how to adjust solid distribution

hx

Hi everybody, I am working on porous media filtration using Eulerian multipahse model.we think that the solid phase will suspende in the whole body of the vessel and be dense near the outer surface of the filter element. But the result is that all the solid phase settles on the filter surface. there is no solid phase in the other part of the vessel. Could somebody tell me why this happend?. Thanks a lot