An experimental Adaptive Wall Test Section (AWTS) process is described. Comparisons of the ONERA T2 and the 0.3-m TCT (transonic cryogenic tunnel) AWTS data for the ONERA CAST-10 airfoil are presented. Most of the 0.3-m TCT data is new and preliminary and no sidewall boundary layer control is involved. No conclusions are given

Jenkins, Renaldo

Wolf, Stephen

English

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N90=17653
AN EXPERIMENTAL AWTS PROCESS
AND
COMPARISONS OF ONERA "I"2AND 0.3-M TCT AWTS DATA
FOR THE ONERA CAST=I0 AEROFOIL
Stephen Wolf
Vigyan Research Assochtes
and
Renaldo Jenkins
NASA Langley Research Center
PRECEDING PAGE BLANK NOT FILMED 137
https://ntrs.nasa.gov/search.jsp?R=19900008337 2020-03-19T23:56:42+00:00Z
ORIGINAL PAGE
BLACK AND WHITE PHOTOGRAPH
NASA Langley 0.3-m TCT
Flexible walled AWTS
installed in the 0.3-m TCT
AcUuaUors
Sketch of flexible walled AWTS showing
jack actuators above and below the pressure shell
13B
EXPERIMENTAL AWTS PROCESS
IN THE 0.3-m TCT
Test Section Design - Four solid walls, floor and ceiling adjustable.
Total of 21 wall jacks per wall (note only 18 wall
jacks used in wall adjustment process).
Wall Adjustment Process - Fast and iterative, based on wall data only.
Judd method with linearised compressible flow theory
(2-D testing only).
Wall Data - Ceiling and floor jack positions.
Ceiling and floor pressures on the tunnel centerline.
We began operating the NASA Langley 0.3-m TCT (Transonic Cryogenic Tunnel) with an
Adaptive Wall Test Section (AWTS) in March 1986.1 The AWTS has a 33 cm (13 inch) square
cross-section with four solid walls. The floor and ceiling are adjustable. We control the wall
shapes with a system of 21 computer controlled jacks. We use only 18 jacks per wall in the wall
adjustment process. The 3 downstream jacks simply control a variable diffuser to provide a
smooth interface between the AWTS and the rigid tunnel circuit.
The wall adjustment process is both fast and iterative and requires only information on the
flexible walls. The theory of the process utilizes the well-proven Judd method using linear_zed
theory. _
We obtain the wall data for the wall adjustment process and residual interference assessment
simply by measuring the jack positions and the wall pressures on the tunnel centerline.
139
QUALITY OF WALL ADJUSTMENTS / STREAMLINING
Assessment of Residual Wall Interferences
Input data - Measured and calculated wall pressures.
Aerodynamic position of floor and ceiling.
Position of model chordline in the AWTS.
Empirical Maxima -
1) Average Cp error (between streamline and measured values)
along each wall - 0.01
2) Induced angle of attack at the model leading edge - 0.015 °
3) Induced camber along the model chordline - 0.07 °
4) Average induced streamwise Cp error along the model
chordline - 0.007
We assess the quality of the wall adjustments/streamlining by calculating the residual wall
interferences due to the floor and ceiling. The calculations are quick (allowing real-time use)
using linearized compressible flow theory with the input data listed above.
The wall adjustment process automatically stops when all the residual wall interferences reduce
below the maxima listed above. These maxima are defined empirically as a compromise between
perfection (zero residual wall interferences) and unnecessary iterations of the wall adjustment
process. These maxima are related to the quality of the AWTS hardware and instrumentation and
stability of test conditions in the AWTS.
We do not apply any of these residual wall interference corrections to the final aerofoil data. We
consider the real-time aerofoil data to be "corrected." In this adaptive wall context, "corrected"
refers to the elimination of wall interferences at the source of these interferences.
140
COMPARISONS OF T2 AND 0.3-m TCT AEROFOIL DATA
Comparison Qualifications
Most of 0.3-m TCT data is new and preliminary.
Concentration on data at the design Mach number.
No sidewall boundary layer control involved.
Similar testing techniques in T2 and 0.3-m TCT.
No conclusions given to bias the workshop discussions.
Before we present any data comparisons, it should be known that the above qualifications apply
to the comparisons. Most of the 0.3-m TCT data presented here is new and unpublished and
must therefore be considered as preliminary. This new data comes from a re-test (T-224) of the
ONERA CAST l0 carried out in August 1988. (Original 0.3-m TCT data came from tests T-212
and T-216.) We found it necessary to carry out this re-test due to discrepancies in the 0.3-m
TCT data from the two CAST 10 models. We will not discuss these discrepancies here.
