Abstract
Subharmonic-perturbed shear flow downstream of a two-dimensional backward-facing step was experimentally investigated. The Reynolds number was Reh = 2.0 ×104, based on free-stream velocity and step height. Planar 2D-2C particle image velocimetry was employed to measure the separating and reattaching flow in the horizontal-vertical plane in the center position. The subharmonic perturbations were generated by an oscillating flap which was implemented over the step edge and driven by periodic Ampere force. The subharmonic frequency was 55 Hz as the half of the fundamental frequency of the turbulent shear layer. As a result of the subharmonic perturbations, the size of recirculation region behind the backward-facing step is reduced and the time-averaged reattachment length is 31.0% shorter than that of the natural flow. The evolution of vortices, including vortex roll-up, growth and breakdown process, is analyzed by using phase-averaging, cross-correlation function and proper orthogonal decomposition. It is found that Reynolds shear stress is considerably increased in which the vortices roll up and then break down further downstream. In particular, rapid growth of vortices based on the “step mode” occurs at approximate half of the recirculation region, caused by in interaction between the shear layer and the recirculation region. Furthermore, the coherent structures, which are represented by a phase-correlated POD mode pair, are reconstructed in phases in order to show regular patterns of the subharmonic-perturbed coherent structures.
Similar content being viewed by others
References
Eaton, J.K., Johnston, J.P.: A review of research on subsonic turbulent-flow reattachment. AIAA J. 19, 1093–1100 (1981)
Bhattacharjee, S., Scheelke, B., Troutt, T.R.: Modification of vortex interactions in a reattaching separated flow. AIAA J. 24(4), 623–629 (1986)
Hasan, M.A.Z.: The flow over a backward-facing step under controlled perturbation: laminar separation. J. Fluid Mech. 238, 73–96 (1992)
Chun, K.B., Sung, H.J.: Control of turbulent separated flow over a backward-facing step by local forcing. Exp. Fluids 21, 417–426 (1996)
Wengle, H., Huppertz, A., Bärwolff, G., Janke, G.: The manipulated transitional backward-facing step flow: an experimental and direct numerical simulation investigation. Eur. J. Mech. B-Fluids 20, 25–46 (2001)
Smits, A.J.: A Visual Study of a Separation Bubble Proceeding of the 2Nd International Symposium on Flow Visualization, Germany (1980)
Hudy, L.M., Naguib, A., Humphreys, W.M.: Stochastic estimation of a separated-flow field using wall-pressure-array measurements. Phys. Fluids 19, 024103 (2007)
Huerre, P., Monkewitz, P.A.: Absolute and convective instabilities in free shear layers. J. Fluid Mech. 159, 151–168 (1985)
Sigurdson, L.W.: The structure and control of a turbulent reattaching flow. J. Fluid Mech. 298, 139–165 (1995)
Roos, F.W., Kegelman, J.T.: Control of coherent structures in reattaching laminar and turbulent shear layers. AIAA J. 24, 1956–1963 (1986)
Ma, X., Geisler, R., Agocs, J., Schröder, A.: Investigation of coherent structures generated by acoustic tube in turbulent flow separation control. Exp. Fluids 56, 46 (2015)
Ma, X., Geisler, R., Schröder, A.: Experimental investigation of three-dimensional vortex structures downstream of vortex generators over a backward-facing step. Flow Turbulence Combust 98, 389–415 (2017)
Sujar-Garrido, P., Benard, N., Moreau, E., Bonnet, J.P.: Dielectric barrier discharge plasma actuator to control turbulent flow downstream of a backward-facing step. Exp. Fluid 56, 70 (2015)
Benard, N., Sujar-Garrido, P., Bonnet, J., Moreau, E.: Control of the coherent structures dynamics downstream of a backward-facing step by DBD plasma actuator. Int. J. Heat Fluid Fl. 61, 158–173 (2016)
Kelly, R.E.: On the stability of an inviscid shear layer which is periodic in space and time. J. Fluid Mech. 27, 657–689 (1967)
Zaman, K.B.M.Q., Hussain, A.K.M.F.: Vortex pairing in a circular jet under controlled excitation. Part 1. General jet response. J. Fluid Mech. 101(3), 449–491 (1980)
