Stability of impulsively started vortex rolls

Curtis Hamman, Stanford University

Large helical vortex rolls with axes in the general direction of the mean wind appear quite often in the unstably stratified atmospheric boundary layer. When a rapid shift in the mean wind direction occurs, however, this orderly pattern of counter-rotating longitudinal rolls is destroyed and replaced by a non-equilibrium turbulent flow that, through a complex sequence of structural changes, may eventually develop back into a stable roll pattern, aligned with the new wind direction. This transition process is studied via direct numerical simulation of plane channel flow heated from below with impulsively started transverse pressure gradient.

Abstract Author(s): Curtis W. Hamman and Parviz Moin