Higher-Order Turbulence Around Different Circular Cylinders Using Particle Image Velocimetry

Abstract

Wakes and higher-order turbulence around circular cylinder of different diameters are investigated using particle image velocimetry measurements. The cylinder Reynolds number (Red) is defined by the depth averaged velocity, cylinder diameter and kinematic viscosity. The influence of Red on third-order moment of velocity fluctuations, turbulent kinetic energy (TKE) flux, TKE budget and turbulent length scales are presented. The intermittency factor and quadrant analysis around the cylinders are discussed for Red values ranging from 12,600 to 21,000. Intermittency factor increased with Red. Red effect modulated the energy budget mainly near free surface upstream and near bed downstream. Stream-wise and transverse TKE fluxes decreased significantly with Red, but not the vertical flux. Stream wise skewness changed sign from positive to negative with a certain critical distance on downstream, while vertical skewness showed reversed with Red. Negative stream-wise skewness and positive vertical skewness indicate the occurrence of ejection events. Production and dissipation rates increased with Red on the downstream, whereas opposite trend was observed for dissipation on the upstream. Increase of Red led to increase in Kolmogorov length-scale much higher on the upstream than downstream, whereas it showed depleting effect on Taylor's length-scale on upstream and increasing effect on the downstream. Ejection and sweep events were more prominent in the downstream near the cylinder than upstream with higher values of shear stress on the downstream. The sum of shear stress contributions of all quadrant events increased consistently with increase in Red near the cylinder.