Three-dimensional flow oscillations in a supersonic cavity are investigated by the numerical simulation based on the Navier-Stokes equations. The dominant frequencies of the pressure fluctuation calculated by this simulation agree very well with those measured in the previous experiments. In order to extract the fluctuating components of the dominant frequency, time-dependent solutions are phase-averaged. With this method, three-dimensional behaviors of the oscillating cavity flow are clearly visualized. The visualization result reveals that the unsteady motion of the shear layer is not uniform along the duct span due to the existence of two sidewalls. This non-uniformity makes acoustic wave generation localized on the cavity trailing edge in the vicinity of the duct center, and consequently produces the highly three-dimensional pattern of the standing wave in the cavity.

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A modal wavelet transform, which overcomes the intrinsic data number limitation of power of two to conventional wavelet transform, has been applied to analysis of pseudo and standard PIV images. The modal wavelet transform is compared with the discrete wavelet transform in order to select the best base function among Neumann, Dirichlet and Green function types base functions. Consequently, it is verified that Neumann type base function is the best because the correlation of Neumann type base function is high and the root mean square is lower than the other base functions. Also, the decomposition vector patterns by Neumann type is similar to that by conventional Daubechies base function of 4^th order.

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