I am modeling a duct flow with one inlet and four outlets. The duct cross section is non circular and very irregualr. The obejective of the simulation is to predict the mass flow distribution at the outlets for a given mass inlet. The flow is incompressible and turbulent. I am imposing a velocity inlet and a pressure outlet ( outlets were placed 10 diameters downstream to avoid reversed flow).
I was able to obtain a solution where the residuals reduced to 1.e-5 smoothly, but the mass flow rates at the outlets were oscillating. In other words, outlet mass flow rates are a function of iteration. The solution I got shows that there are a lot of secondary flows and a swirl flow at the outlets ( physical outlets). This is somewhat similar to the "swirl back flow" message posted by Jonas Larsson.
I am using Fluent solver and tried different boundary conditions and different turbulent models with no success. Please advice .....
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