Numerical Study On The Flow Around Bluff Bodies With Lattice BOLTZMANN Method

In engineering practice, there are many problems which have close relationship with the unsteady flow of bluff bodies. Especially for complex flow field, such as the confined flow around a bluff body in a channel, the flow around a bluff body near the solid wall, as well as the flow around bluff bodies. The studies of these phenomena have great attention of scientists. In this paper, a new method of calculation and simulation for fluid flow developed in recent years—lattice Boltzmann method (LBM) has been applied for low Reynolds number case, the complex flow around bluff bodies have been studied systematically.In this paper, the numerical simulation for the Reynolds number: Re = 100 and 200 cases, flow around a single square cylinder placed in no confined flow field has been investigated. The results have been obtained, for example, drag coefficients, lift coefficients and the vortex shedding cycle number, Strouhal number (St), which have been compared with the existing experimental results and other numerical simulation results. The study not only verifies the applicability of lattice Boltzmann method for solving such problems, but also validates the accuracy of the later work.Next, this paper simulated phenomena of the flow around a square cylinder confined in a two-dimensional channel is investigated for Re=100 with the lattice Boltzmann method. Three blockage ratios are considered. The effect of the channel walls on the drag and lift coefficients of the cylinder, the Strouhal number and the vortex patterns in the wake of the cylinder is examined. The variations of the coefficients and the Strouhal number with the blockage ratio are presented. It is found that both the drag coefficient and the Strouhal number increase with the blockage ratio while the lift coefficient decreases. The results are compared with related experimental data in literature and a good agreement is achieved. Secondly, the flow characteristics of two tandem square cylinders confined in an unbounded domain and a two-dimensional channel (Re=100) have been simulated. The effect of gap ratios and blockage ratios has been studied. The drag, lift coefficients of the cylinders and their Strouhal number are presented. It is found that there exists the critical gap ratio, which is defined as the distance between the centers of two cylinders, beyond which the vortex shedding from the upstream cylinder occurs. In particular, in the case of two tandem square cylinders in channel, there is no vortex shedding from cylinders when the gap ratio is under the critical one, only beyond which the vortex shedding from both of cylinders occurs. Besides, the blockage ratio of channel has played an important role in the flow characteristics of two tandem cylinders. Finally, the numerical simulation was performed to investigate the effect of the flow structure in the wakes of rectangular cylinders placed near a plane with lattice Boltzmann method (Re=200). The lift and drag coefficients and Strouhal numbers were investigated. The results show that vortex shedding suppression occurs and wake becomes steady up to a certain value of Reynolds number at a critical gap ratio.