solver problems at extreme low velocities

matthias

Dear all, I am working on CFX to model a laminar flow through a micro channel with a diameter of 1 mm. Because of the narrow channel and a high viscosity the velocity is very low (<0.02m/s). I am working with Reynolds numbers about one. For Reynolds numbers higher then 3, I had no problems achieving convergence. By decreasing the velocity, the RMS values aren't running below a value of 1e^-4. This problem seems to be grid independent. I increased the number of elements with factor 80 and still had the same problems. Because of the solution of those not converged runs showed arbitrary behaviour of the flow field I think altering the convergence criteria is not a good idea. Maybe someone has an idea how I can handle this problem with CFX. Or is there any other possibility to solve it with a different method (e.g. DNS)? Thanks

Matthias