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Structure of a turbulent separation bubble

  • Masaru Kiya (a1) and Kyuro Sasaki (a1)

Abstract

Flow in the separation bubble formed along the sides of a blunt flat plate with right-angled corners has been studied in terms of extensive single- and two-point measurements of velocity and surface-pressure fluctuations. The cross-correlations between the surface-pressure and velocity fluctuations are found to be useful for the study of large-scale vortex structure in the bubble. Large-scale vortices are shed downstream from the separation bubble with a frequency of about 0.6U/xR, where U is the approaching velocity and xR is the time-mean length of the bubble. On top of this regular vortex shedding, there exists a large-scale unsteadiness in the bubble. Vortices which are much larger than the regular vortices are shed with frequencies less than about 0.2U/xR. The large-scale unsteadiness is accompanied by enlargement and shrinkage of the bubble and also by a flapping motion of the shear layer near the separation line. The intermittent nature of the flow in the bubble is clarified in some detail. The distributions of the cross-correlations between the pressure and velocity fluctuations demonstrate the vortex structure in the reattaching zone. The longitudinal distance between the vortices is estimated to be (0.7–0.8) xR and their convection velocity is about 0.5U near the reattachment line. The cross-correlations also suggest the existence of a longitudinal counter-rotating system in the bubble. The distance between the axes of the rotation is of the order of 0.6xR. Variations of timescales, lengthscales and phase velocities of the vortices are presented and discussed.

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References

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Antonia, R. A. & van Atta, C. W. 1977 Statistical characteristics of Reynolds stresses in a turbulent boundary layer AIAA J. 15, 7175.
Bradshaw, P. 1967 Irrotational fluctuations near a turbulent boundary layer J. Fluid Mech. 27, 209230.
Bradshaw, P. & Wong, F. Y. F. 1972 The reattachment and relaxation of a turbulent shear layer J. Fluid Mech. 52, 113135.
Chandrsuda, C. & Bradshaw, P. 1981 Turbulence structure of a reattaching mixing layer J. Fluid Mech. 110, 171194.
Eaton, J. K. & Johnston, J. P. 1982 Low frequency unsteadiness of a reattaching turbulent shear layer. In Turbulent Shear Flows 3 (ed. L. J. S. Bradbury, F. Durst, B. E. Launder, F. W. Schmidt & J. H. Whitelaw), pp. 162170. Springer.
Fernholz, H. H. 1978 External flows. In Turbulence, 2nd edn (ed. P. Bradshaw), p. 45. Springer.
Fiedler, H. & Head, M. R. 1966 Intermittency measurements in the turbulent boundary layer J. Fluid Mech. 25, 719735.
Hillier, R. & Cherry, N. J. 1981a Pressure fluctuations under a turbulent shear layer. In Proc. 3rd Turbulent Shear Flow Symp., Davis, California, 9810 September, pp. 16.23810.28.
Hillier, R. & Cherry, N. J. 1981b The effects of stream turbulence on separation bubbles J. Wind Engng & Ind. Aerodyn. 8, 4958.
Johnston, J. P. 1978 Internal flows. In Turbulence, 2nd edn (ed. P. Bradshaw), p. 109. Springer.
Kiya, M., Sasaki, K. & Arie, M. 1982 Discrete-vortex simulation of a turbulent separation bubble J. Fluid Mech. 120, 219244.
Komatsu, S. & Kobayashi, H. 1980 Vortex-induced oscillation of bluff cylinder J. Wind Engng & Ind. Aerodyn. 6, 335362.
Lane, J. C. & Loehrke, R. I. 1980 Leading edge separation from a blunt plate at low Reynolds number. Trans. ASME I: J. Fluids Engng 102, 494810.
Ota, T., Asano, Y. & Okawa, J. 1981 Reattachment length and transition of the separated flow over blunt flat plates Bull. JSME 24, 941947.
Ota, T. & Itasaka, M. 1976 A separated and reattached flow over a blunt flat plate. Trans. ASME I: J. Fluid Engng 98, 79810.
Ota, T. & Narita, M. 1978 Turbulence measurements in a separated and reattached flow over a blunt flat plate. Trans. ASME I: J. Fluids Engng 100, 224810.
Willmarth, W. W. & Wooldridge, C. E. 1963 Measurements of the correlation between the fluctuating velocities and the fluctuating wall pressure in a thick turbulent boundary layer. AGARD Rep. 456.
Wood, D. H. & Bradshaw, P. 1982 A turbulent mixing layer constrained by a solid surface. Part 1. Measurements before reaching the surface J. Fluid Mech. 122, 5789.
Wygnanski, I. & Fiedler, H. E. 1970 The two-dimensional mixing layer J. Fluid Mech. 41, 327361.
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Journal of Fluid Mechanics
  • ISSN: 0022-1120
  • EISSN: 1469-7645
  • URL: /core/journals/journal-of-fluid-mechanics
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