Rossiter’s formula: A simple spectral model for a complex amplitude modulation process?

Spectral analysis of pressure signals recorded for high subsonic compressible flows past open cavities generally reveals frequency components of strong magnitudes (Rossiter modes). These components are not multiples of each other in the case of shallow cavities. This nonharmonic property is examined through a nonlinear modeling of the spectral distributions. For that purpose, a signal processing interpretation of the Rossiter formula is developed, which combines nonlinear distortion and amplitude modulation. The consequences of this new interpretation on the prediction of frequencies, on mode identification, and on mode interactions are discussed as well as the underlying physical mechanisms.