dear all

i am working with ic engine transient analysis ....and getting following error

*** ERROR #076 *** NEGATIVE DENSITIES FOUND AT MORE THAN 100 CELLS. RUN STOPPED .....

can any one give the solution to get rid of this error .....

THANKS IN ADVANCE

use low relaxation factor

As I know there are many reasons to occur 'Negative densitys...'

In compressible flow, the density are calculated by the pressure field which is obtained by velocity field. And the pressure is linked with the temperature and density using equation of state(i.e. P=rho*R*T). Therefore "Negative density" may occurs due to the unreasonable pressure field. So check the time step with respect to Courant Number(if transient), or diffusion length> convection length.

Also if you have scalar source function in your code(sorsca.f), check whether the mass fraction of each scalar exceed '1'. These unphysical situation may occurs the unreasonable flow field, density field.

So,if I really found that the mass fraction of the scalar exceed 1, what can I do to fix this problem?

As I know, the reason that mass fraction exceeds '1' may be that scalar mass generated during one time step exceed the amount which can be generted.

for example.

if we are using ION(scalar1), ELE(scalar2) and background gas(N2)

N2 is ionized then N2 --> N2+(ION) + e-(ELEctron)

The scalar mass rate(S1P in sorsca.f) generated during time step is estimated with the follwing:

if( S1P > (1.0-SCALAR(1)-SCALAR(2))*DEN/DT ) then S1P = (1.0-SCALAR(1)-SCALAR(2))*DEN/DT endif ++++++++++++++++++++++++++++++++++++++++++++++++++ +

I am handling that problem like this.

Check the able scalar mass for each scalar at any time step.