Activities report include (1) completion of measurements of turbulence amplification in flow about a circular cylinder; (2) initiation of the measurements of turbulence characteristics in flow about a single symmetric airfoil; and, (3) further examination of various matching numerical methods. Emphasis is placed on the experimental program conducted to obtain data on the amplification of the oncoming turbulence and its management

Sadeh, W. Z.

English

NASA Technical Reports Server

General Disclaimer 
One or more of the Following Statements may affect this Document 
 
 This document has been reproduced from the best copy furnished by the 
organizational source. It is being released in the interest of making available as 
much information as possible. 
 
 This document may contain data, which exceeds the sheet parameters. It was 
furnished in this condition by the organizational source and is the best copy 
available. 
 
 This document may contain tone-on-tone or color graphs, charts and/or pictures, 
which have been reproduced in black and white. 
 
 This document is paginated as submitted by the original source. 
 
 Portions of this document are not fully legible due to the historical nature of some 
of the material. However, it is the best reproduction available from the original 
submission. 
 
 
 
 
 
 
 
Produced by the NASA Center for Aerospace Information (CASI) 
https://ntrs.nasa.gov/search.jsp?R=19790013865 2020-03-22T00:12:58+00:00Z
EFFECTS OF TURBULENCE ON LAMINAR SEPARATION
ON AERODYNAMIC SURFACES SUCH AS
AIRFOILS AND COMPRESSOR BLADING
-Willy Z. Sadeh, Professor of Engineering
Principal Investigator
(NASA—CR-158488) EFFECTS OF TURBULENCE ON
1AMINAR SEPARATION ON AERODYNAMIC SURFACES
SUCH AS AIRFOILS AND COMPRESSOR BLADING
Seoiannual Status Report, 1 Oct. 1978 - 31
Mar. 1979 (Colorado State Univ.) 8 p
N79-22036
Unclas
G3/02 24710
Semi-Annual Status Report
1 October 1978 to 31 March 1979
for
Lewis Research Center
National Aeronautics and Space Administration
11734.e
9 CAN-\;
Fluid Mechanics and Wind Engineering Program 	 p^ut^GL1 
Department of Civil Engineering
Colorado State University
Fort Collins, Colorado 80523
April 1979
Research Grant NSG 3127
(CSU Ref. No. 31-1372-1935)
I .	 Scientific Significance
The long-term goal of this research program is the determination of the
effects of oncoming turbulence on laminar separation on aerodynamic surfaces
such as airfoils and axial-compressor blading. In flow through a blade cascade
at a Reynolds number of 240 5
 or smaller the development of laminar separation
on the airfoil .suction side leads to prohibitively high aerodynamic losses. The
growth of the laminar separation bubble can even yield fully stalled blades.
Significant reduction of the aerodynamic losses including prevention of laminar
separation is achievable by inducing the development of a profile turbulent
boundary layer. Such a turbulent boundary-layer can be generated through supply-
ing oncoming turbulent energy concentrated at scales commensurate with the thick-
ness of the prevailing laminar boundary layer. The mechanism through which
adequate accumulation of turbulent energy can be produced and suppiied at the
desired scales lies in the turbulence amplification characteristic of forward
stagnation flow. This selective amplification is governed by the vortex
stretching mechanism.
The research program is divided into three phases of increasing complexity.
In each phase the evolution of the oncoming turbulent energy, its selective am-
plification, its management, and ultimately, its effects on the body boundary
layer are to be investigated. During the first phase of this program the turbu-
lence amplification in flow about a circular cylinder and the effects of the am-
plified turbulent energy upon the cylinder boundary layer are being investigated.
The knowledge gained from this diagnostic study is to be utilized to identify
the vari is phenomena of interest and their application for conducting effi-
ciently t e research tasks of the other two phases. In the second and third
phases single airfoils and a blade cascade, respectively, are to be employed.
The theoretical work focused on the furtherance of the vorticity-amplifica-
tion theory for determining how the amplified turbulence is to be supplied to
the boundary layer for retarding and even forestalling laminar separation. To
this end, the matching of the outer and inner solutions of the vorticity-ampli-
fication theory is to be attempted. Matched asymptotic expansions are to be
carried out to meet this objective.
2.	 Current status
The research efforts during the subject period concentrated on: (1) com-
pletion of the measurements of turbulence amplification in flow about a circular
cylinder; (2) initiation of the measurements of turbulence characteristics in
flow about a single symmetric airfoil; and, (3) further examination of various
matching numerical methods. Emphasis was placed, however, on the experimental
program in order to obtain data on the amplification of the oncoming turbulence
and its management.
2.1 Flow about a circular cylinder
A paper describing the results of the visualization study of turbulence in
flow about a circular cylinder was submitted to and found suitable for publica-
