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Correct p_rgh boundary conditions to include buoyancy

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Old   May 8, 2023, 18:47
Default Correct p_rgh boundary conditions to include buoyancy
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Daniel Thomas
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I've not been able to include the effects of buoyancy in my 2D simulations of a counterflow flame. I'm using the EBI-DNS solver, which is based on the rhoReactingBuoyantFoam solver in OpenFOAM v1712. Simulations all run as expected, except that I can't produce any buoyancy effects, even in conditions where these should be evident and with exaggerated gravitational force.

I'm using a wedge domain as shown below, and have tried several boundary conditions for the 3 flow boundaries (air inlet, fuel inlet, and outlet). Currently they are waveTransmissive for the 0/p_rgh (as below), and calculated for 0/p. I am trying it with and without buoyancy by modifying the gravitational force defined in the file /constant/g. Are these boundary conditions appropriate, or is there something else that could be wrong? (See the attached p and p_rgh files.)

Thanks for any suggestions,


dimensions      [1 -1 -2 0 0 0 0];

internalField   uniform 101325;

        type            waveTransmissive;  
        psi             thermo:psi;        
        gamma           1.3;               // Ratio of specific heats 
        fieldInf        101325;            // The far-field value to be applied to p
        lInf            0.1;               // A measure of how far away the far-field condition should be
        value           $internalField;  
Attached Images
File Type: png Counterflow - OpenFOAM domain.png (11.4 KB, 2 views)
Attached Files
File Type: txt p_rgh.orig.txt (2.8 KB, 1 views)
File Type: txt p.orig.txt (1.4 KB, 0 views)
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Old   May 24, 2023, 16:01
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Daniel Thomas
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I'm still working on this, and would be grateful for any suggestions. I saw the recent helpful reply by Yann in this post. Based discussions here and other example code, I'm using:
  • 0/U - fixedValue for both inlets and inletOutlet for the radial outlet. (In the corresponding experiment, flows are metered in at a constant flow rate.)
  • 0/p - calculated for both inlets and the outlet. (Standard for OpenFOAM with buoyancy.)
  • 0/p_rgh - I assume this is where I'm getting something wrong. I've tried fixedFluxPressure, zeroGradient, and waveTransmissive as described below.

The code runs fine with a waveTransmissive BC for the outlet. But for all these solutions, both the resulting p and p_rgh fields are uniform accross the domain. For the low velocity flows and exaggerated graviational force I'm using, I should see an upward shift in the flame position, but results are still identical regardless of the applied gravitational field. The attached plot shows the flame position with the temperature color plot, and a flow vector overlay.

It seems like a zeroGradient BC would be appropriate for the vertical outlet, to allow pressure to vary hydrostatically along the boundary. However, I run into numerical issues when trying this (and waveTransmissive or fixedFluxPressure for the inlets). And, as expected, I also can't get a solution when I try fix the pressure at an inlet with prghPressure.

Any suggestions for inlet p_rgh boundary conditions that would allow me to use the zeroGradient outlet BC? Or is there another BC that would allow for hydrostatic pressure variation along this vertical outlet boundary?

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File Type: jpg counterflow_XH2-70_a-100_T_and_U.jpg (94.3 KB, 5 views)
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boundary conditions, bouyancy, p_rgh, rhoreactingbuoyantfoam

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