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Response of a laminar separation bubble to impulsive forcing

  • Theodoros Michelis (a1), Serhiy Yarusevych (a2) and Marios Kotsonis (a1)

The spatial and temporal response characteristics of a laminar separation bubble to impulsive forcing are investigated by means of time-resolved particle image velocimetry and linear stability theory. A two-dimensional impulsive disturbance is introduced with an alternating current dielectric barrier discharge plasma actuator, exciting pertinent instability modes and ensuring flow development under environmental disturbances. Phase-averaged velocity measurements are employed to analyse the effect of imposed disturbances at different amplitudes on the laminar separation bubble. The impulsive disturbance develops into a wave packet that causes rapid shrinkage of the bubble in both upstream and downstream directions. This is followed by bubble bursting, during which the bubble elongates significantly, while vortex shedding in the aft part ceases. Duration of recovery of the bubble to its unforced state is independent of the forcing amplitude. Quasi-steady linear stability analysis is performed at each individual phase, demonstrating reduction of growth rate and frequency of the most unstable modes with increasing forcing amplitude. Throughout the recovery, amplification rates are directly proportional to the shape factor. This indicates that bursting and flapping mechanisms are driven by altered stability characteristics due to variations in incoming disturbances. The emerging wave packet is characterised in terms of frequency, convective speed and growth rate, with remarkable agreement between linear stability theory predictions and measurements. The wave packet assumes a frequency close to the natural shedding frequency, while its convective speed remains invariant for all forcing amplitudes. The stability of the flow changes only when disturbances interact with the shear layer breakdown and reattachment processes, supporting the notion of a closed feedback loop. The results of this study shed light on the response of laminar separation bubbles to impulsive forcing, providing insight into the attendant changes of flow dynamics and the underlying stability mechanisms.

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M. Alam  & N. D. Sandham 2000 Direct numerical simulation of ‘short’ laminar separation bubble with turbulent reattachment. J. Fluid Mech. 410, 128.

M. Amitay , D. R. Smith , V. Kibens , D. E. Parekh  & A. Glezer 2001 Aerodynamic flow control over an unconventional airfoil using synthetic jet actuators. AIAA J. 39 (3), 361370.

S. Bake , D. G. W. Meyer  & U. Rist 2002 Turbulence mechanism in Klebanoff transition: a quantitative comparison of experiment and direct numerical simulation. J. Fluid Mech. 459, 217243.

N. Benard  & E. Moreau 2014 Electrical and mechanical characteristics of surface AC dielectric barrier discharge plasma actuators applied to airflow control. Exp. Fluids 55 (11), 1846.

A. V. Boiko , G. R. Grek , A. V Dovgal  & V. V. Kozlov 2002 The Origin of Turbulence in Near-Wall Flows. Springer.

M. S. H. Boutilier  & S. Yarusevych 2012 Separated shear layer transition over an airfoil at a low Reynolds number. Phys. Fluids 24, 084105.

L. Brevdo  & T. J. Bridges 1997 Local and global instabilities of spatially developing flows: cautionary examples. Proc. R. Soc. Lond. A 453 (1962), 13451364.

T. C. Corke , C. L. Enloe  & S. P. Wilkinson 2010 Dielectric barrier discharge plasma actuators for flow control. Annu. Rev. Fluid Mech. 42, 505529.

I. Daubechies 1992 Ten Lectures on Wavelets, CBMS-NSF Regional Conference Series in Applied Mathematics, vol. 61. SIAM.

S. S. Diwan  & O. N. Ramesh 2009 On the origin of the inflectional instability of a laminar separation bubble. J. Fluid Mech. 629, 263298.

A. V. Dovgal , V. V. Kozlov  & A. Michalke 1994 Laminar boundary layer separation: instability and associated phenomena. Prog. Aerosp. Sci. 30 (1), 6194.

M. Farge 1992 Wavelet transforms and their applications to turbulence. Annu. Rev. Fluid Mech. 24, 395457.

M. Gaster 1992 Instability, Transition, and Turbulence. Stability of Velocity Profiles with Reverse Flow, pp. 212215. Springer.

M. Gaster  & I. Grant 1975 An experimental investigation of the formation and development of a wave packet in a laminar boundary layer. Proc. R. Soc. Lond. A 347, 253269.

C. P. Häggmark , C. Hildings  & D. S. Henningson 2001 A numerical and experimental study of a transitional separation bubble. Aerosp. Sci. Technol. 5 (5), 317328.

R. Hain , C. J. Kähler  & R. Radespiel 2009 Dynamics of laminar separation bubbles at low-Reynolds-number aerofoils. J. Fluid Mech. 630, 129153.

C. M. Ho  & P. Huerre 1984 Perturbed free shear layers. Annu. Rev. Fluid Mech. 16, 365424.

L. E. Jones , R. D. Sandberg  & N. D. Sandham 2010 Stability and receptivity characteristics of a laminar separation bubble on an aerofoil. J. Fluid Mech. 648, 257296.

C. J. Kähler , S. Scharnowski  & C. Cierpka 2012 On the resolution limit of digital particle image velocimetry. Exp. Fluids 52, 16291639.

C. von Kerczek  & S. H. Davis 1974 Linear stability theory of oscillatory stokes layers. J. Fluid Mech. 62, 753773.

M. Kotsonis 2015 Diagnostics for characterisation of plasma actuators. Meas. Sci. Technol. 26 (9), 092001.

M. Kotsonis , S. Ghaemi , L. L. M. Veldhuis  & F. Scarano 2011 Measurement of the body force field of plasma actuators. J. Phys. D: Appl. Phys. 44 (4), 045204.

