Laminar flow instabilities of a grooved circular cylinder

This paper represents a numerical study on the flow past a grooved circular cylinder with a diameter of D. The study aims to investigate the instabilities of the flow at laminar flow regimes when Reynolds number varies from 50 to 200. Three different geometrical grooves are examined, including square, triangular, and dimple. The grooves are located at $$ \theta $$  = 0°, 30°, 45°, 60° and 90°, separately relative to the front stagnation point. The effects of the groove on the flow control and imposed forces on the cylinder are studied at different Re. It is found that the presence of the groove affects the dynamic behaviour of the streamwise vortices. This behaviour leads to alteration of the pressure coefficient and a significant increment in lift coefficient, in particular for the triangular grooved cylinder. At Re = 200, the results show that the magnitude of the lift coefficient of the triangular grooved cylinder with $$ \theta $$  = 45° is 200% more than that of the square grooved cylinder. The results also reveal that the drag coefficient reduces up to 100% by employing a triangular groove shape at $$ \theta $$  = 45°. These variation in lift and drag coefficients leads to maximising the aerodynamic efficiency factor (lift-to-drag ratio) of the triangular grooved cylinder up to 200%.