Realizability in Turbulence Modelling for Turbomachinery CFD
Realizability in Turbulence Modelling for Turbomachinery CFD
复制标题
涡轮机械 CFD 湍流建模的可实现性
DOI：
10.1115/99-gt-024
复制
发表时间：
1999
期刊：
影响因子：
--
通讯作者：
J. Moore
中科院分区：
文献类型：
--
作者：
J. Moore;J. Moore
显然，雷诺法向应力显示公式在所有方向上都应始终为正，即计算的紊流应力应是可实现的。然而，常用的两方程湍流模型不包括可实现性。它们取紊流粘性系数为cμ k ~ 2/e，cμ a为常数，在紊流的名义无粘段中，远离壁面处经常产生负的法向应力。由于前缘滞止和叶片转动引起的压力梯度产生了一个无粘应变场。这些应变导致在流场的重要部分上计算负正应力。其结果可能是前缘上游的湍流动能错误地增加了10倍或更多。这种错误的湍流然后在叶片周围对流并通过叶片排，显著影响计算的边界层发展和叶型损失。通常，通过在进口处使用人为的高耗散e值来避免生产过剩的问题。但当湍流模型中包含可实现性时，就不需要这种不正确的过程了。通过压气机和涡轮机叶栅的实例说明了问题的严重性及其解决方法。
It is obvious that the Reynolds normal stresses Display Formulauu¯ should always be positive in all directions, i.e. the computed turbulence stresses should be realizable. However, the commonly used two-equation turbulence models do not incorporate realizability. They take the turbulent viscosity as cμk2/e with cμ a constant, and frequently generate negative normal stresses far from walls in the nominally inviscid sections of turbomachinery flows. Pressure gradients due to leading edge stagnation and blade turning create an inviscid strain field. These strains cause the calculation of negative normal stresses over significant portions of the flow field. The result can be erroneous increases in turbulence kinetic energy upstream of the leading edge by a factor of ten or more. This erroneous turbulence is then convected around the blade and through the blade row, significantly affecting the computed boundary layer development and profile losses.Frequently the problem of overproduction is avoided by using artificially high values of the dissipation, e, at the inlet. But this incorrect procedure is not needed when realizability is incorporated in the turbulence model.The paper reviews some methods and models which ensure realizability in two-equation turbulence models. The extent of the problem and its solution are illustrated with examples from compressor and turbine cascades.Copyright © 1999 by ASME