LAUSR

Abstract This study deals with the influence that different motion laws have on mixing enhancement downstream of a moving square cylinder in the confined laminar regime. A square cylinder, connected to a cam system and a motor, was placed inside a square section channel. The blockage ratio was 0.4 and the flow Reynolds number (Re), based on the cylinder square section length, was 200. Three different cams were considered, and this led to three different motion laws: sinusoidal, cycloid, y step-like. The peak to peak amplitude of the motion was kept constant (equal to half the side length of the cylinder) and the frequency was varied around the wake instability natural frequency (f0) of the flow past the unmoving cylinder prior to the onset of the vortex shedding regime. A Particle Image Velocimetry (PIV) system was used to characterize the flow. PIV snapshots were used to compute traces in which virtual particles were shed; then, a mixing parameter was defined that relied on counting these virtual particles at sections located downstream of the cylinder. It was found that the most efficient mixing took place when using the step-like motion law at a frequency equal to f0. The less efficient mixing occurred when implementing the sinusoidal motion at a frequency equal to 0.5 f0. Generally speaking, increasing the frequency of the motion did not necessarily lead to better mixing efficiency.