Hostname: page-component-cd9895bd7-jkksz Total loading time: 0 Render date: 2024-12-28T07:03:51.788Z Has data issue: false hasContentIssue false
  • English
  • Français

The flow over a backward-facing step under controlled perturbation: laminar separation

Published online by Cambridge University Press:  26 April 2006

M. A. Z. Hasan
M. A. Z. Hasan
Affiliation:
Mechanical Engineering Department, King Fahd University of Petroleum & Minerals. Dhahran 31261, Saudi Arabia
Get access Rights & Permissions [Opens in a new window]

Abstract

The flow over a backward-facing step with laminar separation was investigated experimentally under controlled perturbation for a Reynolds number of 11000, based on a step height h and a free-stream velocity UO. The reattaching shear layer was found to have two distinct modes of instability: the ‘shear layer mode’ of instability at Stθ ≈ 0.012 (Stθ ≡ fθ/UO, θ being the momentum thickness at separation and f the natural roll-up frequency of the shear layer); and the ‘step mode’ of instability at Sth ≈ 0.185 (Sth ≡ fh/U0). The shear layer instability frequency reduced to the step mode one via one or more stages of a vortex merging process. The perturbation increased the shear layer growth rate and the turbulence intensity and decreased the reattachment length compared to the unperturbed flow. Cross-stream measurements of the amplitudes of the perturbed frequency and its harmonics suggested the splitting of the shear layer. Flow visualization confirmed the shear layer splitting and showed the existence of a low-frequency flapping of the shear layer.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 238 , May 1992 , pp. 73 - 96
Copyright
© 1992 Cambridge University Press

