uds errors

major

hello everyone: My case is about calculating 2D tubulent flow and a scalar equation. In the scalar equation, the source term=const* gradient(scalar) in y axis; one of the wall boundary condition: flux= const* scalr on the wall; other wall boundary condition: zero flux velocity inlet and out flow boundary condition were used. When the const equal to 1.11e-03, I can obtain the reasonable results. But when the const increase, such as const equal to 1.15e-03, when iterate 20 times, the min. scalar becomes negative and can not continue iterate. I don't know the reason.

Thanks for every advice.

major