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

这项研究的目的是开发新的实验技术来同时测量湍流中的脉动速度和压力，评估现有的雷诺平均框架下的湍流模型，并开发与大尺度涡系结构相关的复杂湍流的计算方法。为了满足这些不同的目的，该项目被分成几个部分。发展了PIV测量和计算方法相结合的混合技术，以实验获得脉动速度和压力之间的关联。将PIV得到的速度场代入瞬时压力的泊松方程，然后用有限体积法求解各时刻的压力。对脉动速度场和压力梯度场之间的相关性的评估已经成为可能。将该方法应用于钝面…绕流的数值模拟。更多的物体在均匀的流动中串联。研究发现，过比例的强速度脉动与压力脉动有很强的相关性，现有的湍流模型由于缺乏合适的RANS框架内与压力相关的统计模型而不能描述强湍流活动。另一方面，用微型压力传感器结合热线风速仪测量的速度-压力相关性表明，相对简单的压力扩散模型不适用于湍流动能表现出强烈非平衡态的区域。基于离散涡方法的计算方法被认为是传统RANS方法和大涡模拟的替代方法。对涡旋法中常用的现有方法进行了分析，结果表明，对涡旋法稍作修改，就足以将其应用于工程湍流计算。将最初用于分子动力学模拟的专用计算机应用于涡旋法计算，显示了未来研究的一个有趣的方向。综上所述，与大尺度涡旋运动相关的湍流的动力学特征是速度场和压力场之间的强相关性。基于RANS的湍流模拟应考虑对脱离能量平衡态的复杂湍流模型的评估。较少

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