Publications

Resonance characteristics of transonic flow over a rectangular cavity using pulse-burst PIV

Beresh, Steven J.; Wagner, Justin W.; DeMauro, Edward P.; Henfling, John F.; Spillers, Russell W.

Pulse-burst particle image velocimetry (PIV) has been used to acquire time-resolved data at 37.5 kHz of the flow over a finite-width rectangular cavity at Mach 0.6, 0.8, and 0.94. Power spectra of the PIV data reveal four resonance modes that match the frequencies detected simultaneously using high-frequency wall pressure sensors. Velocity resonances exhibit spatial dependence in which the lowest-frequency acoustic mode is active within the recirculation region whereas the three higher modes are concentrated within the shear layer. Spatio-temporal cross-correlations were calculated from velocity data first bandpass filtered for specific resonance frequencies. The low-frequency acoustic mode shows properties of a standing wave without spatial correlation. Higher resonance modes are associated with alternating coherent structures whose size and spacing decrease for higher resonance modes and increase as structures convect downstream. The convection velocity appears identical for the high-frequency resonance modes, but it too increases with downstream distance. This is in contrast to the well-known Rossiter equation, which assumes a convection velocity constant in space.