Development of Second-Moment Closure with Comprehensive Testing

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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.