PHENOMENOLOGICAL MODELING BASED ON THE MEASUREMENTS OF INSTANTANEOUS PRESSURE FIELD FOR PRESSURE-RELATED STATISTICS IN TURBULENT FLOWS OUT OF THE EQUILIBRIUM STATE

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The objectives of the study are to develop novel experimental techniques for the simultaneous measurements of fluctuating velocity an d pressure in turbulent flows, to assess the existing turbulence models in the Reynolds averaging framework, and to develop computational methods to predict complex turbulent flows associated with large-scale vortex structures. The project has been accordingly separated into several parts to cover these diverse purposes.The hybrid technique combining PIV measurement and computational approach has been developed to experimentally obtain the correlation between the fluctuating velocity and pressure. The velocity field obtained by PIV is substituted into the Poisson equation for the instantaneous pressure which is then solved by use of a finite-volume method at every instant. The evaluation of the correlation between the fluctuating velocity and pressure gradient fields has been possible. This method has been applied to turbulent flow around a pair of bluff … More bodies set in uniform flow in tandem. It is found that the over-proportionally strong velocity fluctuation is strongly correlated with the pressure fluctuation, and the currently existing turbulence models cannot represent the strong turbulent activities due to the lack of the appropriate model for the pressure-related statistics within the RANS framework. On the other hand, the measurement of velocity-pressure correlation by a miniature pressure sensor combined with an X-hot wire anemometer has indicated that the relatively simple model for pressure diffusion may not be applied to the region where the turbulent kinetic energy exhibits strong non-equilibrium state.Computational approach based on the discrete vortex method is considered as an alternative to the conventional RANS approach and to LES. The currently available methodology which is common in vortex method community has been examined and it is shown that some minor modification would be sufficient for the vortex methods to be applied to engineering turbulent flow computations. The application of the special purpose computer which is originally developed for the molecular dynamics simulations to vortex method calculation has shown an interesting direction of the future research.In summary, the dynamics of the turbulent flows associated with large-scale vortex motion is characterized by the strong correlation between the velocity and pressure fields. The turbulence modeling based on RANS should take into account the assessment of the models in complex turbulent flows out of energy equilibrium state. Less