negative species concentration again

Andrew Garrard

I asked this question before, but I didn't get an answer that I was happy with and it got washed down the list of posts, so I will post it again.

I am building my own species concentration model using a UDS. The rate of reaction is proportional to the value of the species concentration. If the initialisation conditions are such that reaction rate is sufficiently fast to cause my UDS (species concentration) to go negative after the first iteration. In the fluent species concentration model with a fast reaction rate the species concentration will NEVER go negative. Dose anyone know how fluent control this?