We concentrate the data comparisons on the design Math number 0.765 because of theknown
sensitivity of the CAST 10 section at this Mach number. This sensitive situation acts as an
excellent challenge for free air simulations.
We did not use sidewall boundary layer control during the 0.3-m TCT tests nor did the French in
their tests.
The ONERA/CERT T2 tunnel and the 0.3-m TCT use similar testing techniques. Both tunnels
have flexible walled AWTS's. We do not discuss the French wall adjustment process here. Suffice
to say, the process is well established at ONERA and is similar to the NASA process. However
the T2 wall adjustment process does not involve any residual wall interference assessment due to
the intermittent tunnel operation. Interestingly, we did attempt to use the T2 wall adjustment
process with the 0.3-m TCT but failed to achieve a converged solution due mainly to software
problems.
We do not give any conclusions in this presentation to bias any discussion of these data
comparisons. We present these data comparisons with comments as input for the forthcoming
workshop discussions.
141
TESTING FACTS
OAerofoil Chord - 18 cm (7.09 inches)
OTest Section Height/Chord Ratio - 1.83 (0.3-m TCT) & 2.05 (T2)
OAspect Ratio - 1.833 (0.3-m TCT) & 2.166 (T2)
OTransition Location on both surfaces - 6% (0.3-m TCT) & 5% (T2)
OTransition Strip - 1.7% of 0.053/0.043mm dia. micro-spheres (0.3-m TCT)
0.045ram high carborundum grit (T2)
OMach Number Stability - 0.002 (0.3-m TCT) & 0.004 (T2)
OData Shortfall - Sparsity of high Reynolds number data from T2
The testing facts listed above define the model condition for the data compared here. The
transition strip location in the NASA tests is a compromise between the ONERA and DFVLR
locations.
Mach number stability during a polar is a problem in the T2 tunnel because each data point is a
separate run of this intermittent tunnel. The 0.3-m TCT is a continuously operating tunnel.
The T2 data we used here is not complete.
example. This incompleteness makes it
comparisons than shown here.
There is a sparsity of high Reynolds number data for
very difficult to make more meaningful direct
142
t-
O
t"
.v_ .8
O
ta-
Q)
O
(.3 .6
¢D
t3
k.
O
I.t.
.4
O
E
k.
O
Z'.2
ONERA CAST 10 Aerofoil Data
Math = 0.765 ; Re = 21 million ; Transition Free
1.2
--B-- TCT T-224
x T2 Data
i X
!
!
!
!
X !
I
I
I
0 , ! , , , ,
-3 -'2 -1 O 1 2 3 4 5
Angle of Attack, degrees
This data comparison is for the test conditions Mach 0.765, 21 million chord Reynolds number,
and transition free. The Cn-v-cz data shown above indicates an a difference between the two
tunnels. It seems as though Cn is matched but the sparsity of T2 data does add some
uncertainty. The range of Mach 'n'_"mberin the four T2 data points is 0.007, compared with
0.0003 in the 0.3-m TCT data.
143
ONERA CAST 10 Aerofoil Data
Mach = 0.765 ; Rc = 21 million ; Transition Free
.05
"10
0
c
,u
o
o
0
at
o
I,,.
r'_
.04
.O3
.O2
.01
--s- TCT T-224
x T2 Doto
x _ x
/
' I i I I I
0 .2 .4 .6 .e 1 1.2
Normal Force Coefficient, Cn
Continuing the data comparison at 21 million chord Reynolds number. The graph of Cd-v-Cn
shows a remarkably good data comparison. This confirms that there is an a difference between
the two tunnels. The repeatability of data on a known sensitive aerofoil is always a challenge.
Add to this challenge, tests in different tunnels with natural transition and you have the very
demanding situation discussed here.
144
ONERA CAST 10 Aerofoil Data
Mach = 0.765 ; Rc = 4 million ; Transition Fixed
1.2
C
0
r"
.'__.
o
,w
N,-
Q3
0
(.3
¢0(J
L
o
LL
0
E
k.
0
Z
.S
.6
.4
.2
--B- TCT T-224
x T2 DQtn
v TCT T-212
v __ v v
/ !
!
/
x/ !
