Numerical investigation of flow past a circular cylinder modified with a single groove at low Reynolds number

Abstract

Flow past a circular cylinder modified by grooves is one of the passive control techniques to control the drag and lift forces. The presence of grooves tends to reduce the hydrodynamic drag and lift. The aim of this work was to numerically investigate the influence of a single groove modification on a circular cylinder and how it was impacting the hydrodynamic coefficients based on its position and shape at low Reynolds numbers. Three types of grooves were considered, namely, dimple, square, and triangular, with identical width and depth which is 0.1 times the diameter. The Reynolds numbers considered were 100, 150, and 200. The computational domain was set to a blockage ratio of 0.01 after carrying out a detailed domain independence test. It was observed that the drag and lift reduction was maximum at groove location 90° with the decrements being more for the square groove shape. The viscous drag showed a decrease in its values for all the groove positions located on the flow-facing side of the cylinder; however, the pressure drag showed an increment in its values for these groove locations, and these increments were relative of larger magnitudes, thus influencing a net increase in the total mean drag when compared to the smooth case; this was evident at groove locations 120° and 150°. The vorticity patterns for the grooves located on the front side showed large irregularities in magnitude between the anticlockwise and the clockwise vortices with the groove side vortices being of larger magnitudes, and for the wake side, the irregularities were negligible. The coefficient of pressure and separation angles were also investigated. The CP vs θ plots showed discontinuity at groove locations with abrupt variations at the front face of the cylinder; for the wake side grooves, these discontinuities were low and almost coincided with the CP vs θ plots of the smooth cylinder. The grooves located at 90° showed a delay in separation and at 60° the boundary layer tends to detach earlier.