Oster, D., Wygnanski, I.: The forced mixing layer between parallel streams. J. Fluid Mech. 123, 91–130 (1982)
Ho, C.M., Huang, L.S.: Subharmonic and vortex merging in mixing layers. J. Fluid Mech. 119, 443–473 (1982)
Chao, Y.C., Han, J.M., Jeng, M.S.: A quantitative laser sheet image processing method for the study of the coherent structure of a circular jet flow. Exp. Fluids 9, 323–332 (1990)
Husain, H.S., Hussain, A.K.M.F.: Experiments on subharmonic resonance in a shear layer. J. Fluid Mech. 304, 343–372 (1995)
Kostas, J., Soria, J., Chong, M.S.: Particle image velocimetry measurements of a backward-facing step flow. Exp. Fluids 33, 838–853 (2002)
Dejoan, A., Leschziner, M.A.: Large eddy simulation of periodically perturbed separated flow over a backward-facing step. Int. J. Heat Fluid Fl. 25, 581–592 (2004)
De Brederode, V., Bradshaw, P.: Influence of the side walls on the turbulent center-plane boundary layer in a square duct. J. Fluids Eng. 100, 91–96 (1978)
Kähler, C. J., Sammler, B., Kompenhans, J.: Generation and control of tracer particles for optical flow investigations in air. Exp. Fluids 33, 736–742 (2002)
Raffel, M., Willert, C.E., Wereley, S.T., Kompenhans, J.: Particle Image Velocimetry: a Practicle Guide. Springer Press, Berlin (2007)
Willert, C.E., Gharib, M.: Digital particle image velocimetry. Exp. Fluids 10, 181–193 (1991)
Taylor, G.I.: Statistical theory of turbulence. Proc. R. Soc. Lond. A 151, 421–444 (1935)
Taylor, G.I.: Correlation measurements in a turbulent flow through a pipe. Proc. R. Soc. Lond. A 157, 537–546 (1936)
Favre, A.J., Gaviglio, J.J., Dumas, R.: Space-time double correlations and spectra in a turbulent boundary layer. J. Fluid Mech. 2(4), 313–342 (1957)
Favre, A.J., Gaviglio, J.J., Dumas, R.: Structure of velocity space time correlations in a boundary layer. Phys. Fluids 10, S138 (1967)
Schlichting, H.: Boundary-Layer Theory. McGRAW-HILL Press, New York (1979)
Hussain, A.K.M.F., Reynolds, W.C.: The mechanics of an organized wave in turbulent shear layer. J. Fluid Mech. 41(2), 241–258 (1970)
Scarano, F., Riethmuller, M.L.: Iterative multigrid approach in PIV image processing with discrete window offset. Exp. Fluids 26, 513–523 (1999)
Eaton, J.K., Johnston, J.P.: Low frequency unsteadyness of a reattaching turbulent shear layer. Turbulent Shear Flow 3. Springer-Verlag, Berlin Heidelberg (1982)
Driver, D.M., Seegmiller, H.L., Marvin, J.: Time-dependent behavior of a reattaching shear layer. AIAA J. 25, 914–919 (1987)
Hussain, A.K.M.F.: Coherent structures and turbulence. J. Fluid Mech. 173, 303–356 (1986)
Lumley, J.L.: The Structure of Inhomogeneous Turbulent Flow Proceeding of the Atmospheric Turbulence and Radio Wave Propagation, Moscow (1967)
Sirovich, L.: Turbulence and the dynamics of coherent structures. Part 1: coherent structure. Q. Appl. Math. 45(3), 561–571 (1987)
Meyer, K.E., Pedersen, J.M., Özcan, O.: A turbulent jet in crossflow analysed with proper orthogonal decomposition. J. Fluid Mech. 583, 199–227 (2007)
Perrin, R., Braza, M., Cid, E., Cazin, S., Barthet, A., Sevrain, A., Mockett, C., Thiele, F.: Obtaining phase averaged turbulence properties in the near wake of a circular cylinder at high Reynolds number using POD. Exp. Fluids 43, 341–355 (2007)
Schmid, P.J., Violato, D., Scarano, F.: Decomposition of time-resolved tomographic PIV. Exp. Fluids 52, 1567–1579 (2012)
Acknowledgments
The authors sincerely thank Dr. Daniel Schanz and Mr. Janos Agocs from the German Aerospace Center for valuable discussion and essential support during the wind tunnel test.
Author information
Authors and Affiliations
Corresponding author
Ethics declarations
Conflict of interests
The authors declare that they have no conflict of interest.
Rights and permissions
About this article
Cite this article
Ma, X., Geisler, R. & Schröder, A. Experimental Investigation of Separated Shear Flow under Subharmonic Perturbations over a Backward-Facing Step. Flow Turbulence Combust 99, 71–91 (2017). https://doi.org/10.1007/s10494-017-9814-1
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s10494-017-9814-1