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March 19, 2022, 08:06 |
OpenFoam Transient Wind Velocity Problems
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#1 |
New Member
Zach Tolmie
Join Date: Mar 2022
Posts: 1
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Hello all, I'm quite new to OpenFoam, so in all likelihood this will be a stupid mistake on my part!
I am attempting to run a transient simulation (rhoreactingbuoyantfoam) of a gas leak, with parabolic wind conditions. I've tried mesh refinement and running with uniform wind velocity and the same thing also happens. As I increase the timestep, the velocity past the inlet increases exponentially, to supersonic speeds. This region lasts for about 20 meters, after which the velocity is flowing in the negative direction, or is close to zero. I've attached the files for U, P and p_rgh. Any help would be much appreciated! Thanks, Zach |
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March 19, 2022, 10:13 |
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#2 |
Senior Member
Uwe Pilz
Join Date: Feb 2017
Location: Leipzig, Germany
Posts: 744
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From my experience, buoyancy and addition free stream does not work very well and gib unrealistic high velocity at points where the buoyancy ends (downstream).
I have decoupled the physics for my application. May be there is another was. I would be interested reading a solution.
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Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950) |
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March 20, 2022, 00:57 |
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#3 | |
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Join Date: Jun 2019
Posts: 41
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Quote:
Hello. What do you mean by «I have decoupled the physics » ? You don't add the buyoyancy term to the momentum NavierStokes Equation ?
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« Debugging is what CFD is about. 5 minutes to modify your code, 5 months to find why it does not work anymore. » |
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March 20, 2022, 01:37 |
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#4 |
Senior Member
Uwe Pilz
Join Date: Feb 2017
Location: Leipzig, Germany
Posts: 744
Rep Power: 15 |
That is not easy. But in principle, I solved the buoyancy alone and used the result as boundary conditions for a fress stream simulation.
You have to decide where the flow is buoyancy dominated. Of course you intrduce some error in the region where both, buoyancy and free stream, act. But you get a result at all. It was a few years ago and I don't know every thing I tried. But at least a used a "mixing area" where I added the buoyancy effects (beyond the buoyancy limit) to the free stream simualtion.
__________________
Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950) |
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