Flow/acoustic interactions of two cylinders in cross-flow

The noise generated by two tandem cylinders in a cross-flow (i.e., with the second in the wake of the first) has been investigated. Measurements of turbulence and of fluctuating pressure have been obtained between the two cylinders for different flow velocities and incident levels of turbulence. Although, for a number of cases, up to four peaks related to vortex shedding were evident in the spectrum, most measurements exhibited two peaks, a dominant one at the vortex-shedding frequency, with a secondary peak at twice this value. The measurements show that vortex generated noise is strongest at the mid-point between the cylinders and at the rear cylinder with levels of 130 dB. The harmonic component was strongest at the downstream cylinder where peak values of 110 dB were obtained. The nonlinear 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 nonlinear interactions which give rise to noise at harmonics of the vortex-shedding frequency.