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Hi
I am working on internal flows like duct or intake flows in STARCCM+ and got handicap or stuck with boundary conditions. It would great help if someone can provide some suggestions. I am simulating a body with an inlet duct. The body is placed in Pressure far-field domain (see picture below "inlet.jpg"). Flow can enter in duct on its own but there is a pressure outlet boundary condition at duct exit to control mass flow rate. I have set reference pressure for simulation to 101325 Pa For any pressure outlet value, there is a specific mass flow rate passing through pressure outlet. For example, if 5000 pa static pressure is applied at duct outlet, the pressure is achieved and required mass-flow is also achieved. Then pressure is increased 10000 the mass-flow reduces and required values are achieved. Then static pressure is increased to 15000 and required static pressure and mass flow is achieved at duct exit. But if pressure is increased from this point on-wards, no matter what, the specified pressure is not achieved and mass flow also got stuck to a fix point. The details can be seen below: Press Val Spec Press Val achvd Mas Flo rate achvd Status 5000 Pa 5000 Pa 20 kg/s Easily Converged 10000 10000 18 Easily Converged 15000 15000 16 Easily Converged 20000 18000 14 Req. values not achieved 25000 18000 14 Req. values not achieved 30000 18000 14 Req. values not achieved From the point onwards where pressure got stuck, I have tried few changes but not succeeded yet. Summary Changed "Pressure outlet BC" with fixed pressure to "Pressure outlet BC" with target mass-flow rate option ............... result: specified mass flow rate, pressures and velocities are highly oscillatory in duct..... no steady solution achieved Changed "Pressure outlet BC" with fixed pressure to "Outlet BC" with fixed mass-flow rate option ............... result: specified mass flow rate is fixed on specified value but pressures and velocities are highly oscillatory ..... no steady solution achieved Changed "Pressure outlet BC" with fixed pressure to "Pressure outlet BC" with avg face pressure option ............... result: specified mass flow rate, pressures and velocities are highly oscillatory ..... no steady solution achieved I also tried to Change "Pressure outlet BC" with fixed velocity option ............... result: velocity is fixed but mass flow rate and pressures are highly oscillatory ..... no steady solution achieved Only little progress is made with tweaking with back pressure Tweaked with Outlet "Back Pressure" from "Enviornmental" option to "Static Pressure" Option ............... result: specified mass flow rate, pressures and velocities achieved ..... but only for limited number of simulations .... summary below: Press Val Spec Press Val achvd Mas Flo rate achvd Status 5000 Pa 5000 Pa 20 kg/s Easily Converged 10000 10000 18 Easily Converged 15000 15000 16 Easily Converged 20000 20000 12 Easily Converged 25000 22000 11 Req. values not achieved 30000 22000 11 Req. values not achieved I can't find any option or limiting factor that why my specified pressures or velocities or mass flow rates are not achieved in form of steady state solution after a certain limiting value of pressure. Any possible solutions to this problem, Also see the setup picture attached ... "inlet.jpg". Any help in this regard is much appreciated. |
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