This paper describes the change in the transition mechanism of a separated boundary layer formed from the semicircular leading-edge of a constant thickness airfoil as the free-stream turbulence (fst) increases. Experiments are carried out in a low-speed wind tunnel for three levels of fst (Tu = 0.65%, 4.6%, and 7.7%) at two Reynolds numbers (Re) 25,000 and 55,000 (based on the leading-edge diameter). Measurements of velocity and surface pressure along with flow field visualizations are carried out using a planar particle image velocimetry (PIV). The flow undergoes separation in the vicinity of leading-edge and reattaches in the downstream forming a separation bubble. The shear layer is laminar up to 20% of separation length, and then, the perturbations are amplified in the second-half attributing to breakdown and reattachment. The bubble length is highly susceptible to change in Tu. At low fst, the primary mode of instability of the shear layer is Kelvin–Helmholtz (K-H), although the local viscous effect may not be neglected. At high fst, the mechanism of shear layer rollup is bypassed with transient growth of perturbations along with evidence of spot formation. The predominant shedding frequency when normalized with respect to the momentum thickness at separation is almost constant and shows a good agreement with the previous studies. After reattachment, the flow takes longer length to approach a canonical boundary layer.
Issue Section:
Fundamental Issues and Canonical Flows
References
1.
Horton
, H. P.
, 1968
, “Laminar Separation Bubbles in Two and Three Dimensional Incompressible Flow
,” Ph.D. thesis, Department of Aeronautical Engineering, Queen Mary College, University of London, London.2.
Gaster
, M.
, 1967
, “The Structure and Behaviour of Laminar Separation Bubbles
,” Aerodynamics Division N.P.L., Ministry of Technology, London, Reports and Memoranda No. 3595.3.
Cherry
, N. J.
, Hiller
, R.
, and Latour
, M. E. M. P.
, 1984
, “Unsteady Measurements in a Separated and Reattaching Flow
,” J. Fluid Mech.
, 144
, pp. 13
–46
.4.
Watmuff
, J. H.
, 1999
, “Evolution of a Wave Packet Into Vortex Loops in a Laminar Separation Bubble
,” J. Fluid Mech.
, 397
, pp. 119
–169
.5.
Talan
, M.
, and Hourmouziadis
, J.
, 2002
, “Characteristic Regimes of Transitional Separation Bubbles in Unsteady Flow
,” Flow, Turbul. Combust.
, 69
(3–4
), pp. 207
–227
.6.
Dahnert
, J.
, Lyko
, C.
, and Peitsch
, D.
, 2013
, “Transition Mechanisms in Laminar Separated Flow Under Simulated Low Pressure Turbine Aerofoil Conditions
,” ASME J. Turbomach.
, 135
(1
), p. 011007
.7.
Yarusevych
, S.
, Sullivan
, E. P.
, and Kawall
, G. J.
, 2009
, “On Vortex Shedding From an Airfoil in Low-Reynolds-Number Flows
,” J. Fluid Mech.
, 632
, pp. 245
–271
.8.
Schobeiri
, M. T.
, Ozturk
, B.
, and Ashpis
, E. D.
, 2007
, “Effect of Reynolds Number and Periodic Unsteady Wake Flow Condition on Boundary Layer Development, Separation, and Intermittency Behavior Along the Suction Surface of a Low Pressure Turbine Blade
,” ASME J. Turbomach.
, 129
(1
), pp. 92
–107
.9.
Satta
, F.
, Simoni
, D.
, Ubaldi
, M.
, Zunino
, P.
, and Bertini
, F.
, 2010
, “Experimental Investigation of Separation and Transition Process on a High Lift Low-Pressure Turbine Profile Under Steady and Unsteady Inflow at Low Reynolds Number
,” J. Therm. Sci.
, 19
(1
), pp. 26
–33
.10.
McAuliffe
, B. R.
, and Yaras
, M. I.
