The Peculiar Behavior of Stationary and Accelerating Vortices

Featuring Robert E. Breidenthal, Ph.D.
Professor, Aeronautics and Astronautics
University of Washinghton
 
Location: McDonell Douglas Engineering Auditorium
Free and open to the public

Abstract:
Experiments have revealed that the fluxes at a surface near a vortex depend strongly on the stationarity of the vortex in a counter- intuitive way.  One example is a vertical jet impinging on a stratified interface.  The entrainment rate across the interface drops by orders of magnitude if the jet is tilted slightly and precessed.  Another example is the addition of strong, streamwise vortices to a turbulent boundary layer.  If the plate is flat so that the vortices are unstable and wiggle around, the wall fluxes increase.  However, if the plate is corrugated so that the vortices are stationary, the boundary layer is largely relaminarized.  A seemingly unrelated topic is accelerating vortices, in which the rotation rate rapidly increases in time.  A new class of self- similar, turbulent flows is proposed in which acceleration changes the dimensionless entrainment rate.  For all flows except Rayleigh-Taylor, acceleration inhibits entrainment. A connection between stationary and rapidly accelerating vortices is proposed.