Distribution of spanwise enstrophy in the near wake of three symmetric elongated bluff bodies at high Reynolds number

Abstract

Three elongated bluff bodies with a chord-to-thickness ratio of seven have been studied experimentally at a Reynolds number based on body thickness of 3 × 104. The defining feature of elongated bluff bodies is the interaction between trailing edge Kármán vortex shedding and leading edge separation-reattachment. We have used particle image velocimetry with different body geometries to investigate this interaction for three distinct cases: (i) small leading edge separation-reattachment length; (ii) large leading edge separation-reattachment length; and (iii) one case in between these bounds. The leading edge separation-reattachment is a significant source of spanwise enstrophy. Thus, changes in the wake enstrophy distribution are of particular interest. We have examined the time-averaged distribution and production of both the turbulent kinetic energy and the spanwise enstrophy in the near wake region utilizing proper orthogonal decomposition on the vorticity field to distinguish between turbulence and the periodic contribution of the trailing edge vortex shedding. A significant increase in the lateral distribution of spanwise enstrophy is observed – exceeding the typical bounds of the near wake – which is due to the leading edge separation-reattachment and the resulting scale of the flow at the trailing edge. As a result, strengthening the leading edge flow, which tends to weaken the trailing edge vortex shedding, may lead to enhanced mixing in the wake.