Research Papers: Fundamental Issues and Canonical Flows

Features of a Laminar Separated Boundary Layer Near the Leading-Edge of a Model Airfoil for Different Angles of Attack: An Experimental Study

[+] Author and Article Information
K. Anand

Department of Mechanical Engineering,
Indian Institute of Technology Kanpur,
Kanpur, Uttar Pradesh 208016, India

S. Sarkar

Department of Mechanical Engineering,
Indian Institute of Technology Kanpur,
Kanpur, Uttar Pradesh 208016, India
e-mail: subra@iitk.ac.in

1Present address: Department of Mechanical Engineering, SASTRA University, Thanjavur, Tamilnadu 613 401, India.

2Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received October 7, 2015; final manuscript received August 26, 2016; published online November 3, 2016. Editor: Malcolm J. Andrews.

J. Fluids Eng 139(2), 021201 (Nov 03, 2016) (14 pages) Paper No: FE-15-1723; doi: 10.1115/1.4034606 History: Received October 07, 2015; Revised August 26, 2016

The evolution of a separated boundary layer over a model airfoil with semicircular leading-edge has been illustrated for angles of attack (α) varying from −3 deg to 10 deg, where the Reynolds number (Rec) based on chord is 1.6 × 105 and the inlet freestream turbulence (fst) being 1.2%. The features of boundary layer are described through measurements of velocity and surface pressure besides the flow visualization using a planar particle image velocimetry (PIV). Freestream perturbations are amplified because of enhanced receptivity of the separated boundary layer resulting in pockets of disturbances, which then propagate downstream attributing to random fluctuations near the reattachment. The separation and reattachment locations including the onset and end of transition are identified for changing α. The reattachment point changes from 18.8% to 47.7% of chord with the onset of separation at almost 7%, whereas the onset of transition moves upstream from 13.2% to 9% with increasing α. The bubble bursting occurs at α = 10 deg. The transition in the separated boundary layer occurs through Kelvin–Helmholtz (K–H) instability for α = 0 deg and 3 deg, whereas the K–H mechanism is bypassed for higher α with significant viscous effect.

Copyright © 2017 by ASME
Your Session has timed out. Please sign back in to continue.