J. W. Kurelek , A. R. Lambert  & S. Yarusevych 2016 Coherent structures in the transition process of a laminar separation bubble. AIAA J. 54 (8), 22952309.

D. Lengani , D. Simoni , M. Ubaldi  & P. Zunino 2014 POD analysis of the unsteady behavior of a laminar separation bubble. Exp. Therm. Fluid Sci. 58, 7079.

O. Marxen  & D. S. Henningson 2011 The effect of small-amplitude convective disturbances on the size and bursting of a laminar separation bubble. J. Fluid Mech. 671, 133.

O. Marxen , R. B. Kotapati , R. Mital  & T. Zaki 2015 Stability analysis of separated flows subject to control by zero-net-mass-flux jet. Phys. Fluids 27 (2), 024107.

O. Marxen , M. Lang  & U. Rist 2013 Vortex formation and vortex breakup in a laminar separation bubble. J. Fluid Mech. 728, 5890.

O. Marxen , M. Lang , U. Rist , O. Levin  & D. S. Henningson 2009 Mechanisms for spatial steady three-dimensional disturbance growth in a non-parallel and separating boundary layer. J. Fluid Mech. 634, 165189.

O. Marxen  & U. Rist 2010 Mean flow deformation in a laminar separation bubble: separation and stability characteristics. J. Fluid Mech. 660, 3754.

P. A. Monkewitz  & P. Huerre 1982 The influence of the velocity ratio on the spatial instability of mixing layers. Phys. Fluids 25, 11371143.

L. L. Pauley , P. Moin  & W. C. Reynolds 1990 The structure of two-dimensional separation. J. Fluid Mech. 220, 397411.

R. Pereira , D. Ragni  & M. Kotsonis 2014 Effect of external flow velocity on momentum transfer of dielectric barrier discharge plasma actuators. J. Appl. Phys. 116 (10), 103301.

H. L. Reed , W. S. Saric  & D. Arnal 1996 Linear stability theory applied to boundary layers. Annu. Rev. Fluid Mech. 28, 389428.

W. C. Reynolds  & A. K. M. F. Hussain 1972 The mechanics of an organised wave in turbulent shear flow. Part 3. Theoretical models and comparisons with experiments. J. Fluid Mech. 54, 263288.

U. Rist  & K. Augustin 2006 Control of laminar separation bubbles using instability waves. AIAA J. 44 (10), 22172223.

U. Rist  & U. Maucher 2002 Investigations of time-growing instabilities in laminar separation bubbles. Eur. J. Mech. (B/Fluids) 21 (5), 495509.

N. D. Sandham 2008 Transitional separation bubbles and unsteady aspects of aerofoil stall. Aeronaut. J. 112, 395404.

F. Scarano  & M. L. Riethmuller 2000 Advances in iterative multigrid PIV image processing. Exp. Fluids 29 (SUPPL. 1), S51S60.

J. Serna  & B. J. Lázaro 2014 The final stages of transition and the reattachment region in transitional separation bubbles. Exp. Fluids 55 (4), 1695.

J. Serna  & B. J. Lázaro 2015 On the bursting condition for transitional separation bubbles. Aerosp. Sci. Technol. 44, 4350.

D. Simoni , M. Ubaldi , P. Zunino  & F. Bertini 2012a Transition mechanisms in laminar separation bubbles with and without incoming wakes and synthetic jets. Exp. Fluids 53, 173186.

D. Simoni , M. Ubaldi , P. Zunino , D. Lengani  & F. Bertini 2012b An experimental investigation of the separated-flow transition under high-lift turbine blade pressure gradients. Flow Turbul. Combust. 88, 4562.

L. Sirovich 1987 Turbulence and the dynamics of coherent structures. I – Coherent structures. II – Symmetries and transformations. III – Dynamics and scaling. Q. Appl. Maths 45, 561571; 573–590.

I. Tani 1964 Low-speed flows involving bubble separations. Prog. Aerosp. Sci. 5, 70103.

V. Theofilis 2011 Global linear instability. Annu. Rev. Fluid Mech. 43, 319352.

V. Theofilis , S. Hein  & U. Dallmann 2000 On the origins of unsteadiness and three-dimensionality in a laminar separation bubble. Phil. Trans. R. Soc. Lond. A 358 (1777), 32293246.

J. H. Watmuff 1999 Evolution of a wave packet into vortex loops in a laminar separation bubble. J. Fluid Mech. 397, 119169.

P. Welch 1967 The use of fast Fourier transform for the estimation of power spectra: a method based on time averaging over short, modified periodograms. IEEE Trans. Audio Electroacoust. 15, 7073.

B. Wieneke 2015 PIV uncertainty quantification from correlation statistics. Meas. Sci. Technol. 26 (7), 074002.

Z. Yang  & P. R. Voke 2001 Large-eddy simulation of boundary-layer separation and transition at a change of surface curvature. J. Fluid Mech. 439, 305333.

S. Yarusevych  & M. Kotsonis 2017 Effect of local DBD plasma actuation on transition in a laminar separation bubble. Flow Turbul. Combust. 98, 195216.

S. Yarusevych , P. E. Sullivan  & J. G. Kawall 2007 Effect of acoustic excitation amplitude on airfoil boundary layer and wake development. AIAA J. 45 (4), 760771.

K. B. M. Q. Zaman , D. J. McKinzie  & C. L. Rumsey 1989 Natural low-frequency oscillation of the flow over an airfoil near stalling conditions. J. Fluid Mech. 202, 403442.

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Michelis et al. supplementary movie
Phase-averaged vorticity within the forcing cycle

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