Hi!

Has anyone observed the numerical instability over the swirling vanes. What we have is the flow over a set of vanes. We have pressure inlets and one pressure outlet. What we are observing is the mass flow rate through the pressure outlet is oscillating in a sinusoidal fashion.

Has anyone come across this kind of situation and has any comments/suggestions. We have tried with lowering the under relaxation factors. Even to a small number like 0.001, the mass flow rate is still sinusoidal.

Some strongly swirling flows can have their vortex cores precessing - the vortex axis undulates in a snaky and unsteady fashion. Some advanced RANS models can often capture this phenomenon showing a limit cycle-like behavior of the residuals or oscillations in the solutions fields even in steady simulations. So, what you're witnessing may not be "numerical instability" but probably a physical one.

where is your pressure oulet located? is it at appropiate location?

pressure oulet is about an inch downstream from the end of the end of the vane.