, 2005
, “Separation-Bubble-Transition Measurements on a Low-Re Airfoil Using Particle Image Velocimetry
,” ASME
Paper No. GT2005-68663. 11.
Hain
, R.
, Kahler
, C. J.
, and Radespiel
, R.
, 2009
, “Dynamics of Laminar Separation Bubbles at Low-Reynolds-Number Aerofoils
,” J. Fluid Mech.
, 630
, pp. 129
–153
.12.
Hu
, H.
, and Yang
, Z.
, 2008
, “An Experimental Study of the Laminar Flow Separation on a Low-Reynolds-Number Airfoil
,” ASME J. Fluids Eng.
, 130
(5
), p. 051101
.13.
Lin
, J. C. M.
, and Pauley
, L. L.
, 1996
, “Low-Reynolds Number Separation on an Airfoil
,” AIAA J.
, 34
(8
), pp. 1570
–1577
.14.
Robert
, S. K.
, and Yaras
, M. I.
, 2005
, “Boundary Layer Transition Affected by Surface Roughness and Free-Stream Turbulence
,” ASME J. Fluids Eng.
, 127
(3
), pp. 449
–457
.15.
Sarkar
, S.
, and Voke
, P.
, 2006
, “Large-Eddy Simulation of Unsteady Surface Pressure Over a Low-Pressure Turbine Blade Due to Interactions of Passing Wakes and Inflectional Boundary Layer
,” ASME J. Turbomach.
, 128
(2
), pp. 221
–231
.16.
Spalart
, P. R.
, and Strelets
, M. K.
, 2000
, “Mechanisms of Transition and Heat Transfer in a Separation Bubble
,” J. Fluid Mech.
, 403
, pp. 329
–349
.17.
Alam
, M.
, and Sandham
, N. D.
, 2000
, “Direct Numerical Simulation of Short Laminar Separation Bubbles With Turbulent Reattachment
,” J. Fluid Mech.
, 410
, pp. 1
–28
.18.
Yang
, Z. Y.
, and Voke
, P. R.
, 2001
, “Large-Eddy Simulation of Boundary Layer Separation and Transition at a Change of Surface Curvature
,” J. Fluid Mech.
, 439
, pp. 305
–333
.19.
Sarkar
, S.
, 2008
, “Identification of Flow Structures on a LP Turbine Blade Due to Periodic Passing Wakes
,” ASME J. Fluids Eng.
, 130
(6
), p. 061103
.20.
Sarkar
, S.
, 2009
, “Influence of Wake Structure on Unsteady Flow in an LP Turbine Blade Passage
,” ASME J. Turbomach.
, 131
(4
), p. 041016
.21.
Hiller
, R.
, and Cherry
, N. J.
, 1981
, “The Effects of Stream Turbulence on Separation Bubbles
,” J. Wind Eng. Ind. Aerodyn.
, 8
(1–2
), pp. 49
–58
.22.
Volino
, J. R.
, and Hultgren
, S. L.
, 2001
, “Measurements in Separated and Transitional Boundary Layers Under Low-Pressure Turbine Airfoil Conditions
,” ASME J. Turbomach.
, 123
(2
), pp. 189
–197
.23.
Volino
, R. J.
, 2002
, “Separated Flow Transition Under Simulated Low-Pressure Turbine Airfoil Conditions—Part 1: Mean Flow and Turbulence Statistics
,” ASME J. Turbomach.
, 124
(4
), pp. 645
–655
.24.
McAuliffe
, B. R.
, and Yaras
, M. I.
, 2010
, “Transition Mechanisms in Separation Bubbles Under Low and Elevated Free-Stream Turbulence
,” ASME J. Turbomach.
, 132
(1
), p. 011004
.25.
Langari
, M.
, and Yang
, Z.
, 2013
, “Numerical Study of the Primary Instability in a Separated Boundary Layer Transition Under Elevated Free-Stream Turbulence
,” Phys. Fluids
, 25
(7
), p. 074106
.26.
