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Statistical structure of momentum sources and sinks in the outer region of a turbulent boundary layer

Published online by Cambridge University Press:  10 July 2008

B. GANAPATHISUBRAMANI
B. GANAPATHISUBRAMANI*
Affiliation:
Department of Aeronautics, Imperial College London, Prince Consort Road, South Kensington, London, SW7 2AZ, [email protected]
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Abstract

The spatial structure of momentum sources and sinks (T > 0 and T < 0; where T is the streamwise component of the Lamb vector) is examined in a turbulent boundary layer by using dual-plane particle image velocimetry data obtained in streamwise–spanwise planes at two wall-normal locations (x2/δ = 0.1 and 0.5, where x2 is the wall-normal location and δ is the boundary layer thickness). Two-point correlations of T indicate that the size of source motions remains relatively constant while the size of sink motions increases with increasing wall-normal distance. The relative strength of sink motions also increases away from the wall. The velocity field in the vicinity of source/sink motions was explored by computing cross-correlations of T with the velocity components. Source-like motions are correlated with elongated low-momentum zones that possess regions of upwash embedded within them and appear to be the strongest in areas where these low-momentum zones meander in the spanwise direction. Momentum sinks appear to be located within low-speed regions that are within larger high-momentum zones. The velocity fluctuations undergo rapid transitions between quadrants in the vicinity of sinks (i.e. both streamwise and wall-normal velocity fluctuations change sign). The length scales, over which the fluctuations change sign, are much larger at x2/δ = 0.5 than at x2/δ = 0.1.

Type
Papers
Information
Journal of Fluid Mechanics , Volume 606 , 10 July 2008 , pp. 225 - 237
Copyright
Copyright © Cambridge University Press 2008

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