Wake and acoustic responses of a circular cylinder to freestream fluctuations

An upstream turbulence/fluctuation has been shown to increase the unsteadiness in the wake of a three-dimensional bluff body (Mittal, 2000). This inevitably will influence the radiated acoustic waves in the far field. In this paper, the effects of fluctuating freestream disturbances on the wake structure and sound radiation from a two-dimensional flow over a circular cylinder are investigated. The flow field is obtained by numerically solving the incompressible Navier-Stokes equations. At a Reynolds number of 40, the addition of fluctuating disturbances in the freestream causes the otherwise steady wake to oscillate at the frequency of the disturbance. This oscillation is enhanced with increasing energy and frequency of the fluctuations. The corresponding acoustic field is obtained by using an Expansion about Incompressible Flow (EIF) method. The computed acoustic field shows a dipole directivity, which is similar to that of a natural vortex shedding. Moreover, using the rms plot of the fluctuations of the EIF source terms, the location of the dipole source in the wake of the cylinder is accurately identified.