tion in the Journal of Fluid Mechanics. A revised manuscript of this paper
titled "A Visual Investigation of Turbulence in Stagnation Flow About a Circular
Cylinder" was sent to the editor on 6 March 1979. A second short paper summariz-
ing some of the main aspects of the visualization study was accepted for presen-
tation at and publication in the Proceedings of the ASME Symposium on Aerodynamics
of Transportation to be held in Niagara Falls, NY from 18-20 June 1979. The
title of this paper is "Visualization of Turbulence in Flow About a Bluff Body"
and it is scheduled for presentation in the session on Bluff Body Aerodynamics.
The technical report on the effect of amplified turbulence upon the separa-
tion on a circular cylinder is in its completion stage. A summary of the
results of this investigation was outlined -in the last semi-annual status report.
It is anticipated that this technical report will be submitted for publication
as a NASA CR within four to six weeks. At the present time, a paper based on
this forthcoming technical report was accepted for presentation at and publication
as a preprint of the -AIAA 12th Fluid and Plasma Dynamics Conference to be held in
Williamsburg, Virginia from 23-25 July 1979. The title of this paper is "Free-
stream Turbulence Effect on Laminar Separation on a Circular Cylinder."
The reduction and analysis of the data collected at the planned six sub-
critical Reynolds numbers (5x104
 to 2x10 5 ) is still in progress. Computer
codes for conducting this analysis were completed and tested. The results clearly
point out the occurrence of selective amplification at scales larger than the
neutral one and the existence of a most amplified scale. Amplification ratios
up to about 10 were measured at particular scales. The results indicate further
that the turbulence amplification can be managed depending upon the combination
of the Reynolds number and the upwind grid position. Two technical reports con-
centrating on the experimental results and the methods of data reduction are
being prepared. Furthermore, the experimental results will be incorporated in
the forthcoming Ph.D. dissertation of Mr. H. J. Brauer.
2.2 Flow about a single airfoil
A preliminary survey of the freestream turbulence evolution in flow about
a symmetric NACA 65-010 airfoil with a chord c and a span s of 122 cm (48
in) and 183 cm (6 ft), respectively, was conducted along the stagnation stream-
line. These measurements were carried out at a zero angle of attack with the
turbulence -generating grid installed at an upwind distance of a half chord, i.e.,
X 2 = 0.5c	 (x2g = 61 cm (24 in)). Amplification of the streamwise turbulent
energy-i.e. the mean-square value of the streamwise component of the turbulent
velocity u^-beyond 60% was measured. A sample of the variation of the stream-
wise turbulent energy with approaching distance to the airfoil leading edge at a
profile-chord Reynolds number of 10 5
 (freestream velocity U2,, = 1.22 m/s (4 ft/s)
and air kinematic viscosity at 20°C (68°F) v = 1.5x10 -5
 m/s 2 ( 1.6x10 -4 ft/s2))
is displayed in Fig. 1. This streamwise turbulent energy is made dimensionless
with respect to its value at x2 = 7.62 em (3 in; x 2 = 0.0625) where a minimum
turbulence intensity of about 8 % (based on the freestream velocity U 211) was
monitored. The thickness of the turbulent stagnation boundary layer was esti-
mated based on thevariation of the streamwise mean velocity (U 2 ), fluctuating
velocity	 and turbulent energy (u). A thickness of about 3.05 mm (0.12
in; d = 0.0025) was found and it is demarcated by a dashed line in Fig. 1. It
is interesting to point out that this thickness is, as expected, about twice that
of the theoretical stagnation laminar boundary layer based on the results for
3the flat plate stagnation flow. Within the boundary layer, the turbulent energy
(and the fluctuating velocity) decays as shown in the inset incorporated in
Fig. 1.
A sample of the variation of the discrete turbulent energy at four selected
scales is shown in Fig. 2. The discrete energy at each scale a is made dimen-
sionless with respect to its value at x2 = 45.75 cm (18 in; R2 = 0.375) upstream
of the airfoil. This station is 15.24 cm (6 in) downstream of the turbulence-
generating grid. Amplification of discrete turbulent energy up to about 4.5
times the reference upstream level was obtained at A = 10 and 20 mm (0.39 and
0.79 in; ^ = 0.0082 and 0.0164). Most of the amplification occurred within an
upwind range of 0.01 of the profile chord (R2 up 0.01). This is roughly the
linear deceleration velocity range of the stagnation flow. It is further impor-
tant to point out the occurrence of one or more most amplified scales that are
not necessarily the largest ones. For instance, more amplification of turbulent
energy was measured at scales of 10 and-20 mm than at a scale of 40 mm (1.57 in;
a = 0.0327) as clearly shown in Fig. 2. These preliminary results attest to the
selective amplification of turbulent energy at preferred scales according to the
vorticity-amplification theory. It is apparent, furthermore, that one can govern
the concentration of turbulent energy at selected scales by controlling the grid
position and characteristics at a given Reynolds number. This management of the