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Baker, S. 1977 Regions of recirculating flow associated with two-dimensional steps. Ph.D. thesis, Dept. of Civil Engng, University of Surrey.
Bhattacharjee, S., Scheelke, B. & Troutt, T. R. 1986 Modification of vortex interactions in a reattaching separated flow. AIAA J. 24, 623.Google Scholar
Bradshaw, P. & Wong, F. Y. F. 1972 The reattachment and relaxation of a turbulent shear layer. J. Fluid Mech. 52, 113.Google Scholar
Browand, F. K. 1966 An experimental investigation of the instability of an incompressible separated shear layer. J. Fluid Mech. 26, 281.Google Scholar
Brown, G. & Roshko, A. 1974 On density effects and large structure in a turbulent mixing layer. J. Fluid Mech. 64, 775.Google Scholar
Castro, I. P. 1981 Measurements in shear layers separating from surface mounted obstacles. J. Wind Engng Indust. Aero. 7, 253.Google Scholar
Castro, I. P. & Haque, A. 1987 The structure of a turbulent shear layer bounding a separation region. J. Fluid Mech. 179, 439.Google Scholar
Castro, I. P. & Haque, A. 1988 The structure of a turbulent shear layer bounding a separation region. Part 2. Effects of free-stream turbulence. J. Fluid Mech. 192, 577.Google Scholar
Chandrsuda, C. 1975 A reattaching turbulent shear layer in incompressible flow. Ph.D. thesis, Dept. of Aeronautics, Imperial College of Science & Technology.
Cherry, N. J., Hillier, R. & Latour, M. E. M. P. 1984 Unsteady measurements in a separated and reattaching flow. J. Fluid Mech. 144, 13.Google Scholar
Crow, S. C. & Champagne, F. H. 1971 Orderly structure in jet turbulence. J. Fluid Mech. 48, 547.Google Scholar
Eaton, J. K. & Johnston, J. P. 1980 Turbulent flow reattachment: An experimental study of the flow and structure behind a backward-facing step. Rep. MD-39. Dept. of Mech. Engn., Stanford University.Google Scholar
Eaton, J. K. & Johnston, J. P. 1981 A review of research on subsonic turbulent flow reattachment. AIAA J. 19, 1093.Google Scholar
Freymuth, P. 1966 On transition in a separated laminar boundary layer. J. Fluid Mech. 25, 683.Google Scholar
Goldstein, M. E. & Hultgren, L. S. 1988 Nonlinear spatial evolution of an externally excited instability wave in a free shear layer. J. Fluid Mech. 197, 295.Google Scholar
Hasan, M. A. Z. 1983 The effects of external and self excitations on axisymmetric jet turbulence and noise. Ph.D. thesis, University of Houston.
Ho, C. M. & Huang, L. S. 1982 Subharmonic and vortex merging in mixing layers. J. Fluid Mech. 119, 443.Google Scholar
Husain, Z. D. & Hussain, A. K. M. F. 1983 Natural instability of free shear layers. AIAA J. 21, 1512.Google Scholar
Hussain, A. K. M. F. & Hasan, M. A. Z. 1983 The whistler nozzle phenomenon. J. Fluid Mech. 134, 431.Google Scholar
Hussain, A. K. M. F. & Hasan, M. A. Z. 1985 Turbulence suppression in free turbulent shear flow under controlled excitation. Part 2. Jet-noise reduction. J. Fluid Mech. 150, 159.Google Scholar
Hussain, A. K. M. F. & Zaman, K. B. M. Q. 1981 The preferred mode of the axisymmetric jet. J. Fluid Mech. 110, 39.Google Scholar
Jaroch, M. P. & Fernholz, H. H. 1989 The three-dimensional character of a nominally twodimensional separated turbulent shear flow. J. Fluid Mech. 205, 523.Google Scholar
Kelly, R. E. 1967 On the stability of an inviscid shear layer which is periodic in space and time. J. Fluid Mech. 27, 657.Google Scholar
Khan, A. S. 1990 An experimental study of reattaching flow over a backward facing step with controlled perturbation. MS thesis, Mech. Engng. Dept., KFUPM, Dhahran, Saudi Arabia.
Kibens, V. 1980 Discrete noise spectrum generated by an acoustically excited jet. AIAA J. 18, 434.Google Scholar
Kim, J., Kline, S. J. & Johnston, J. P. 1978 Investigation of separation and reattachment of a turbulent shear layer: Flow over a backward-facing step. Rep. MD-37. Thermoscience Div., Dept. of Mech. Engng, Stanford University.Google Scholar
Kiya, M. & Sasaki, K. 1983 Structure of a turbulent separation bubble. J. Fluid Mech. 137, 83.Google Scholar
Mattingly, G. E. & Criminals, W. O. 1972 The stability of an incompressible two-dimensional wake. J. Fluid Mech. 51, 233.Google Scholar
McGuinness, M. 1978 Flow with separation bubble-steady and unsteady aspects. Ph.D. dissertation, Cambridge University.
Michalke, A. 1965 On spatially growing disturbances in an inviscid shear layer. J. Fluid Mech. 22, 371.Google Scholar
Miksad, R. W. 1972 Experiments on the nonlinear stages of free-shear-layer transition. J. Fluid Mech. 56, 695.Google Scholar
Pfizenmaier E. 1973 On the instability of a sound influenced free jet. Inst. für Turbulenzforach, Berlin.
Pronchick, S. W. & Kline, S. J. 1983 An experimental investigation of the structure of a turbulent reattaching flow behind a backward facing step Rep. MD-42. Thermosciences Division, Dept. of Mech. Engng. Stanford University.Google Scholar
Roos, F. W. & Kegelman, J. T. 1986 Control of coherent structures in reattaching laminar and turbulent shear layers. AIAA J. 24, 1956.Google Scholar
Roshko, A. & Lau, J. C. 1965 Some observations on transition and reattachment of a free shear layer in incompressible flow. In Proc. 1965 Heat Transfer and Fluid Mech. Inst.; Stanford University.
Rothe, P. H. & Johnston, J. P. 1979 Free-shear-layer behaviour in rotating systems. Trans. Asme I: J. Fluids Engng, 101, 117.Google Scholar
Ruderich, R. & Fernholz, H. H. 1986 An experimental investigation of a turbulent shear flow with separation, reverse flow, and reattachment. J. Fluid Mech. 163, 283.Google Scholar
Sato, H. 1960 The stability and transition of a two-dimensional jet. J. Fluid Mech. 7, 53.Google Scholar
Troutt, T. R., Scheelke, B. & Norman, T. R. 1984 Organized structure in a reattaching separated flow field. J. Fluid Mech. 143, 413.Google Scholar
Winant, C. D. & Browand, F. K. 1974 Vortex pairing: the mechanism of turbulent mixing-layer growth at moderate Reynolds number. J. Fluid Mech. 63, 237.Google Scholar
Zaman, K. B. M. Q. & Hussain, A. K. M. F. 1980 Vortex pairing on a circular jet under controlled excitation. Part 1. General jet response. J. Fluid Mech. 101, 449.Google Scholar
Zaman, K. B. M. Q. & Hussain, A. K. M. F. 1981 Turbulence suppression in free turbulent shear flow under controlled excitation. J. Mech. 103, 133.Google Scholar