On the structure of a turbulent spot in a heated laminar boundary layer
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An artificially generated turbulent spot was investigated experimentally in a heated boundary layer using a rake of mini-thermocouples. Simultaneous temperature traces were used to determine the spot's leading and trailing edge characteristics. The measurements on the centerline of the plate at a constant velocity and variable streamwise positions provided a Re x range of 2.45–12.6 x 105. At one axial station the free stream velocity was varied and off-axis measurements were obtained.
The shape of the interface between the spot and the surrounding laminar flow was described by conventional and conditional histograms. The length of the spot's leading edge (i.e. the “overhang”) increased linearly with the downstream distance. Off-axis, the length of the overhang decreased slightly towards the “wing tips” but became larger with respect to the spot's streamwise extent. The trailing edge changed less significantly in the downstream direction.
It was shown that when two spots are generated such that the leading edge of the upstream spot is in the calmed region of the downstream spot, the celerity of the upstream spot is decreased and the spots ultimately merge.
KeywordsBoundary Layer Free Stream Free Stream Velocity Laminar Boundary Layer Downstream Direction
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- Amini, J. 1978: Controlée en couche limité: Etude expérimental du développement d'une perturbation tridimensionelle instantanée. Ph.D. Thesis, Institut de Mécanique de GrenobleGoogle Scholar
- Antonia, R. A.; Chambers, A. J.; Sokolov, M.; Van Atta, C. W. 1981: Simultaneous temperature and velocity measurements in the plane of symmetry of a transitional turbulent spot. J. Fluid Mech. 108, 317–343Google Scholar
- Blackwelder, R. F.; Chang, S. I. 1986: in preparationGoogle Scholar
- Cantwell, B.; Coles, D.; Dimotakis, P. 1978: Structure and entrainment in the plane of symmetry of a turbulent spot. J. Fluid Mech. 87, 641–672Google Scholar
- Carlson, D. R.; Widnall, S. E.; Peeters, M. F. 1982: A flow-visualization study of transition in plane Poiseuille flow. J. Fluid Mech. 121, 487–505Google Scholar
- Charters, A. C. 1943: Transition between laminar and turbulent flow by transverse contamination. N.A.C.A. Tech. Note No. 891Google Scholar
- Emmons, H. W. 1951: The laminar-turbulent transition in a boundary layer. J. Aero. Sci. 18, 490–498Google Scholar
- Gad-el-Hak, M.; Blackwelder, R. F.; Riley, J. J. 1981: On the growth of turbulent regions in laminar boundary layers. J. Fluid Mech. 110, 73Google Scholar
- Lindberg, P.-A.; Fahlgren, M. E.; Alfredsson, P. H.; Johansson, A. V. 1985: An experimental study of the structure and spreading of turbulent spots. In: 2nd Symp. on Laminar Turbulent Transition (ed. Kozlov, V. B.), p. 617. Berlin, Heidelberg, New York: SpringerGoogle Scholar
- Matsui, T. 1980: Visualization of turbulent spots in the boundary layer. In: IUTAM Symp. on Laminar-Turbulent Transition (eds. Eppler, R.; Fasel, H.), p. 288. Berlin, Heidelberg, New York: SpringerGoogle Scholar
- Mautner, T. S.; Van Atta, C. W. 1982: An experimental study of the wall-pressure field associated with a turbulent spot in a laminar boundary layer. J. Fluid Mech. 118, 59–77Google Scholar
- Motohashi, T.; Blackwelder, R. F. 1983: Decreasing the side wall contamination in wind tunnels. J. Fluids Eng. 105, 435–438Google Scholar
- Schubauer, G. B.; Klebanoff, P. S. 1955: Contributions on the mechanics of boundary layer transition. NACA TN 3489 (also NACA TN 1289), pp. 299–315Google Scholar
- Schubauer, G. B.; Skramstad, H. K. 1948: Laminar boundary layer oscillations and transition on a flat plate. NACA Rept. 909Google Scholar
- Van Atta, C. W.; Helland, K. N. 1980: Temperature tagging measurements of turbulent spots in a heated laminar boundary layer. In: Laminar-Turbulent Transition (eds. Eppler, R.; Fasel, H.), pp. 311–320. Berlin, Heidelberg, New York: SpringerGoogle Scholar
- Wygnanski, I.; Sokolov, M.; Friedman, D. 1976: On a turbulent spot in a laminar boundary layer. J. Fluid Mech. 78, 785–819Google Scholar
- Wygnanski, I.; Zilberman, M.; Haritonidis, J. 1982: On the spreading of a turbulent spot in the absence of a pressure gradient. J. Fluid Mech. 123, 69–90Google Scholar
- Zilberman, M. 1981: On the interaction of transition spots and generation of a synthetic turbulent boundary layer. Ph.D. Thesis, Tel-Aviv University, IsraelGoogle Scholar