selective turbulence amplification is presently being investigated.
The concentration of turbulent energy at particular scales is governed by
the stretching and tilting of the cross-vortex tubes according to the vorticity-
amplification theory. As a result, a coherent substructure consisting of a regu-
lar array of standing cross-vortex tubes emerges near the body stagnation zone.
This coherent substructure was visualized in both the flow about a circular cylin-
der (see NASA CR 3019, October 1978) and about a single symmetric NACA 65-010
airfoil (see Semi-Annual Status Report, 1 October 1977 to 31 March 1978). As a
matter of fact, a technical report including a short movie concerning the visual-
ization of this coherent substructure in flow about a symmetric airfoil is planned.
It should be stressed that in flow about an airfoil the stretching of cross-
vortex tubes is primarily dominated by their tilting around the profile. The
flow divergence around a streamline body at a zero angle of attack occurs over a
much smaller spatial scale and much more swiftly than in flow about a bluff body.
This is due to the difference in the bluffness of the body. Pure stretching is,
therefore, of lesser significance in flow about an airfoil than around a circul,:
cylinder. On the other hand, the pure stretching plays a more important role
with increasing angle of attack of a streamline body. Elucidation of the rela-
tive significance of pure stretching and tilting-induced stretching depending
upon the bluffness of the body and its angle of attack is a matter of prime inter-
est insofar as the turbulence amplification is concerned. An analysis of the im-
portance and role of these two governing factors in flow about an airfoil has
therefore been initiated.
The amplified turbulence is the agent responsible for changing the nature
of the body boundary layer and for retarding the separation at subcritical Rey-
nolds numbers (see Semi-Annual Status Report, 1 April 1978-30 September 1978).
4This mechanism is discussed in detail in the forthcoming technical report on
separation on a circular cylinder.
2.3 Analytical work
During the subject six-month period the emphasis was placed on the experi-
mental program and, consequently, only a limited effort was devoted to the
analytical work. The critical evaluation of the rapid-distortion and vorticity-
amplification theories was pursued. An analysis of the rapid-distortion theory
including its applications and limitations was completed. Concurrently, an in-
depth review of the vorticity-amplification theory and its extension to the
flow about an airfoil have been initiated. The matching scheme of the inner and
outer solutions of the vorticity-amplification theory has further been explored
using several numerical methods.
3.	 Other Activities
A.	 Publications completed under this grant:
1. "A Visual Investigation of Turbulence in Stagnation Flow About a Cir-
cular Cylinder," (with Brauer, H. J.), NASA CR-3019, October 1978.
2. Ibid. 1, in process of publication in the Journal of Fluid Mechanics.
3. "Visualization of Turbulence in. Flow About a Bluff Body," (with
Brauer, H. J.), to be published in the Proceedings of the ASME Sympo-
sium on Aerodynamics of Transportation, Niagara Falls, New York, 18-
20 June 1979.
4. "Freestream Turbulence Effect on Laminar Separation on a Circular
Cylinder," (with Brauer, H. J. and Sullivan, P. P.), accepted for pre-
sentation at and preprint publication of the AIAA 12th Fluid and Plasma
Dynamics Conference, Williamsburg, Virginia, 23-25 July 1979.
S.	 "A Method for Determining the Weak Statistical Stationarity of a Random
Process," (with Koper, C. A., Jr.), AIAA Journal, 16, 11, 1196-1202,
November 1978.
6. "Turbulent Transport in the Lower Atmosphere," (with Koper, C. A., Jr.),
Proceedings, 15th Annual Meeting of the Society of Engineering Science,
University of Florida, Gainesville, Florida, 4-6 December 1978, 4 era-
kowski, R. L., ed., 393-398, University of Florida, Gainesville, Florida,
Division of Continuing Education Publication, December 1978.
7. "Investigation of Turbulent Diffusion in the Extreme Lower Atmosphere,"
(with Koper, C. A., Jr.), Preprints Proceedings, 4th Symposium on Tur-
bulence, Diffusion and Air Pollution, American Meteorological Society,
Reno, Nevada, 15-18 January 1979, 665-672, American Meteorological
Society, Boston, Massachusetts, January 1979.
F
5Reprints of papers nos. S and 7 are enclosed. Papers nos. 5-7 resulted
from a research program conducted earlier under a NASA Marshall Space Flight
Center Contract NAS8-28S90. The subject two papers were completed under the
current NASA Lewis Research Center grant.
B.	 Lectures delivered by the principal investigator
1. "Turbulent Transport in the Lower Atmosphere," Society of Engineering
Science 15th Annual Meeting, University of Florida, Gainesville, Florida,
4-6 December 1978.
2. "Investigation of Turbulent Diffusion in the Extreme Lower Atmosphere,"
AMS 4th Symposium on Turbulence, Diffusion and Air Pollution, Reno,
Nevada, 15-18 January 1979.
C.	 Miscellaneous
The principal investigator was elected to the New York Academy of
Sciences in recognition of his achievements.
.~. i[~ IIi: II I' \" ~i ;. ~~ ¥ ~, I', " 1! 
- ul 
1.
8 
,.
. 
•
 .
.
.
,
.
.
-
-
-
r-
--
-_
 
