Impact of the downstream cylinder displacement speed on the hysteresis limits in a flow around two rectangular objects in tandem - PIV study of the process

This paper is about experimental study of air flow around two identical square cylinders arranged in tandem with the use of particle image velocimetry approach. Impact of progressive increase and progressive decrease in the spacing between centres of the cylinders (ranging from 2 to 9 widths of the cylinder) on a hysteresis limit were investigated. The hysteresis is associated with two discontinuous jumps in the flow patterns and occurs when the spacing between cylinders varies in two ways. Particular attention was devoted to the study of the downstream cylinder displacement velocity (ranging from 0.01 to 0.09 m/s) on the hysteresis range for different free-stream Reynolds numbers (Re = 4100-32940). The changes in the flow pattern were determined based on the time histories of velocity fluctuations analysed independently in the most characteristic regions of the measuring section. The impact of the downstream cylinder velocity and the Reynolds number on the lower and the upper spacing limits of the hysteresis was presented and discussed.