Characteristics of Sound Radiated due to Flow Around a Rotationally Oscillating Cylinder

Direct simulations have been performed to study the sound field radiated due to two-dimensional unsteady flow past a circular cylinder performing rotary oscillations. Effects of forcing frequency and amplitude of oscillation on the radiated sound fields have been analyzed using higher resolution dispersion relation preserving (DRP) schemes. The computations are performed on a highly refined structured grid at a Reynolds number Re1 = 150 and Mach number M1 = 0:2. The phenomena of synchronization and non-synchronization of shedding patterns are observed. In the synchronous region, both fluctuating loads acting on the cylinder and their corresponding sound fields are completely governed by forcing frequencyratio. In the non-synchronous region, the generated sound fields exhibit modulation phenomena such that the signal is governed by forcing frequency-ratio as well as frequency-ratio corresponding to shedding frequency of a stationary cylinder for the same free-stream conditions. Directivity patterns based on root mean square (RMS ) values of disturbance pressure fields are obtained and they are found to be dipolar nature dominated by lift dipole. Various dominant modes related to sound field are obtained using the analysis of proper orthogonal decomposition (POD). These POD modes have further helped us to understand the generated sound fields in a better manner.