On the wake with and without vortex shedding suppression behind a two-dimensional square cylinder in proximity to a plane wall

A comparative study of the wake characteristics behind a two-dimensional square cylinder in proximity to a plane wall was made on two systems, i.e. G/D=0.25 and 0.5, which corresponds to the wakes with and without suppression of the vortex shedding, respectively. Here, G is the gap distance and D is the width of the square cylinder. Synchronized measurements of wall-pressure fluctuations and velocity fluctuations were made using a microphone array and a split-fiber film, respectively. For the system G/D=0.5, a regular Karman-like vortex shedding at fD/U0=0.13 was found by inspection of the streamwise velocity spectra. When the gap width is reduced to G/D=0.25, a low-speed separation bubble was formed in the region 4.25<x/D<9.25, while the intermittent existence of large-scale vortices at the reduced frequency fD/U0=0.116 was identified in the upper shear layer. The convective vortex dynamics were analyzed in terms of the cross-correlation of the wall-pressure fluctuation, coherence and cross-correlation of wall-pressure fluctuations with velocity fluctuations at various positions located at the lower edge of the cylinder (y/D=G/D) and the outer edge of the upper shear layer. The convection velocities of the Karman-like vortices in the system G/D=0.5 was determined to be Uc/U0=0.64. However, in the system G/D=0.25 the convection velocities before and behind x/D=3.25 were determined to be Uc/U0=0.32 and 0.64, respectively.