Pressure Oscillations Resulting from Subsonic Flow over a Partially-Covered Cavity

Donald Wittich, Eric Jumper
2010 41st Plasmadynamics and Lasers Conference   unpublished
A series of experiments was carried out to determine if the passage frequency of coherent structures over a partially covered, rectangular cavity could be sufficiently regularized so as to make predictable the spatio-temporal optical characteristics of the shear layer. This type of passive regularization, in which no actuation is employed, had manifested itself in earlier tests as the "trapped-mode" resonance phenomenon. These more recent experiments used an acoustically treated wind tunnel to
more » ... ted wind tunnel to suppress trapped mode resonance and sought instead to excite the longitudinal standing wave modes of the partially covered cavity. The regularization was accompanied by the presence of dominant peaks in the autospectral density of cavity unsteady pressure. A modified version of Rossiter's formula, here called the "long-path" formula, was developed to describe the peak frequencies observed in the cavity pressure spectra. Flow-acoustic resonance was achieved when a natural hydrodynamic frequency (a long-path mode frequency) coincided with the natural acoustic resonance frequency of the cavity.
doi:10.2514/6.2010-4497 fatcat:gu3zeozorzhjnefalghem7aupy