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Statistical structure of momentum sources and sinks in the outer region of a turbulent boundary layer. (English) Zbl 1178.76017
Summary: 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 (\(x_{2}/\delta = 0.1\) and \(0.5\), where \(x_{2}\) is the wall-normal location and \(\delta \) 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 \(x_{2}/\delta = 0.5\) than at \(x_{2}/\delta = 0.1\).

MSC:
76-05 Experimental work for problems pertaining to fluid mechanics
76F40 Turbulent boundary layers
76F55 Statistical turbulence modeling
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