Nonlinear resonant interactions in internal cavity flows

Reference is made to an investigation of some of the flow mechanisms involved in acoustic energy production by vortex shedding carried out by Isaacson and Marshall (1982). This produced measurements of oscillating velocity frequency spectra indicating that in certain flow regimes velocity oscillations occur which satisfy the frequency resonant interaction. Results are presented here of bispectral cross-power measurements of trios of frequencies occurring in an internal cavity in a turbulent flow. These measurements provide additional evidence that the trios of frequencies are of quadratic interaction origin. The measurements are made in a subsonic wind tunnel driven by a centrifugal fan that drives air into a settling chamber that is 0.61 m on each side and 1.22 m long. The settling chamber is segmented and contains four damping screens that act to reduce the turbulence of the flow into the test section.