This chapter studies the role of pressure-velocity correlation in oscillatory flow between a pair of bluff bodies. Turbulence models based on the Reynolds-averaged Navier-Stokes (RANS) approach often fail to predict flows associated with massive separation, in contrast to large eddy simulation (LES) that correctly captures large-scale turbulent fluid motion typically found in such flows. It is generally recognized that the poor performance of the RANS models is due to the shortcomings of the statistical approach itself in representing the coherent structure in turbulence. This chapter considers turbulent flow measurements between two bluff bodies set in uniform flow in tandem arrangement. The velocity obtained with particle image velocimetry (PIV) are averaged with respect to either time or phase of periodic pressure oscillation induced by vortex shedding from the bluff body, that is, Reynolds decomposition or three-level decomposition. The Reynolds stress caused by periodic fluid motion is found excessively large compared with those related to turbulent fluctuation in entire flow field. The PIV data is used to solve discrete Poisson equation of instantaneous pressure. The effect of organized vortex motion is recognized as the strong correlation between velocity and pressure gradient, which explains the poor performance of RANS turbulence models in predicting this kind of flows.
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