Evolution Of Two-dimensional Circular Cylinder Wake Between Parallel Walls

Flow around a bluff body, existing widely in nature and in industries, is one of the hottest and most difficult problems in the field of engineering fluid mechanics. Some flow mechanisms have not been thoroughly made clear due to the complexity of bluff body wake, and thus it is of great academic significance to study the flow around a bluff body. At the same time, as for industrial equipments with fluid flowed around, vibrations of the bluff body may be caused. It makes fatigue damages to the bluff body which may bring about equipment fault. Therefore, study of the flow around a bluff body has special significant realistic meanings to improve the reliability and security of long-time running characteristics of equipments in modern industries.In this dissertation, two-dimensional flow around a circular cylinder between parallel walls was studied, and a two-dimensional numerical model for the flow around a circular cylinder was built by using the computational fluid dynamics code FLUENT. Adopting appropriate grids and algorithms, the wake evolution characteristics of two-dimensional flow around a circular cylinder between parallel walls was simulated in the case that Reynolds number is less than 600. The critical Reynolds number of flow pattern transition was obtained, and the impact of the blockage ratio (β) and Reynolds number (Re) on the flow field parameters was analyzed.The main conclusions of this study are as follows:(1) The multi-block structured girds and the combination of SIMPLEC, second-order pressure discretization, and QUICK are found to be more appropriate for the simulation of the two-dimensional flow around circular cylinder at low Reynolds numbers between parallel walls.(2) By simulating flow around circular cylinder between parallel walls withβof 0.28, it is found that when Re<9, there is no separation in the flow behind the cylinder; when 9≤Re＜70, there is a steady and symmetric pair of vortices in the wake flow, as the Reynolds number increases, the separation points of vortices move upstream and the length of wake and backflow areas both increase; when Re>70, the vortices in the wake flow begin to shed from the circular cylinder and form vortex street.(3) By computing flow around circular cylinder in the range of 0.05≤β≤0.28, and analyzing the impact ofβon the parameter of flow field, it is found that when 0.05≤β＜0.1, the critical Reynolds numbers of flow pattern transition remain the same from non-vortex to a pair of vortices; when 0.1≤β≤0.28, the critical Reynolds numbers increase asβincreases when flow pattern transform from non-vortex to a pair of vortices. Moreover, in the range of 0.05≤β≤0.28, the critical Reynolds numbers of flow pattern transition from a pair of vortices to vortex street increases asβincreases. Under the same Reynolds number, the separation points of a pair of vortices move downstream as the width between parallel walls decreases, and the wake length decreases.