Effects of freestream turbulence on the wakes of circular and square cylinders

Abstract

Two cylinder geometries, circular and square, were subjected to four distinct inflows to investigate the effects of freestream turbulence (FST) on their wake development. The wake flow fields were measured using planar particle image velocimetry with a large field of view, covering a contiguous area up to 20 cylinder diameters (D) downstream of the wake-generating body. The experiments were conducted at a Reynolds number of ReD = 33 000. The turbulent inflows were generated using an active grid, which produced freestream turbulence intensities ranging from 1.1% to 13.8%. The integral scales of the turbulence varied between 4.32D and 7.86D. The findings demonstrate that FST facilitates the recovery of the wake velocity deficit and promotes an earlier trend towards self-similarity in the velocity profile. Moreover, a reduction in the coherence of the shed vortices is observed in the wake as FST increases, resulting in a lower average number of coherent shed vortices and a transfer of energy from the proper orthogonal decomposition modes associated with vortex shedding to modes associated with the background turbulence. These observations explicitly demonstrate that the enhanced mixing due to elevated freestream turbulence facilitates faster wake recovery, loss of coherence of the shed vortices, approach to self-similarity of velocity statistics, and significant alterations in the instantaneous wake flow field.