0 . , I , . , ,
-3 -2 -1 o , 2 3 _ s
Angle of Attack, degrees
I£ we now reduce the chord Reynolds number in the data comparison to 4 m/Ilion, we find much
more 1"2 data. The Cn-v-a data again indicates that there is an a difference persisting between
the two tunnels. We have more confidence in the matching of Cn _x at this lower Reynolds
• jln .
number. We include the original 0.3-m TCT data set (T-212) m thzs comparison to show data
repeatability. Notice the latest set (T-224) has slightly higher Cn values• Nevertheless, both sets
of 0.3-m TCT data show a higher lift curve slope than found in T2.
145
ONERA CAST
Mach = 0.765 ; Rc =
.05
10 Aerofoil Data
4 million ; Transition Fixed
_O
(3
t-
(J
te-
0
(.3
O_
0
.04 ¸
.03 '
.O2
.01
0
--8- TCT T-224
x T2 Data
v TCT T-212
V
v
x x x
; " "'= I ! • !
0 .2 .4 .6 .8 1 1.2
Normol Force Coefficient. Cn
When we remove e from the 4 million Reynolds number data, we see another source of data
differences. In the Cd-v-Cn graph shown above, we see that the two 0.3-m TCT data sets
bracket the T2 data in terms of Cd . and Cn . It is clear that the transition fixing is
significantly affecting lift and drag. _his highl_ts one of the major problems of simulating
scale effects. The what, where and how much of transition fixing remains a big question.
Another factor we must consider is the improved tunnel control system for the latest 0.3-m TCT
test (T-224). We have more confidence in the drag from the latest tests.
146
ONERA CAST 10 Aerofoil Data
Moch = 0.765 ; Rc = 4 million ; Alpha = I degree
1.5 ] Transition Fixed
u
O
-J .5
0
---Q-- TCT T-212 .570
--e--- T2 Data .542
---B-- GRUMFOIL
| i i i
0 .2 .4 .6 .8
Stotion. x/c
The comparison of detailed pressure distributions on the aerofoil are difficult. This is because
the normal force was not matched between the two tunnels at ]iftlng conditions. However, it is
interesting to make a data comparison at ¢ = 1° and Mach 0.765, with transition fixed, as shown
above. This is a challenging test condition with near maximum lift. The comparison is good with
notable differences near the leading edge (due to the transition strip) and at the shock location.
The movement ofthe shock is small, of the order of the pressure tap spacing (2.5% of chord).
We also include a GRUMFOIL free air solution in this comparison. The normal force of the
GRUMFOIL result is matched to that of the 0.3-m TCT data. The comparison is very good.
Incidentally, other comparisons with GRUMFOIL have been made which are also good provided
Cn is less than Cnm,,x and the transition location on the aerofoil is known.
147
ONERA
Mach = 0.7
1.2
CAST 10 Aerofoil Data
; Rc = 5.7 million ; Transition Fixed
c
rJ
c
u
o
0
u
o
i,
o
E
I,..
o
Z
1
.8
.6
.4
' .2
--m- TCT T-224
x T2 Data
x/x
/ I
I/
X i
,/
0 , , I ....
-3 -2 -1 0 1 2 3 4. 5
Angle of Attack, degrees
So far we have compared data at only the design Mach number. If we examine data at Mach 0.7
we see a similar trend in the Cn-v-<l graph shown above. Again there is the same _ difference
between the two tunnels as seen at higher Mach number and Reynolds number. Unfortunately,
we believe that Cnma x could not be obtained in the T2 tunnel at Mach 0.7, due to limitations to
the flexible wall movement in the T2 AWLS. The 3.7 million chord Reynolds number of this
data coincides with the majority of T2 tests at Mach 0.7.
Unfortunately, very little T2 data exists above Mach 0.765, so no data comparisons are possible
for Mach numbers higher than the design value.
148
.05"
ONERA CAST 10 Aerofoil Dafa
Math = 0.7 ; Rc = 3.7 million ; Transition Fixed
.o4
8
._ .03
.5
0 .02
.01
0
-19-- TCT T-224 ._
T T I" 1" T
0 .2 .4 .6 .8 1 1.2
Normol Force Coefficient, Cn
The Cd-v-Cn data at Mach 0.7 and 3.7 million chord Reynolds number shows a similar
comparison as found at Math 0.765. Once again the 0.3-m TCT data has lower drag than the T2
data by about 20 drag counts. This drag difference is due to the state of the transition fixing.
