hay People

how i can ileminate the negative densities in my model thanks

1. lower under-relaxation factor for pressure and/or velocity

2. enhance the number of sweeps

3. Have a look at the answers posted here in former times

If this came with unreasonable high velocity and at very beginning of iteration, you may never get rid of it with your target flow rate. Maybe, one way to get around it (I assume your mesh is OK) is to reduce your start-up flow rate to lower initial velocity. Once flow pattern developped to reasonable and stable, ram up flow rate to approach targe B.C.

Perhaps just keeping the density constant for a few 100 iterations may help.

Make sure you are using a bounded differencing scheme such as UD or MARS. In fact don't ever use a differencing scheme that isn't UD or MARS (and only use UD as a last resort)

Stephen