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Adding pressure and temperature sources instead of energy

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Old   October 23, 2016, 04:07
Default Adding pressure and temperature sources instead of energy
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rae
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I have an intense thermal energy source and am concerned solving the hydrodynamic equations before the energy and turbulence equations. I think it would be better to add temperature and pressure to source volume elements directly (based on state equation) and then the solver is ahead when working out the hydrodynamic equations first (and probably end up with less solver divergence issues on energy and turbulence). I have already tried iterating on p_mass after energy but ...

Is there a way to change the static pressure and temperature variables at the end of each time step, i.e. ready for the next? I know how to read the variables but can I write to them?

Thanks.
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Old   October 23, 2016, 05:29
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Glenn Horrocks
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No, you cannot do this. Besides, the solver cannot converge if you go in there and change values.

CFX is a coupled solver so will get the coupling between temperature and flow better than most CFD codes. So just use it with the default solver setup and it should work fine.
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Old   October 23, 2016, 20:05
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Thanks for the info Glenn. I suppose after the first iteration within the timestep the pressure and temperature variables are adjusted for the energy source anyway. Just a final question you might help with, when a max temperature is set with air as an ideal gas, what happens when the limit would otherwise be exceeded? Is the excess internal energy just dumped or is it translated into pressure by the state equation relationship?
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Old   October 24, 2016, 02:31
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I suppose after the first iteration within the timestep the pressure and temperature variables are adjusted for the energy source anyway.
That is exactly right. Note "Coupling" refers to how the pressure and momentum equations (also energy and others if relevant) are linked such that the final result satisfies both sets of equations.

If the solver hits an artificial limit on values then the solver is unlikely to converge. If the solver thinks a region of really hot gas exists you cannot stop it by defining an artificial limit. If the region of hot gas is not real then you have to find where in your simulation setup the hot gas is being created and fix that.
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