edge.

était provoqué par des irrégularités extrêmement petites

dans le bord d'attaque.

I