Modified quadratic stochastic estimation of resonating subsonic cavity flow

There is an obvious need for the development of reduced-order time-resolved models of the off-body physics of wall-bounded shear flows. This work represents a preliminary step toward producing such a model for the resonating subsonic cavity flow by presenting the modified quadratic stochastic estimation (mQSE) as a means to estimate flow field quantities using surface pressure measurements. The mQSE estimates these flow field quantities using statistics calculated between surface-pressure fluctuations and the flow field's POD expansion coefficients. In the current work, the mQSE is applied separately to both the velocity and density fields for subsonic flow over a resonating cavity. The velocity data are obtained using particle image velocimetry, while the density gradients are obtained using spark Schlieren photography. The results demonstrate the ability of the mQSE to estimate the structure of the complex cavity flow field using a few wall-pressure measurements. The results also show an interaction between the hydrodynamic and acoustic features that may be related to mode switching which shifts the dominant energy from one frequency to another in time.