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.
Jones, B. M. , 1934, “ Stalling,” J. R. Aeronaut. Soc., 38(285), pp. 753–770. [CrossRef]
Roshko, A. , and Lau, J. K. , 1965, “ Some Observations on Transition and Reattachment of a Free Shear Layer in Incompressible Flow,” Proceedings of the 1965 Heat Transfer and Fluid Mechanics Institute, Stanford University Press, Stanford, CA, Vol. 18, pp. 157–167.
Gaster, M. , 1969, “ The Structure and Behaviour of Laminar Separation Bubbles,” Aeronautical Division N.P.L., Ministry of Technology, London, Reports and Memoranda No. 3595.
Horton, H. P. , 1968, “ Laminar Separation Bubbles in Two and Three-Dimensional Incompressible Flow,” Ph.D. thesis, University of London, London.
Roberts, W. B. , 1980, “ Calculation of Laminar Separation Bubbles and Their Effect on Aerofoil Performance,” AIAA J., 18(1), pp. 25–31. [CrossRef]
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. [CrossRef]
Arena, A. V. , and Mueller, T. J. , 1980, “ Laminar Separation, Transition, and Turbulent Reattachment Near the Leading Edge of Airfoils,” AIAA J., 18(7), pp. 747–753. [CrossRef]
Watmuff, J. H. , 1999, “ Evolution of a Wave Packet Into Vortex Loops in a Laminar Separation Bubble,” J. Fluid Mech., 397, pp. 119–169. [CrossRef]
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. [CrossRef]
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. [CrossRef]
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. [CrossRef]
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.
Samson, A. , and Sarkar, S. , 2016, “ An Experimental Investigation of a Laminar Separation Bubble on the Leading-Edge of a Modelled Aerofoil for Different Reynolds Numbers,” Proc. Inst. Mech. Eng., Part C, 230(13), pp. 2208–2224. [CrossRef]
Samson, A. , and Sarkar, S. , 2016, “ Effects of Free-Stream Turbulence on Transition of a Separated Boundary Layer Over the Leading-Edge of a Constant Thickness Aerofoil,” ASME J. Fluids Eng., 138(2), p. 021202. [CrossRef]
Pauley, L. , Moin, P. , and Reynolds, W. C. , 1990, “ The Structure of Two-Dimensional Separation,” J. Fluid Mech., 220, pp. 397–411. [CrossRef]
McAuliffe, B. R. , and Yaras, M. I. , 2010, “ Transition Mechanisms in Separation Bubbles Under Low- and Elevated-Freestream Turbulence,” ASME J. Turbomach., 132(1), p. 011004. [CrossRef]
Talan, M. , and Hourmouziadis, J. , 2002, “ Characteristic Regimes of Transitional Separation Bubbles in Unsteady Flow,” Flow, Turbul. Combust., 69(3), pp. 207–227.
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. [CrossRef]
Tafti, D. K. , and Vanka, S. P. , 1991, “ A Three-Dimensional Numerical Study of Flow Separation and Reattachment on a Blunt Plate,” Phys. Fluids, 3(12), pp. 2887–2909. [CrossRef]
Lin, J. C. , and Pauley, L. L. , 1996, “ Low-Reynolds Number Separation on an Airfoil,” AIAA J., 34(8), pp. 1570–1577. [CrossRef]
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. [CrossRef]
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. [CrossRef]
Sarkar, S. , 2007, “ Effects of Passing Wakes on a Separating Boundary Layer Along a Low-Pressure Turbine Blade Through Large-Eddy Simulation,” Proc. Inst. Mech. Eng., Part A, 221(4), pp. 551–564. [CrossRef]
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. [CrossRef]
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. [CrossRef]
Sarkar, S. , Babu, H. , and Sadique, J. , 2016, “ Interactions of Separation Bubble With Oncoming Wakes by LES,” ASME J. Heat Transfer, 138(2), pp. 1645–1656.
McAuliffe, B. R. , and Yaras, M. I. , 2008, “ Numerical Study of Instability Mechanisms Leading to Transition in Separation Bubbles,” ASME J. Turbomach., 130(2), p. 021006. [CrossRef]
Anand, K. , and Sarkar, S. , 2014, “ Experimental Investigation of Separated Shear Layer Over a Flat Plate for Various Angles of Attack and Tail Flat Deflections,” ASME Paper No. GT2014-26113.
Anand, K. , Sarkar, S. , and Thilakan, N. , 2014, “ Experiments on Leading-Edge Induced Separated Shear Layer Under Various Imposed Pressure Gradients,” ASME Paper No. GTINDIA2014-8177.
Yavuzkurt, S. , 1984, “ A Guide to Uncertainty Analysis of Hotwire Data,” ASME J. Fluids Eng., 106(2), pp. 181–186. [CrossRef]
Jeong, J. , and Hussain, F. , 1995, “ On the Identification of a Vortex,” J. Fluid Mech., 285, pp. 69–94. [CrossRef]
Crabtree, L. F. , 1957, “ Effects of Leading-Edge Separation on Thin Wings in Two-Dimensional Incompressible Flow,” J. Aeronaut. Sci., 24(8), pp. 597–604. [CrossRef]
Boutilier, M. S. H. , and Yarusevych, S. , 2012, “ Separated Shear Layer Transition Over an Airfoil at a Low Reynolds Number,” Phys. Fluids, 24(8), p. 084105. [CrossRef]
Peterson, S. D. , and Plesniak, M. W. , 2002, “ Short-Hole Jet-in-Crossflow Velocity Field and Its Relationship to Film-Cooling Performance,” Exp. Fluids, 33(6), pp. 889–898. [CrossRef]
Ol, M. V. , Hanff, E. , McAuliffe, B. , Scholz, U. , and Kaehler, C. , 2005, “ Comparison of Laminar Separation Bubble Measurements on a Low Reynolds Number Airfoil in Three Facilities,” AIAA Paper No. 2005-5149.
Jacobs, R. G. , and Durbin, P. A. , 2001, “ Simulations of Bypass Transition,” J. Fluid Mech., 428, pp. 185–212. [CrossRef]
Dovgal, A. , Kozlov, V. , and Michalke, A. , 1994, “ Laminar Boundary Layer Separation: Instability and Associated Phenomena,” Prog. Aerosp. Sci., 30(1), pp. 61–94. [CrossRef]
Yarusevych, S. , Sullivan, P. , and Kawall, J. G. , 2009, “ On Vortex Shedding From an Airfoil in Low-Reynolds-Number Flows,” J. Fluid Mech., 632, pp. 245–271. [CrossRef]
Chandrasekar, S. , 1961, Hydrodynamic and Hydromagnetic Stability, Clarendon Press, Oxford, UK.
Walker, G. J. , 1989, “ Transitional Flow on Axial Turbomachine Blading,” AIAA J., 27(5), pp. 595–602. [CrossRef]
Corrsin, S. , 1943, “ Investigation of Flow in an Axially Symmetrical Heated Jet of Air,” National Advisory Committee for Aeronautics, Washington, DC, ACR No. 3L23.
Kuan, C. L. , and Wang, T. , 1990, “ Investigation of the Intermittent Behaviour of Transitional Boundary Layer Using a Conditional Averaging Technique,” Exp. Therm. Fluid Sci., 3(2), pp. 157–173. [CrossRef]
Hedley, T. B. , and Keffer, J. F. , 1974, “ Turbulent/Non-Turbulent Decisions in an Intermittent Flow,” J. Fluid Mech., 64(04), pp. 625–644. [CrossRef]
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 Behaviour Along the Suction Surface of a Low Pressure Turbine Blade,” ASME J. Turbomach., 129(1), pp. 92–129. [CrossRef]
Dhawan, S. , and Narasimha, R. , 1958, “ Some Properties of Boundary Layer Flow During the Transition From Laminar to Turbulent Motion,” J. Fluid Mech., 3(04), pp. 418–436. [CrossRef]
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. [CrossRef]
Mayle, R. E. , 1991, “ The Role of Laminar–Turbulent Transition in Gas Turbine Engines,” ASME J. Turbomach., 113(4), pp. 509–537. [CrossRef]
Chen, K. K. , and Thyson, N. A. , 1971, “ Extension of Emmons' Spot Theory to Flows on Blunt Bodies,” AIAA J., 9(5), pp. 821–825. [CrossRef]
Emmon, H. W. , 1951, “ The Laminar-Turbulent Transition in a Boundary Layer—Part I,” J. Aeronaut. Sci., 18(7), pp. 490–498. [CrossRef]
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, pp. 368–374. [CrossRef]
Hatman, A. , and Wang, T. , 1999, “ A Prediction Model for Separated-Flow Transition,” ASME J. Turbomach., 121(3), pp. 594–602. [CrossRef]
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. [CrossRef]
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. [CrossRef]


