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，测量和分析了各种类型的一阶至四阶速度和温度波动矩。首先，利用累积量和埃尔米特多项式对三维联合概率密度函数（pdf）进行正交级数展开式。发现该pdf对湍流动量和传热的统计特性，包括三重积，提供了令人满意的预测。其次，采用条件采样和平均技术研究了动量和热量相干湍流传递过程的统计特性。对于速度和温度的各种时刻，开发了条件pdf，直到三阶。结果表明，本文导出的pdf格式能较好地反映出相干运动在壁面湍流剪切流动动力学和湍流热输运相关过程中的作用。特别是，本理论首次证明了相干运动在雷诺应力分量和热流的湍流扩散过程中的重要性。

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.