| Subsonic flow over a rectangular cavity with a length-to-depth ratio of 6 and an 8.0 mm depth is studied experimentally to gain insight into the relationship between the wall-pressure loads and the flow field dynamics. The data was collected along the centerline of the cavity at free-stream Mach numbers ranging from 0.2 to 0.8 using wall mounted pressure transducers, 2-D Particle Image Velocimetry (PIV), and spark Schlieren photography. The cavity flow data is analyzed using Proper Orthogonal Decomposition (POD), two-point time-dependent correlations, and the modified Quadratic Stochastic Estimation (mQSE) which allows the temporal dynamics of the flow to be estimated using the measured wall-pressure fluctuations as estimators. These analyses are used to determine the flow field sources that are related to the wall-pressure loads and determine how these sources are related to the periodic nature of a resonating cavity. The mQSE estimation demonstrates the phenomenon of mode-switching and shows how the wall-pressure loads are related to vortex motion as well as downstream and upstream propagating density gradients which move with the shear-layer convection and the acoustic speed respectively. In general that the shear-layer oscillation, vortex convection, and flow impingement are shown to be directly related to the measured pressure loads. Following Kraichnan (1956), Poisson's equation is applied to the estimated velocity fluctuations to calculate the wall-pressure loads resulting from the linear and non-linear source terms. The results show that the linear term has a much stronger impact on the wall-pressure and exhibits the periodicity associated with the Rossiter modes. In contrast, the non-linear contribution is found to be smaller in magnitude and primarily broadband in nature. |