Grahic Jump Location
Fig. 2

Sketch illustrating a separated boundary layer with onset of separation, transition, and reattachment point on the model airfoil. The origin is the point where the flat portion is blended tangentially with the semicircular leading-edge.

Grahic Jump Location
Fig. 1

Schematic of the tunnel and the model

Grahic Jump Location
Fig. 3

Contours of (a) mean and ((b) and (c)) instantaneous streamwise velocity superimposed with vectors for α = 0 deg

Grahic Jump Location
Fig. 4

Contours of (a) mean and ((b) and (c)) instantaneous streamwise velocity superimposed with vectors for α = 5 deg

Grahic Jump Location
Fig. 5

Contours of (a) mean and (b) instantaneous streamwise velocity superimposed with vectors for α = 10 deg depicting bubble bursting

Grahic Jump Location
Fig. 6

Instantaneous contours of ωz and−λ2 superimposed with velocity fluctuation vectors for α = 0 deg ((a) and (b)) and α = 5 deg ((c) and (d))

Grahic Jump Location
Fig. 7

(a) Variations of surface pressure on the model for various α: Zoomed view indicates that the maximum pressure moves upstream of theoretical stagnation point for high α. (b) Identification of onset of separation, transition, and reattachment for α = 0 deg.

Grahic Jump Location
Fig. 8

Comparison of Cp with data of Arena and Mueller [8] on a similar model configuration

Grahic Jump Location
Fig. 9

Identification of onset of separation, transition, and reattachment from the spatial growth rate of Cp for (a) α = 0 deg and (b) α = 3 deg

Grahic Jump Location
Fig. 10

Variation of laminar shear layer length ll/lb as a function of α and is compared with data of Arena and Mueller [8]

Grahic Jump Location
Fig. 11

Time-averaged streamwise velocity profiles obtained from hotwire measurements for (a) α = 0 deg, (b) α = 5 deg, and (c) α = 10 deg. Inflection layer, where ∂2u¯/∂y2=0, is represented by dashed line.

Grahic Jump Location
Fig. 14

Contours of turbulent kinetic energy in the separated region from PIV measurements for α = 0 deg and 5 deg

Grahic Jump Location
Fig. 15

Normalized shear stress distribution in the separated region from PIV measurements, illustrating the onset of transition for α = 0 deg and 5 deg

Grahic Jump Location
Fig. 16

Time traces of velocity fluctuations u′ along the inflection line of the separated boundary layer for α = 0 deg, 3 deg, 5 deg, and 10 deg

Grahic Jump Location
Fig. 17

Spectra of streamwise velocity fluctuations along the inflection line of the separated boundary layer for α = 0 deg, 3 deg, 5 deg, and 10 deg

Grahic Jump Location
Fig. 18

Amplification of maximum (a) urms and (b) vrms in the streamwise direction illustrating development of the separated boundary layer for α = 0 deg, 3 deg, 5 deg, and 10 deg

Grahic Jump Location
Fig. 12

urms profiles along the model for (a) α = 0 deg, (b) α = 5 deg, and (c) α = 10 deg

Grahic Jump Location
Fig. 13

vrms profiles along the model for (a) α = 0 deg, (b) α = 5 deg, and (c) α = 10 deg

Grahic Jump Location
Fig. 20

Variation of intermittency along the inflection line of the shear layer for α = 0 deg and 5 deg

Grahic Jump Location
Fig. 21

Variations of boundary layer integral parameters for α = 0 deg, 3 deg, 5 deg, and 10 deg (solid symbols represent δ*)

Grahic Jump Location
Fig. 19

Streamwise velocity superimposed with its gradient toillustrate the critical layer for α = 0 deg. Triangle denotes normalized velocity gradient ϕ = (∂u/∂y)/(∂u/∂y)max and square indicates velocity u/U (values within the flow reversal region are deleted).




Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In