negative densities.
 

HI, I'm performing a full cycle IC Engine simulation under motoring conditions. I start with the exhaust stroke and then move on to intake,compression and expansion strokes.During the run,just at the beginning of the compression stroke i get the foll. error:

Error#076 Negative densities at more than 100 cells.Run stopped.

Does anyone know the cause of this error and how to resolve the same? thanx in advance

Mihir.

PS: I'm using ideal f(T,P) for density.

Re: negative densities.
 

hi mihir, since u r using ideal gas f(t,p) for density..density is also variable.so what would be happening in ur case due to very high relaxation factor for density at any iteration the density would be coming negative. decrease the relaxation factor for density until u did not get these error.u can do this also decreasing both pressure and density factor at a time. let me inform if u get out the problem. nikhil

Re: negative densities.
 

HI Nikhil, thanx for replying.I've already played with the relaxation factors with no result.could it be a problem with the mesh? I have used the vc3dgen command in the cylindrical co-ordinate system to generate the cylinder cells.Hence the central cells are all prismatic.But STAR-CD considers prismatic cells as hexa cells collapsed along a face.So could it be that these cells are treated as cells with a high aspect ratio?Let me know if u have some info on that front. Thanx again.

Mihir.

Re: negative densities.
 

Have a look at the statements posted here in former times

Re: negative densities.
 

Also, try using finer time steps -be mindful of your Courant number. This error could happen too when joining back previously excluded cells regions. There are a couple of articles on ICE sims on www.adapco-online.com.