说明：  这个算例采用格子Boltzmann方法模拟不稳定绕柱流的情况。在固体边界出采用反弹格式进行处理。
(this example examines an unsteady flow past a cylinder placed in a channel. The cylinder is offset somewhat from the center of the flow to make the steady-state symmetrical flow unstable. At the inlet, a Poiseuille profile is imposed on the velocity, where as the outlet implements an outflow condition: grad_x p = 0. At Reynolds numbers around 100, an unstable periodic pattern is created, the Karman vortex street.)