Dear evryone

my problem involves the scalar and mass,heat source, when i consider the material is hydrogen and initial value of scalar H2 in this material is 1.0, and use MARS to calculate it, then after 11 iterations. it stops, error is there are negative density at more than 100 cells. but if i set the material is Nitrogen and initial value of H2 is 0.0187, then that is ok. so what do result in it? can anyone tell me?

thank you! ragards jane

If it is a stationary calculation have you tried to lower urf for density,scalars and velocity, at least for the first 50-100 iterates? I suggest you to use CD 0.01 as differencing scheme for density, at least for the initial iterates.

I don't know the detail of your simulation, but the denisty of pure H2 is at least one magnitude smaller that the normal air. So it's easier for density to get very small and hit the problem you have. Maybe you should give more detail of your case.

see also the discussion further down:

http://www.cfd-online.com/Forum/starcd.cgi?read=4054

thank you every body! i got it

have a nice day! jane