1
-
'
-
8
 
I , 
1
.6
1
: 
"
"
"
'c
l 
XI
 =
 x
ll
c 
.
.
 
! 
=
8
/c
 
i2
0=
 0
.5
 
~
 
ul 
1.6
1 
8
1 
V
..
--
-t
--
n-
--
I 
~
 
J 
1.
4L
I-
--
JI
~-
+-
-
~
 
I 
1.
2 
L I o 
0.
00
2 
0.
00
4 
0.
00
6 
-X
I 
U
I_
 0.
00
8 
c 
=
 1
22
cm
 
5 
Re
e=
 
10
 
_
 
,
.
.
.
 
8 
=
 3
.0
5m
m
 
~ =
 
u~ (
X
I)
 
I 
-o~
--~
 
1.
0 
I 
_
 u~
 (
i l
=
0.
06
25
) 
~
 (x
I=
7.
62
cm
) 
=
 
83
.1
 c
m
l/s
Z 
0.
8 0
 
0.
01
 
0.
02
 
.
0.
03
 
0.
04
 
0.
05
 
0.
06
 
0.
07
 
- x
I 
Fi
g.
 1
. 
A
m
pl
if
ic
at
io
n 
o
f 
th
e 
st
re
am
w
is
e 
tu
rb
ul
en
t 
e
n
e
rg
y 
in
 f
lo
w
 a
bo
ut
 a
 
sy
m
m
et
ric
 
NA
CA
 6
5-
01
0 
a
ir
fo
il
. 
5.
0_
 
.
 
-
~8
 
-
2 
( ul
 (~
) )
0 
=
 
U2
 ( ~
) 
o
t 
12
 =
 
0.
37
5 
4
.o
W
l 
- ~2
= 
~2
/c
 
-
~2
(m
m)
 
AZ
 
3.
0 
Q 
-
4 
0.
00
32
 
ul 
(~
) 
[J
 
10
 
0.
00
82
 
o
 
20
 
0.
0 
16
4 
( u
l (
~»
o 
o
 
40
 
0.
03
27
 
2.
0 1.0
~ 
~
 
I 
I 
; 
I ~ 
I 
0
1 
=
-r:
 
±
 
y 
I Q
 
I 
o
 
0.
01
 
0
.0
2
· 
0.
03
 
0.
04
 
0.
05
 
0.
06
 
0.
07
 
- X
z 
Fi
g.
 
2.
 
A
m
pl
if
ic
at
io
n 
o
f 
di
sc
re
te
 t
u
rb
ul
en
t 
e
n
e
rg
y 
a
t 
fo
ur
 s
e
le
ct
ed
 s
c
a
le
s 
in
 f
lo
w
 a
bo
ut
 
a 
sy
m
m
et
ri
c 
NA
CA
 6
5-
01
0 
a
ir
fo
il
. 


Effects of turbulence on laminar separation on aerodynamic surfaces such as airfoils and compressor blading

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server