A simple question
 

During the simulation, reversed flow appears. In general , which parameters should I reset? And how to do that? Thanks.

Re: A simple question
 

I assume that you have pressure outlet at your domain outlet. The important is whether the back flow occurs only during solution and the back flow can disapear later in final results. If the back flow exist only temporary, a good solution is to localy patch solution during comuputation by suitable velocity and turbulence parameters. It can help. If the back flow will appear even after patching, I have two solutions for you. First is to extend computational domain to let us say a large tank. The back flow will be shift to not so important part of domain without any influence on results. The second solution should be to place the resistence downstream your outlet by porous-fluid and set the parameters for that.

Good luck, ales.