Halstead
, D. E.
, Wisler
, D. C.
, Okiishi
, T. H.
, Walker
, G. J.
, Hodson
, H. P.
, and Shin
, H.-W.
, 1997
, “Boundary Layer Development in Axial Compressors and Turbines: Part 1 of 4—Composite Picture
,” ASME J. Turbomach.
, 119
(1
), pp. 114
–127
.27.
Solomon
, W. J.
, 2000
, “Effects of Turbulence and Solidity on the Boundary Layer Development in a Low Pressure Turbine
,” ASME
Paper No. 2000-GT-0273. 28.
Tennekes
, H.
, and Lumley
, J. L.
, 1972
, A First Course in Turbulence
, The MIT Press
, Cambridge, MA.29.
Oberlack
, M.
, 2002
, “On the Decay Exponent of Isotropic Turbulence
,” Proc. Appl. Math. Mech.
, 1
(1
), pp. 294
–297
.30.
Sharma
, D. M.
, and Poddar
, K.
, 2010
, “Investigations on Quasi-Steady Characteristics for an Airfoil Oscillating at Low Reduced Frequencies
,” Int. J. Aerosp. Eng.
, 2010
, p. 940528
.31.
Yavuzkurt
, S.
, 1984
, “A Guide to Uncertainty Analysis of Hot-Wire Data
,” ASME J. Fluids Eng.
, 106
(2
), pp. 181
–186
.32.
Bradshaw
, P.
, 1971
, An Introduction to Turbulence and Its Measurement
, Pergamon Press
, Oxford
.33.
Roshko
, A.
, and Lau
, J. K.
, 1965
, “Some Observations on Transition and Reattachment of a Free Shear Layer in Incompressible Flow
,” Proc. Heat Transfer, Fluid Mech., Inst.
, 18
, pp. 157
–167
.34.
Gerakopulous
, R.
, Boutilier
, M. S. H.
, and Yarusevych
, S.
, 2010
, “Aerodynamic Characterisation of a NACA 0018 Airfoil at Low Reynolds Numbers
,” AIAA
Paper No. 2010-4629. 35.
Stevenson
, J. P. J.
, Walsh
, E. J.
, Nolan
, K. P.
, and Davies
, M. R. D.
, 2014
, “Separation & Free-Stream Turbulence: Implications for Surface Aerodynamics & Heat Transfer
,” J. Phys.: Conf. Ser.
, 525
(1
), p. 012018
.36.
Dovgal
, A.
, Kozlov
, V.
, and Michalke
, A.
, 1994
, “Laminar Boundary Layer Separation: Instability and Associated Phenomena
,” Prog. Aerosp. Sci.
, 30
(1
), pp. 61
–94
.37.
Kaun
, C. L.
, and Wang
, T.
, 1990
, “Investigation of the Intermittent Behavior of Transitional Boundary Layer Using a Conditional Averaging Technique
,” Exp. Therm. Fluid Sci.
, 3
(2
), pp. 157
–173
.38.
Hedley
, T. B.
, and Keffer
, J. F.
, 1974
, “Turbulent/Non-Turbulent Decisions in an Intermittent Flow
,” J. Fluid Mech.
, 64
(4
), pp. 625
–644
.39.
Dhawan
, S.
, and Narasimha
, R.
, 1958
, “Some Properties of Boundary Layer Flow During the Transition From Laminar to Turbulent Motion
,” J. Fluid Mech.
, 3
(4
), pp. 418
–436
.40.
Butler
, K. M.
, and Farrell
, B. F.
, 1992
, “Three-Dimensional Optical Disturbances in Viscous Shear Flow
,” Phys. Fluids A
, 4
(8
), pp. 1637
–1650
.41.
Jacobs
, R. G.
, and Durbin
, P. A.
, 2001
, “Simulations of Bypass Transition
,” J. Fluid Mech.
, 428
, pp. 185
–212
.42.
Emmons
, H. W.
