An experimental investigation of free stream turbulence (FST) induced disturbances in asymptotic suction boundary layers (ASBL) has been performed. In the present study four different suction rates are used and the highest is 0.40% of the free stream velocity, together with three different FST levels (Tu=1.6, 2.0, and 2.3%). A turbulence generating grid of the active type is used and offers the possibility to vary the Tu-level while the scales of the turbulence remain almost constant. It is known that FST induces elongated disturbances consisting of high and low velocity regions, usually denoted streaky structures, into the boundary layer. The experiments show that wall suction suppresses the disturbance growth and may significantly delay or inhibit the break-down to turbulence. Two-point correlation measurements in the spanwise direction show that the averaged streak spacing decreases with increasing FST-level, whereas the spanwise scale in the ASBL is more or less constant if scaled with the free stream velocity and viscosity. This is in contrast to what is observed in a Blasius boundary layer where streaks develop and adapt their spanwise scale close to the boundary layer thickness.

1.
K. J. A.
Westin
and
R. A. W. M.
Henkes
, “
Application of turbulence models to bypass transition
,”
J. Fluids Eng.
119
,
859
(
1997
).
2.
J. M.
Kendall
, “
Experimental study of disturbances produced in a pre-transitional laminar boundary layer by weak freestream turbulence
,” AIAA Paper 85-1695 (
1985
).
3.
J. M.
Kendall
, “
Experiments on boundary layer receptivity to freestream turbulence
,” AIAA Paper 98-0530 (
1998
).
4.
K. J. A.
Westin
,
A. V.
Boiko
,
B. G. B.
Klingmann
,
V. V.
Kozlov
, and
P. H.
Alfredsson
, “
Experiments in a boundary layer subjected to free-stream turbulence. Part I. Boundary layer structure and receptivity
,”
J. Fluid Mech.
281
,
193
(
1994
).
5.
P. H.
Alfredsson
and
M.
Matsubara
, “
Free-stream turbulence, streaky structures and transition in boundary layer flows
,” AIAA Paper 2000-2534 (
2000
).
6.
M.
Matsubara
and
P. H.
Alfredsson
, “
Disturbance growth in boundary layers subjected to free stream turbulence
,”
J. Fluid Mech.
430
,
149
(
2001
).
7.
P.
Andersson
,
M.
Berggren
, and
D. S.
Henningson
, “
Optimal disturbances and bypass transition in boundary layers
,”
Phys. Fluids
11
,
134
(
1999
).
8.
P.
Luchini
, “
Reynolds-number-independent instability of the boundary layer over a flat surface
,”
J. Fluid Mech.
404
,
289
(
2000
).
9.
J. H. M.
Fransson
and
P.
Corbett
, “
Optimal linear growth in the asymptotic suction boundary layer
,”
Eur. J. Mech. B/Fluids
22
,
259
(
2003
).
10.
P.
Andersson
,
L.
Brandt
,
A.
Bottaro
, and
D. S.
Henningson
, “
On the breakdown of boundary layer streaks
,”
J. Fluid Mech.
428
,
29
(
2001
).
11.
K. J. A.
Westin
,
A. A.
Bakchinov
,
V. V.
Kozlov
, and
P. H.
Alfredsson
, “
Experiments on localized disturbances in a flat plate boundary layer. Part 1: The receptivity and evolution of a localized free stream disturbance
,”
Eur. J. Mech. B/Fluids
17
,
823
(
1998
).
12.
J. H. M.
Fransson
and
P. H.
Alfredsson
, “
On the disturbance growth in an asymptotic suction boundary layer
,”
J. Fluid Mech.
482
,
51
(
2003
).
13.
H.
Schlichting
, Boundary Layer Theory (McGraw-Hill, New York,
1979
).
14.
J. H. M.
Fransson
, “
Investigation of the asymptotic suction boundary layer
,” KTH Mechanics, Licentiate thesis, TRITA-MEK 2001:11,
2001
.
15.
A. V.
Johansson
and
P. H.
Alfredsson
, “
On the structure of turbulent channel flow
,”
J. Fluid Mech.
122
,
295
(
1982
).
16.
T. B.
Hedley
and
J. F.
Keffer
, “
Turbulent/non-turbulent decisions in an intermittent flow
,”
J. Fluid Mech.
64
,
625
(
1974
).
This content is only available via PDF.
You do not currently have access to this content.