Development of Second-Moment Closure of High Performance

点击翻译按钮获取中文摘要

The purpose of this project is to develop a turbulence model which reproduces a wide range of turbulent flows by testing and refining a low-Reynolds-number second-moment closure without wall-reflection redistribution terms proposed by Shima, the head investigator of the project, in 1997.The second-moment closure (Model 97) has been tested in channel flows with spanwise, streamwise and wall-normal rotations, unsteady pipe flows, flows through concentric annuli, and periodically transpired channel flows. Direct numerical simulations (DNS) of the flows with system rotations and flows through concentric annuli have also been performed, and databases of these flows have been constructed. The model 97 reproduces the concentric annulus flows well, and also shows a clear superiority to eddy-viscosity models in the periodically transpired channel flows. In the unsteady pipe flows, however, the model gives less accurate response of turbulence to flow-rate variation than a Shima's previous model which includes wall-reflection terms. In the case of weak streamwise rotation, the predicted velocity profiles are in reasonable agreement with DNS data. At high rotation rates, however, the predicted sign of a shear stress component disagrees with that of DNS, leading to poor predictions of the velocity profiles. The wall-normal rotation leads to relaminarization of the flow when the rotation rate becomes high. Good predictions are obtained for weak rotation but the model gives relaminarization at a lower rotation number than DNS. As we have seen, the model 97 shows several weaknesses, though it is useful in many flows as a low-Reynolds-number second-moment closure without wall-reflection redistribution terms. Based on these results, we are developing a new model for higher performance.