Three-dimensional numerical simulation of hydrodynamic forces on an oblique cylinder in oscillatory flow

Sinusoidal oscillating flow around a circular cylinder at an oblique angle is investigated by direct numerical simulation. Simulations are carried out for oblique angles of α = 0°, 15°, 30°, 45° and 60°, Reynolds number Re = 2000 and KC number ranging from 6.75 to 30. The oblique angle is defined as the angle between the flow direction and the transverse plane of the cylinder (see Fig. 1). The predicted vortex shedding regimes agree well with those found from physical experiments. When the KC number is close to the boundary value of KC number between two vortex shedding regimes (KC = 6.75, 15, 20 and 30) the correlation of sectional force in cylinder's spanwise direction is very weak and the time series of the transverse force contains two or three predominant frequencies, implying the flow switches from one mode to another continuously. The span-wise correlation factor obtained according to the sectional transverse force is always close to 1 for single-mode flows. Comparison between the numerical results of α=0° and those of α≠0° shows that the independent principle is applicable for the calculated KC number range and the oblique angle ( α≤60°). The oblique angle has little effect on mode-averaged transverse force and the in-line force coefficients.