Reynolds Stress and Heat Flux Models for Prediction Flow and Heat Transfer in Engines

为了建立雷诺应力和热流方程中扩散输运的闭合模型，测量和分析了一阶至四阶的各种类型的速度和温度脉动矩。首先，利用累积量和Hermite多项式对三维联合概率密度函数进行正交级数展开。这个PDF被发现提供令人满意的预测的统计特性，包括三重产品，湍流动量和传热。其次，利用条件采样和平均技术研究了湍流动量和热量传输过程的统计特性。对于速度和温度的三阶矩，给出了条件概率密度函数。结果表明，本文所提出的PDF格式能较详细地反映相干运动在壁面剪切流动动力学及相应的湍流热输运过程中的作用。特别是，相干运动的雷诺应力分量和热通量的湍流扩散过程中的重要性，证明了第一次由本理论。

To develop a closure model of diffusion transport in the Reynolds stress andheat flux equations, various types of moments of velocity and temerature fluctuations of the first to the fourth order have been measured and analyzed. First,and orthogonal series expansion for the three-dimensional joint probability density function (pdf) is developed using the cumulants and Hermite polynomials. This pdf is found to provide satisfactory predictions for the statistical characteristics, including triple products, of turbulent momentum and heat transfer. Next, the conditional sampling and averaging technique is employed to investigate the statistical characteristics of coherent turbulent transfer processes of momentum and heat. Conditional pdfs are developed for various moments of velocityand temperature up to the third order. It is showm that the present pdfs can represent the detailed role of coherent motions in the dynamics of wall turbulentshear flows and in the relevant process of heat transport by turbulence. In particular, the importance of coherent motions in the turbulent diffusion process of Reynolds stress components and heat fluxes is demonstrated for the first time by the present theory.