Prof. Robert Breidenthal: The peculiar behavior of stationary and accelerating vortices in fluids

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Povzetek:

    The peculiar behavior of stationary and accelerating vortices in fluids

    Prof. Robert Breidenthal*, University of Washington, Seattle, USA

Laboratory experiments reveal that the entrainment rate of vortices is dramatically altered when the vortices are stationary or accelerating.  In the forced shear layer of Oster and Wygnanski, the entrainment rate vanishes when the vortices are stationary, corresponding to Kelvin's cats eye flow.  Stationary, streamwise vortices in initially turbulent boundary layers partially relaminarize the flow. The entrainment rate across the interface decreases by orders of magnitude if jet is instead tilted slightly.  This is attributed to the transition from stationary to nonstationary regimes.  Acceleration of vortices, whereby their rotation period is constant or decreases in time, is also known to reduce entrainment.  A general theory has been proposed to account for acceleration. 

*http://www.aa.washington.edu/faculty/breidenthal/