Research On The Problem Of Multiple Turbulent Spots In The Near Wall Region

The generation and evolution processes of the multiple turbulent spots in the near wall shear flow are researched by the direct numerical simulation (DNS) method of Navier-Stokes (N-S) equations which are used as the control equations of the flow in the thesis.The finite difference method with higher order and high resolution is employed to study the problem of the multiple turbulent spots. The system of equations, which is used to solve numerically the N-S equations, is composed of a forth-order time-splitting scheme and a three-dimensional coupled forth-order upwind compact scheme. Because the wall disturbance is an important factor of stirring up turbulent spots, the wall velocity pulse induced by the rough wall surface is chose as an initial model in present thesis, and is set up according to different problems. Different boundary conditions are processed carefully to retain the computational accuracy and numerical stability. These methods are applied in the overall flow domains including boundary neighbourhood.The problems of multiple turbulent spots with various combinations are emphatically studied. In the thesis, the amplitude of the disturbance, Reynolds stress, velocity vector, planar vortex, vibrating frequency as well as the developing and changing process of other terms of the Navie-Stokes equations, especially the main characteristics of the nonlinear evolution and the rule of influence each other, are studied by changing the allocation of disturbance source and the value of the wall pulse. Further more, the development and evolution of double spots, and multi-spots are compared with a single spot, and analyzed in detail. Two-dimensional animations based on different angles are designed by using data of the DNS.The discovery of the turbulent spot is a new progress of modern transition and turbulence studies, and is a leading problem. These researches in depth have contributed to explore the mechanization of the formation and the maintenance of the flow transition and the turbulence, and promoted the application of the flow controlling. Relative research works possess important theoretical sense and applicable prospect.