Statistics fo Dynamic Pressure Measurements in a Rectangular Cavity

Historically, record length and processing methods have limited the physics that can be extracted from a dynamic pressure measurement in a rectangular cavity.  Limited record length, window size, overlap, and averaging have produced resulting spectra with sharp tonal peaks and relatively smooth broadband noise.  This has led to a simplified understanding of the cavity, even though CFD and numerous non-intrusive experimental methods have shown different spectral features.  A recent experiment captured 8 seconds at Mach 0.7 and 15 seconds at Mach 1.5 of dynamic pressure measurement at 100 kHz sample rate in a rectangular cavity with a Length to Depth ratio of 5.6.  The Reynolds number for both Mach numbers were 2e^6/ft.  Using statistical analysis we will show how the tonal peaks vary in both the frequency and amplitude when the window size is varied.  Using histograms we will show that the historical average may not be the statistical average.