Setting Pressure outlet boundary for simulation of Radial impeller
I am using a C code for simulation of flow field of an radial impeller. The code is an Finite Volume Solver using Simplex Algorithm. The inlet boundary condition is set as mass flow inlet and outlet is using Neumann boundary condition. I am using Laminar and Incompressible flow,Collocated Grid with the option of doing both steady and unsteady simulations.Presently i am using unsteady simulation and i want to effectually change the outlet Boundary condition so that i have a pressure outlet boundary . so i have tried setting it but the flow field changes and it seems giving wrong results. I have tried working some way out but its seems unfruitful. I hope many among you will have some suggestions.
To be honest, I know little about CFD mathematics models. But one thing I learn is, 'open' or 'pressure' kind of outlet may have quite a problem of back flow, convergence and the length of the outlet pipe..
So I gave up thinking so, and put a velocity / flowrate on the outlet, which has an equal amout of flow rate out as the flow rate in... So the model will become like 'blow and suck' pipe thing.
I have not expected any comparison that it will be better or worst in this way, but at least the convergence of the model is not a problem anymore.
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