Non-linear flow/acoustic interactions for two cylinders in cross flow

This paper examines techniques for determining the non-linear interactions in the unsteady velocity field and between this and the acoustics for two cylinders in cross flow. Measurements for the unsteady flow have been obtained with hot film anemometry and freestream pressure fluctuations have been monitored using a microphone. The non-linear flow/acoustic interactions are examined using bispectral analysis to identify the quadratic interactions in the parameters. A novel quadratic modelling method is proposed and shown to be capable of both identifying and quantifying the non-linear interactions which give rise to noise at harmonics of the vortex shedding frequency.