Effects of circumferential groove spacing on flow over a circular cylinder: a large eddy simulation

The effects of the spacing between circumferential grooves on the flow past a circular cylinder are investigated by large eddy simulation at a fixed Reynolds number of 3900. Grooves of a fixed geometry are evenly distributed over either the middle half-span or the whole span of the cylinder (hereinafter referred to as half-covered or fully covered cylinder respectively). It is found that the turbulent kinetic energy of the vortical structures around both fully covered and half-covered cylinders first increases and then decreases with increasing number of grooves (i.e., with reducing groove spacing). For the fully covered cylinders with groove spacing ratios (the ratio of groove spacing over groove height) greater than 3, the turbulence in the flow field increases with increasing number of grooves distributed along the span. For groove spacing ratios less than 3, a reduction of flow turbulence is observed on the bare sections with increasing number of grooves, resulting in an overall flow field with lower turbulence. For the half-covered cylinder, significant spanwise flow is formed on both sides of individual grooves. Further, two large and localised regions with significant spanwise velocity emerge at the two ends of the grooved section when the groove spacing ratio is lower than 8.75, and these localised regions expand with increasing number of grooves distributed in the middle section. The findings of the present investigation may be adopted to guide the design of passive flow control strategies. • Spanwise flow dynamics differ between full and half-groove coverage. • Groove spacing ratio critically influences wake turbulence and flow forces. • Turbulence shows a non-monotonic trend with increasing groove number. • Findings support groove design strategies for drag and vibration control.