Drag prediction in the wake of a linearly tapered rotationally oscillating cylinder

Experimental results on drag estimation of a rotationally oscillating tapered cylinder are presented at Reynolds number of 250 (based on mean diameter,$D_m$). The cylinder used in the present experiments has a taper ratio of 70:1 and a mean diameter of 8mm. The drag is obtained using mean and fluctuating velocities acquired from Particle Image Velocimetry. Drag coefficient, C$_D$, is estimated using the momentum deficit formula. Validation results for the untapered cylinder are found to agree with published data in the present Reynolds number regime. The tapered cylinder is forced to oscillate at various forcing frequencies(FR) and oscillating amplitude of $\theta_{0}$=$\pi$/2 and $\theta_{0}$=3$\pi$/4. It was observed that the range of forcing frequencies for which the wake is locked onto the cylinder frequency increases with increasing oscillation amplitude. When the forcing frequency enters the lock-on zone, maximum values of C$_D$ are obtained, and with further increase in forcing frequency the C$_D$ decreases.