The French grit is thicker than the NASA Micro-Spheres in this case.
i49
ONERA CAST 10 Aerofoil Data
Alpha = I degree; Rc = 20 million
.8
c .7
Q;
CO
L_.
0.4
Z
TCTI- Transition Fixed
o T2 ;
.3 ! I !
.7 .72 .74 .76
Freestreom Moch no.
!
.78 .8
Let us now examine the effect of Mach number at a fixed _. We choose to look at data at 20
million chordReynoldsnumber where we expect the effects of transition fixing to be minimal. A
plot of Cn-v-Mach number is shown above over the Mach number range 0.7 to 0.8. Notice the
shock stall in the 0.3-m TCT data (from T-216) occurs at about Mach 0.74 transition fixed and
about Mach 0.75 transition free. There is insufficient I"2 data to see shock stall, but what we can
see is a minimal effect of transition fixing. This indicates that the T2 transition fixing was well
scaled for 20 million chord Reynolds number.
At the design Mach number, the 0.3-m TCT data indicates that Cn ;is very sensitive to transition
fixing and Mach number at this high lift condition.
150
.05
ONERA CAST 10 Aerofoil Data
Alpha = 1 degree; Rc = 20 million
.O4
.03
0 .02
.01
0
--B-
TCT}j Transition Free
x T2 ;
_l'
TCT | _.
T2 t Transition Fixed, fjl
I I I I
.7 .72 .74 .76 .78 .8
Freestream Much no.
We now look at how the drag coefficient, Cd, varies with Math number for the same
conditions as shown in the previous figure. We see that the effect of transition on the 0.3-m
TCT data is as small as found in the limited T2 data. The 0.3-m TCT data are faired to remove
some clearly wayward data points. We attribute this scatter to the less than perfect tunnel control
system used in the initial 0.3-m TCT tests (T-216).
We see that the T2 drag at Mach 0.765 is significantly lower than the 0.3-m TCT value. This
seems to indicate that the effective a of the T2 data is lower than the geometrical a.
151
.8
ONERA CAST 10 Aerofoil Data
Alpho = I degree; Moch = 0.765
t--
0.7
r-
t3
,m
te-
_.- .6
0
C)
_J
0.5 ¸
LL
o
E
L
0.4
Z
0
TCTi
x T2 •__ansition Fixed
TCT_Transition Free
o T2 )
.3
! • l i |
0 5 10 15 20 25 30
Chord Reynolds Number. Rc
We consider Reynolds number effects at the same a of 1° using 0.3-m TCT data from the initial
test (T-212). The plot of Cn-v-Rc shown above is for the chord Reynolds number range from 4
million to 21.2 million with transition fixed. We can observe that the effect of transition fixing
as Reynolds number increases is not straightforward. Meanwhile, data comparisons at a lower
of 0.25 ° show that the effect of transition fixing reduces as Reynolds number increases, as
expected.
However, we can see that the transition free data from the 0.3-m TCT shows a small Reynolds
number effect concentrated between 4 and 6 million. With transition fixed, the Reynolds number
effects are larger and occur over the entire Reynolds number range investigated.
The limited T2 data shows that there is minimal transition effect at 21 million chord Reynolds
number, again pointing to good sizing of the transition grit for high Reynolds number testing.
The Reynolds number effects are small compared with Mach number effects. However, we can
see that incorrect transition fixing can have serious consequences.
152
SUMMARY OF FINDINGS
Remarkable data agreement with the limited high Reynolds data from T2.
Angle of attack difference between the two tunnels.
Drag differences at low Reynolds number.
Good agreement with free air GRUMFOIL code, below Cnma x.
More T2 data required to confirm some observations.
References
1. Wolf, S. W. D.; and Ray, E. J.: Highlights of Experience with a Flexible Walled Test Section
in the NASA Langley 0.3-Meter Transonic Cryogenic Tunnel. AIAA Paper 88-2036. Presented
at the AIAA 15th Aerodynamic Testing Conference, San Diego, CA, May 18-20, 1988.
2. Wolf, S. W. D., and Goodyer, M. J.: Predictive Wall Adjustment Strategy for Two-
Dimensional Flexible Walled Adaptive Wind Tunnel. A Detailed Description of the First One-
Step Method. NASA CR-181635, January 1988, N88-19409#.
153



An experimental AWTS process and comparisons of ONERA T2 and 0.3-m TCT AWTS data for the ONERA CAST-10 aerofoil

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