The present study formulates an improved approach for analyzing separated-flow transition that differentiates between the transition process in boundary layers that are laminar at separation and those that are already transitional at separation. The paper introduces new parameters that are necessary in classifying separated-flow transition modes and in accounting for the concomitant evolution of transition in separated shear layer and the average effect of periodic separation bubble build-up and vortex shedding. At least three separated-flow transition modes are positively distinguished: (a) transitional separation, with the transition starting upstream of the separation point and developing mostly as natural transition, (b) laminar separation/short bubble mode, with the onset of transition induced downstream of the separation point by inflexional instability and with a quick transition completion, and (c) laminar separation/long bubble mode, with the onset of transition also induced downstream of the separation point by inflexional instability, and with the transition completion delayed. Passing from one mode to another takes place continuously through a succession of intermediate stages. The location of maximum bubble elevation has been proved to be the controlling parameter for the separated flow behavior. It was found that, downstream of the separation point, the experimental data expressed in terms of distance Reynolds number Rex can be correlated better than momentum or displacement thickness Reynolds number. For each mode of separated-flow transition, the onset of transition, the transition length, and separated flow general characteristic are determined. This prediction model is developed mainly on low free-stream turbulence flat plate data and limited airfoil data. Extension to airfoils and high turbulence environment requires additional study.

1.
Brendel, M., and Mueller, T. J., 1987, “Boundary Layer Measurements on an Airfoil at Low Reynolds Numbers,” AIAA Paper No. 87-0495.
2.
Fitzgerald
E. G.
, and
Mueller
T. J.
,
1989
, “
Measurements in a Separation Bubble on an Airfoil Using Laser Velocimetry
,”
AIAA J.
,
28
(
4
),
584
592
.
3.
Gaster, M., 1967, “The Structure and Behavior of Separation Bubble,” NPL Reports and Memoranda No. 3595.
4.
Gleyzes, C., Cousteix, J., and Bonnet, J. L., 1980, “Flow Visualization of Leading Edge Separation Bubbles,” International Symposium of Flow Visualization, Bochum, 1979, pp. 198–203.
5.
Hatman, A., 1997, “Laminar–Turbulent Transition in Separated Boundary Layers,” Ph.D. Dissertation, Department of Mechanical Engineering, Clemson University, Clemson, SC.
6.
Hatman, A., and Wang, T., 1998a, “Separated-Flow Transition, Part 1—Experimental Methodology,” ASME Paper No. 98-GT-461.
7.
Hatman, A., and Wang, T., 1998b, “Separated-Flow Transition, Part 2—Experimental Results,” ASME Paper No. 98-GT-462.
8.
Hatman, A., and Wang, T., 1998c, “Separated-Flow Transition, Part 3—Primary Modes and Vortex Dynamics,” ASME Paper No. 98-GT-463.
9.
Hazarika
B. K.
, and
Hirsch
C.
,
1997
, “
Transition Over C4 Leading Edge and Measurement of Intermittency Factor Using PDF of Hot-Wire Signal
,”
ASME JOURNAL OF TURBOMACHINERY
, Vol.
119
, pp.
412
425
.
10.
Hoheisel, H., et al., 1984, “A Comparison of Laser-Doppler Anemometry and Probe Measurements Within the Boundary Layer of an Airfoil at Subsonic Flow,” Laser Anemometry in Fluid Mechanics—II, Selected Papers from 2nd International Symposium on Applications of Laser Anemometry to Fluid Mechanics, Lisbon, Portugal.
11.
Horton, H. P., 1968, “A Semi-Empirical Theory for the Growth and Bursting of Laminar Separation Bubbles,” Aeronautical Research Council, CP-1073.
12.
Kuan
C. L.
, and
Wang
T.
,
1990
, “
Investigation of the Intermittent Behavior of Transitional Boundary Layer Using a Conditional Averaging technique
,”
Experimental Thermal and Fluid Science
, Vol.
3
, pp.
157
173
.
13.
Kwon
O. K.
, and
Pletcher
R. H.
,
1979
, “
Prediction of Incompressible Separated Boundary Layers Including Viscous–Inviscid Interaction
,”
ASME Journal of Fluids Engineering
, Vol.
101
, pp.
466
472
.
14.
Malkiel
E.
, and
Mayle
R. E.
,
1996
, “
Transition in a Separation Bubble
,”
ASME JOURNAL OF TURBOMACHINERY
, Vol.
118
, pp.
752
759
.
15.
Mayle
R. E.
,
1991
, “
The Role of Laminar–Turbulent Transition in Gas Turbine Engines
,”
ASME JOURNAL OF TURBOMACHINERY
, Vol.
113
, pp.
509
537
.
16.
Mislevy
S. P.
, and
Wang
T.
,
1996
, “
The Effects of Adverse Pressure Gradients on Momentum and Thermal Structures in Transitional Boundary Layers; Part 1—Mean Quantities, Part 2; Fluctuating Quantities
,”
ASME JOURNAL OF TURBOMACHINERY
, Vol.
118
, pp.
717
736
.
17.
Morkovin, M. V., 1991, “Panoramic view of changes in vorticity distribution in transition instabilities and turbulence,” Instability, Transition and Turbulence, Hussaini & Kumar, eds., pp. 1–12.
18.
Roberts, W. B., 1980, “Calculation of Laminar Separation Bubbles and Their Effect on Airfoil Performance,” AIAA J., Vol. 18.
19.
Schmidt
G. S.
, and
Mueller
T. J.
,
1989
, “
Analysis of Low Reynolds Number Separation Bubbles Using Semi-empirical Methods
,”
AIAA J.
,
27
(
8
),
993
1001
.
20.
Tani
I.
,
1964
, “
Low Speed Flows Involving Bubble Separations
,”
Progress in Aeronautical Sciences
, Vol.
5
, pp.
70
104
.
21.
van Ingen, J. L., 1977, “On the Calculation of Laminar Separation Bubbles in Two Dimensional Incompressible Flow,” AGARD, CP 168, No. 11.
22.
Walker, G. J., Subroto, P. H., and Platzer, M. F., 1988, “Transition Modeling Effects and Viscous/Inviscid Interaction Analysis of Low Reynolds Number Airfoil Flows Involving Laminar Separation Bubbles,” ASME Paper No. 88-GT-32.
23.
Walker, G. J., 1989, “Modeling of Transitional Flow in Laminar Separation Bubbles,” Proc. 9th International Symposium on Air Breathing Engines, Athens, pp. 539–548.
24.
Walker
G. J.
,
1993
, “
The Role of Laminar–Turbulent Transition in Gas Turbine Engines: A Discussion
,”
ASME JOURNAL OF TURBOMACHINERY
, Vol.
115
, pp.
207
217
.
25.
Young, A. D., and Horton, H. P., 1966, “Some Results of Investigations of Separation Bubbles,” AGARD CP 4, pp. 779–811.
26.
Zhou, D., and Wang, T., 1992, “Laminar Boundary Layer Flow and Heat Transfer With Favorable Pressure Gradient at Constant K Values,” ASME Paper No. 92-GT-246.
This content is only available via PDF.
You do not currently have access to this content.