, 1951
, “The Laminar-Turbulent Transition in a Boundary Layer—Part I
,” J. Aerosp. Sci.
, 18
(7
), pp. 490
–498
.43.
Mayle
, R. E.
, 1991
, “The Role of Laminar–Turbulent Transition in Gas Turbine Engines
,” ASME J. Turbomach.
, 113
(4
), pp. 509
–536
.44.
Chen
, K. K.
, and Thyson
, N. A.
, 1971
, “Extension of Emmon's Spot Theory to Flows on Blunt Bodies
,” AIAA J.
, 9
(5
), pp. 821
–825
.45.
Ellsworth
, R. H.
, and Mueller
, T. J.
, 1991
, “Airfoil Boundary Layer Measurements at Low Re in an Accelerating Flow From a Nonzero Velocity
,” Exp. Fluids
, 11
(6
), pp. 368
–374
.46.
Luchini
, P.
, 2000
, “Reynolds-Number-Independent Instability of the Boundary Layer Over a Flat Surface
,” J. Fluid Mech.
, 404
, pp. 289
–309
.47.
Matsubara
, M.
, and Alfredsson
, H.
, 2001
, “Disturbance Growth in Boundary Layers Subjected to Free-Stream Turbulence
,” J. Fluid. Mech.
, 430
, pp. 149
–168
.48.
Ol
, M. V.
, Hanff
, E.
, McAuliffe
, B.
, Scholz
, U.
, and Kahler
, C.
, 2005
, “Comparison of Laminar Separation Bubble Measurements on a Low Reynolds Number Airfoil in Three Facilities
,” AIAA
Paper No. 2005-5149. 49.
Chandrasekar
, S.
, 1961
, Hydrodynamic and Hydromagnetic Stability
, Clarendon Press
, Oxford
.50.
Walker
, G. J.
, 1989
, “Transitional Flow on Axial Turbomachine Blading
,” AIAA J.
, 27
(5
), pp. 595
–602
.51.
Abu-Ghannam
, B. J.
, and Shaw
, R.
, 1980
, “Natural Transition of Boundary Layers—The Effects of Turbulence, Pressure Gradient, and Flow History
,” J. Mech. Eng. Sci.
, 22
(5
), pp. 213
–228
.52.
Gostelow
, J. P.
, Blunden
, A. R.
, and Blunden
, W. R.
, 1994
, “Effects of Free-Stream Turbulence and Adverse Pressure Gradients on Boundary Layer Transition
,” ASME J. Turbomach.
, 116
(3
), pp. 392
–404
.53.
Curle
, N.
, and Skan
, S. W.
, 1957
, “Approximate Methods for Predicting Separation Properties of Laminar Boundary Layers
,” Aeronaut. Q.
, 8
, pp. 257
–268
.54.
Thwaites
, B.
, 1949
, “Approximate Calculation of the Laminar Boundary Layer
,” Aeronaut. Q.
, 14
, pp. 61
–85
.55.
Roberts
, W. B.
, 1980
, “Calculation of Laminar Separation Bubbles and Their Effect on Airfoil Performance
,” AIAA J.
, 18
(1
), pp. 25
–31
.56.
Hinze
, J. O.
, 1959
, Turbulence
, McGraw-Hill
, New York
.57.
Hatman
, A.
, and Wang
, T.
, 1999
, “A Prediction Model for Separated-Flow Transition
,” ASME J. Turbomach.
, 121
(3
), pp. 594
–602
.58.
Praisner
, T. J.
, and Clark
, J. P.
, 2007
, “Predicting Transition in Turbomachinery—Part I: A Review and New Model Development
,” ASME J. Turbomach.
, 129
(1
), pp. 1
–13
.59.
Davis
, R. L.
, Carter
, J. E.
, and Reshotko
, E.
, 1987
, “Analysis of Transitional Separation Bubbles on Infinite Swept Wings
,” AIAA J.
, 25
(3
), pp. 421
–428
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