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Unexpected difference between velocity / mass-flow inlet |
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#1 |
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Hello,
I am modeling a 3D incompressible inviscid airflow in a system. It has 1 velocity inlet and a number of outflow outlets. It converges fine. Then I check the mass flux via inlet: let's say it is M_dot and switch velocity inlet to mass-flow inlet, request a flux equal to M_dot. Case loses convergence right away and can't converge properly anymore. I don't understand why. Nothing really has changed, except the inlet type. Where am I going wrong? Thank you for your thoughts. |
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#2 |
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Maxime Perelli
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try to switch from outflow to pressure outlet.
I always heard that combination velocity-inlet / pressure-outlet was more stable than mass-flow-inlet / pressure-outlet. Don't ask me why...
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#3 |
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-mAx-, thank you for your reply and for the time you dedicate in helping others in this forum
I tried this, but there is a problem. How do I set the pressures? My goal is to switch the whole thing to compressible flow. But velocity inlet/outflows do not work with pressure. I cannot make the transition... |
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#4 |
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Maxime Perelli
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I don't understand what you mean with transition.
Set your outlet with Pressure-Outlet Boundary Condition. Set your pressure with 0 Pa (outlet free)
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#5 |
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My system has a number of outlets. Compressible simulation is hard to converge. This is why I do incompressible first and try to find out the pressures on all terminals.
Once this is done, I can retry running compressible calculation with the new pressures. |
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#6 |
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Maxime Perelli
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So you have number of outlets, but you don't know neither their pressure, nor their massfow?
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#7 |
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that is correct
![]() I only know their approximate massflow percentages (e.g. parts of the mass entering the system) |
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#8 |
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Maxime Perelli
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then try to work with pressure-outlet and enable target massflow option, with giving approximate massflow
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#9 |
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to be honest, whenever I have tried enabling target mass flow on pressure outlets, it hardly ever works
![]() It didn't work in this case either But it works with velocity inlet/outflow exits. I am trying to figure out how to use this successful calculation and set up the exits as pressure outlets |
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