Development of Second-Moment Closure with Comprehensive Testing

这个项目的目的是通过测试和改进一个低雷诺数第二弯矩闭包，该闭包没有壁面反射再分布项，从而开发一个湍流模型，该模型再现了大范围的湍流流动，该闭包由项目的首席研究员Shima于1997年提出。第二弯矩闭合（模型97）已经在各种具有工程重要性的湍流中进行了测试。目标流之一是直管中的湍流旋流。用模型97预测了一种典型的切向速度剖面为组合无强迫涡型，轴向速度剖面在核心处有低速区的流动。该模型捕捉到了入口区域漩涡速度的衰减和核心轴向速度的恢复，但在下游区域，与测量结果相比，它对非漩涡流动的恢复太慢。当引入UMIST小组提出的与对流相关的再分布项时，湍流模型在入口区域返回的衰减太快，导致与下游区域的实测衰减一致。我们得出结论，对流相关项的系数应该优化，以获得最佳的整体性能。模型97还对流线曲率、边界层壁面蒸腾和通道流动的影响进行了预测，结果表明，该模型较好地再现了实验结果和DNS结果。我们目前正在环流、三维边界层、不同旋转轴的通道流、非定常流和绕其轴振荡的管流中对该模型进行测试，旨在为开发有用的高普遍性湍流闭包奠定坚实的基础。

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 a variety of turbulent flows of engineering importance. One of the target flows is turbulent swirling flow in a straight pipe. A typical flow in which the tangential velocity profile is of a combined forced-free vortex type and the axial velocity profile has a low velocity region in the core has been predicted with the model 97. The model captures the decay of the swirl velocity and the recovery of the core axial velocity in an inlet region, but in the downstream region, it gives too slow recovery to a non-swirling flow as compared to measurements. When a convection-related redistribution term proposed by the UMIST group is introduced, the turbulence model returns too rapid decay in the inlet region, leading to the agreement with the measured decay in the downstream region. We conclude that the coefficient of the convection-related term should be optimized to obtain the best overall performance.The effects of streamline curvature and wall transpiration in boundary layers and channel flows have also been predicted with the model 97, and it has been found that the model generally reproduces experiments and DNS well.We are now testing the model in annular flow, three-dimentional boundary layers, channel flow with different axes of rotation, unsteady flow and pipe flow oscillating around its axis, aiming at constructing a firm basis for the development of a useful turbulence closure of high generality.