[antonio]

I want to simulate a density current of water/sediments in a channel that has an obstacle in the middle of it. I am using URANS and the algebraic slip model. In the beginning of the simulation I pretend to have the following condition in my domain: "clean water" in the channel (with velocity zero and hydrostatic pressure distribution). Then I want to inject a mixture of water plus sediments (the water height should be constant). To do so, I have defined in cfx a variable composition mixture of water and sediments and set "water" as the constraint. In the global initialization tab I have set all velocity components to zero, the relative pressure equal to an expression similar to the tutorial free surface flow over a bump and the sediments mass fraction to zero. My problem is that when I plot a velocity vector in a section just before the obstacle(and before the reflected current achieve that section) I have negative velocities from a given height till the free surface. This zone, that should be only composed by the ambient fluid water should have velocity approximately equal to zero. Does anyone have experienced a similar problem or can give me some hint to solve my problem?Probably i have set some input incorrectly...thanks.