Lattice Boltzmann Simulation Of The Flow Around A Circular Cylinder

The lattice Boltzmann method (LBM) is employed to investigate the flow past a circular cylinder under some flow conditions including steady uniform flow, sinusoidally oscillating flow and linear shear flow.The influences of grid resolution, the width of the domain and outflow boundary condition on the numerical results are discussed. An implementing method of the convective boundary condition is presented. This method has less influence on the inner flow, but it will introduce numerical instability at high Reynolds number.For the steady uniform flow around a circular cylinder, the calculated vortex shedding frequencies and drag coefficients agree with experimental results at Reynolds numbers lower than 300. For high-Reynolds-number flows, the combined model of LBM and large eddy simulation method is adopted. Although the simulation is stable with this combined model, the vortex structures and the force coefficients are different from the results of experiments and other three dimentional numerical models.For the oscillating flow around a circular cylinder, it is not appropriate to adopt velocity condition to drive the flow, while the oscillating flow can be produced correctly with an oscillatory body force, which is employed to simulate the oscillating flow aroud a circular cylinder in this thesis. The emergence mechanism and characteristics of steady streaming are analyzed.The linear shear flow past a circular cylinder is simulated at Reynolds number of 100 and shear parameters up to 0.1. The influence of the shear effect on the vortex structure, vortex shedding frequency, drag coefficient and lift coefficient is discussed. The numerical results indicate that the vortex shedding persists at the shear parameters up to 0.1 for this Reynolds number. There is a non-zero lift force acting from the high velocity side toward the low velocity side in the shear flow.