Natural rivers usually possess sand waves and sand bars. In this article, the rapid distortion theory was used to study the turbulent flow over sand waves. The results show that the pre-existing sheafing motion and up...Natural rivers usually possess sand waves and sand bars. In this article, the rapid distortion theory was used to study the turbulent flow over sand waves. The results show that the pre-existing sheafing motion and upstream anisotropy of the turbulence flow would have significant effect on the turbulent structures, and hence the memory effect should be taken into consideration. Furthermore, the 2-D mathematical model was employed to simulate the unsteady flow around the Taiping Sand Bar in the lower reach of the Yangtze River and the time step effect on the unsteady flow simulation with the implicit scheme was discussed at the same time. The results show that the implicit scheme keeps effective until the time step reaches a certain number, and the calculated water levels and velocities are in agreement with the observed data.展开更多
In this paper the problem of homogeneous shearing turbulence approaching and passing an obstacle is studied by vorticity method and rapid distortion theory as well as a simple Reynolds stress model. The aim is to gain...In this paper the problem of homogeneous shearing turbulence approaching and passing an obstacle is studied by vorticity method and rapid distortion theory as well as a simple Reynolds stress model. The aim is to gain some insight into the effect of streamline curvature,initial anisotropy, upwind mean shear and relative strength of uniform mean shear on the turbulent structures over the obstacle. It is found that in the outer region of the obstacle the streamline curvature is of second order importance compared with the effect of the irrotational flow field produced by the obstacle. It is also found that for shearing turbulence passing the obstacle the pre-existing shearing motion would have significant effect on the turbulent structures. Comparing the changes in the equation for Reynolds normal stresses derived by rapid distortion theory with that derived by Reynolds stress model with the pressure strain terms of Launder, Reece and Rodi form, the two results agree approximately only when the initial turbulence is isotropic and the upwind mean shear is small.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.50539060).
文摘Natural rivers usually possess sand waves and sand bars. In this article, the rapid distortion theory was used to study the turbulent flow over sand waves. The results show that the pre-existing sheafing motion and upstream anisotropy of the turbulence flow would have significant effect on the turbulent structures, and hence the memory effect should be taken into consideration. Furthermore, the 2-D mathematical model was employed to simulate the unsteady flow around the Taiping Sand Bar in the lower reach of the Yangtze River and the time step effect on the unsteady flow simulation with the implicit scheme was discussed at the same time. The results show that the implicit scheme keeps effective until the time step reaches a certain number, and the calculated water levels and velocities are in agreement with the observed data.
文摘In this paper the problem of homogeneous shearing turbulence approaching and passing an obstacle is studied by vorticity method and rapid distortion theory as well as a simple Reynolds stress model. The aim is to gain some insight into the effect of streamline curvature,initial anisotropy, upwind mean shear and relative strength of uniform mean shear on the turbulent structures over the obstacle. It is found that in the outer region of the obstacle the streamline curvature is of second order importance compared with the effect of the irrotational flow field produced by the obstacle. It is also found that for shearing turbulence passing the obstacle the pre-existing shearing motion would have significant effect on the turbulent structures. Comparing the changes in the equation for Reynolds normal stresses derived by rapid distortion theory with that derived by Reynolds stress model with the pressure strain terms of Launder, Reece and Rodi form, the two results agree approximately only when the initial turbulence is isotropic and the upwind mean shear is small.
