LES calculation for uniform flow past a rotationally oscillating cylinder

Two- and three-dimensional computations of flow past a rotationally oscillating cylinder are carried out at Re=150 and 1.5×1041.5×104, respectively, to study the effectiveness of drag reduction through rotary oscillation of a cylinder. The turbulent wake is modeled by an LES technique. Two forcing amplitudes Ω=0.5Ω=0.5 and 2 with a wide range of forcing frequency fe are considered. The mean drag has a sharp increase during the lock-on range, and then decreases continuously to a minimum value. Up to 57% of drag reduction is achieved at Re=1.5×104Re=1.5×104. As the forcing frequency further increases, the effect of cylinder oscillation diminishes and the mean drag approaches the value of flow past a stationary cylinder. Several different wake patterns, due to the variation of forcing frequency fe, are observed by computational streaklines.