A pressure distribution representative of a controlled diffusion compressor blade suction surface is imposed on a flat plate. Boundary layer transition in this situation is investigated by triggering a wave packet, which evolves into a turbulent spot. The development from wave packet to turbulent spot is observed and the interactions of the turbulent spot with the ongoing natural transition and the ensuing turbulent boundary layer are examined. Under this steeply diffusing pressure distribution, strong amplification of primary instabilities prevails. Breakdown to turbulence is instigated near the centerline and propagates transversely along the wave packet until the turbulent region dominates. An extensive calmed region is present behind the spot, which persists well into the surrounding turbulent layer. Celerities of spot leading and trailing edges are presented, as is the spanwise spreading half-angle. Corresponding measurements for spots under a wide range of imposed pressure gradients are compiled and the present results are compared with those of other authors. Resulting correlations for spot propagation parameters are provided for use in computational modeling of the transition region under variable pressure gradients.

1.
Chen
K. K.
, and
Thyson
N. A.
,
1971
, “
Extension of Emmons’ Spot Theory to Flows on Blunt Bodies
,”
AIAA Journal
, Vol.
9
, No.
5
, pp.
821
825
.
2.
Cohen
J.
,
Breuer
K. S.
, and
Haritonidis
J. H.
,
1991
, “
On the Evolution of a Wave Packet in a Laminar Boundary Layer
,”
Journal of Fluid Mechanics
, Vol.
225
, pp.
575
606
.
3.
Emmons
H. W.
,
1951
, “
The Laminar–Turbulent Transition in a Boundary Layer—Part 1
,”
Journal of Aero. Sciences
, Vol.
18
, No.
7
, pp.
490
498
.
4.
Gostelow, J. P., Hong, G., Melwani, N., and Walker, G. J., 1993, “Turbulent Spot Development Under a Moderate Adverse Pressure Gradient,” ASME Paper No. 93-GT-377.
5.
Gostelow
J. P.
,
Blunden
A. R.
, and
Walker
G. J.
,
1994
, “
Effects of Free-Stream Turbulence and Adverse Pressure Gradients on Boundary Layer Transition
,”
ASME JOURNAL OF TURBOMACHINERY
, Vol.
116
, pp.
392
404
.
6.
Gutmark
E.
, and
Blackwelder
R. F.
,
1987
, “
On the Structure of a Turbulent Spot in a Heated Laminar Boundary Layer
,”
Experiments in Fluids
, Vol.
5
, pp.
217
229
.
7.
Johnson
M. W.
,
1994
, “
A Bypass Transition Model for Boundary Layers
,”
ASME JOURNAL OF TURBOMACHINERY
, Vol.
116
, pp.
759
764
.
8.
Katz
Y.
,
Seifert
A.
, and
Wygnanski
I.
,
1990
, “
On the Evolution of the Turbulent Spot in a Laminar Boundary Layer With a Favourable Pressure Gradient
,”
Journal of Fluid Mechanics
, Vol.
221
, pp.
1
22
.
9.
Narasimha
R.
,
1957
, “
On the Distribution of Intermittency in the Transition Region of a Boundary Layer
,”
Journal of Aero. Sciences
, Vol.
24
, No.
9
, pp.
711
712
.
10.
Schubauer, G. B., and Klebanoff, P. S., 1955, “Contributions on the Mechanics of Boundary-Layer Transition,” NACA Rep. 1289.
11.
Seifert, A., and Wygnanski, I. J., 1994, “On Turbulent Spots in a Laminar Boundary Layer Subjected to a Self-Similar Adverse Pressure Gradient,” private communication.
12.
Sankaran, M., Chambers, A. J., and Antonia, R. A., 1986, “The Influence of a Favourable Pressure Gradient on the Growth of a Turbulent Spot,” Proc. 9th Australasian Fluid Mechanics Conference, Auckland, pp. 342–345.
13.
Solomon
W. J.
,
Walker
G. J.
, and
Gostelow
J. P.
,
1996
, “
Transition Length Prediction for Flows With Rapidly Changing Pressure Gradients
,”
ASME JOURNAL OF TURBOMACHINERY
, Vol.
118
, pp.
744
751
.
14.
van Hest, B. F. A., Pesschier, D. M., and van Ingen, J. L., 1994, “The Development of a Turbulent Spot in an Adverse Pressure Gradient Boundary Layer,” Proc. IUTAM Symposium, Sendai, Japan.
15.
Walker
G. J.
, and
Gostelow
J. P.
,
1990
, “
Effects of Adverse Pressure Gradients on the Nature and Length of Boundary Layer Transition
,”
ASME JOURNAL OF TURBOMACHINERY
, Vol.
112
, pp.
196
205
.
16.
Walker, G. J., Solomon, W. J., and Gostelow, J. P., 1993, “Observations of Wake-Induced Turbulent Spots on an Axial Compressor Blade,” ASME Paper No. 93-GT-378.
17.
Watmuff, J. H., 1991, “An Experimental Investigation of Boundary Layer Transition in an Adverse Pressure Gradient,” Proc. ASME Symposium, Boundary Layer Stability and Transition to Turbulence, Portland, OR, pp. 129–136.
18.
Wills
J. A. B.
,
1962
, “
Correction of Hot Wire Readings for Proximity to a Solid Boundary
,”
Journal of Fluid Mechanics
, Vol.
12
, pp.
388
396
.
19.
Wygnanski
I.
,
1981
, “
The Effect of Reynolds Number and Pressure Gradient on the Transitional Spot in a Laminar Boundary Layer
,”
Lecture Notes in Physics
: The Role of Coherent Structures in Modelling Turbulence and Mixing, Vol.
136
, p.
304
304
.
20.
Wygnanski
I.
,
Zilberman
M.
, and
Haritonidis
J. H.
,
1982
, “
On the Spreading of a Turbulent Spot in the Absence of a Pressure Gradient
,”
Journal of Fluid Mechanics
, Vol.
123
, pp.
69
90
.
This content is only available via PDF.
You do not currently have access to this content.