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Outlet boundary condition for compressible nozzle flows |
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July 12, 2016, 09:40 |
Outlet boundary condition for compressible nozzle flows
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Bruno Blais
Join Date: Sep 2013
Location: Canada
Posts: 64
Rep Power: 13 |
Hello everyone,
I am currently trying to simulate a nozzle with an exit section (see attached figure). The configuration is very simple, it's a nozzle with a convergent then a constant section barrel then it exits the barrel. After that, there is a large empty zone where the jet exits before leaving with the outlet boundary. I have been trying to solve the flow with both pisoCentralFoam and sonicFoam, but to no avail. At the inlet I impose pressure boundary condition with zeroGradient for the velocity. Pressure boundary is 1.4 MPA. The bottom is a symmetry boundary condition. At the non-reflective outlet I impose waveTransmissive boundary conditions for the pressure. For example : Code:
outlet { type waveTransmissive value uniform 1e5; //important for correct I/O field p; //the name of the field that we are working on gamma 1.4; //the ratio of specific heats phi phi; //the name of the volumetric flux field ( or if you use the mass flux phi, it will be divided by rho) rho rho; //the name of the density field psi thermo:psi; //the name of the field that is the deriv. of density with respect to pressure lInf 0.1; //a measure of how far away the far-field condition should be fieldInf 1e5; //the far-field value to be applied to pe; } Anyway, I get decent results within the nozzle, however, the pressure profile and velocity profile outside the nozzle are very poor. There is a pressure accumulation at the bottom right corner of the simulation, and therefore a large velocity appears going upward very close to the outlet boundary. I have tried many alternative, but I cannot find a solution to my issue. I was wondering if any of you had any idea? I am sure it is relative somehow to my outlet boundary conditions, but I don't know. My only leftover option right now is that I think that maybe the symmetry boundary condition at the bottom is too much of a large constraint and this is what makes the upward velocity appear, but this is really all I have. Thanks! BB |
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