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Heat Release Rate in fireFoam

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Old   June 20, 2019, 08:34
Default Heat Release Rate in fireFoam
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Ingo Riess
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I try to model a methane fire in a tunnel with longitudinal air flow.

- I use OpenFoam v1812
- The simulation is based on the fireFoam tutorial smallPoolFire3D
- The longitudinal flow is modelled as a mass flow rate on the inlet.
- The fire source is modelled as another inlet of methan.
- The heat release rate is calculated from the methane mass flow rate.

I have some difficulties with the boundary conditions, see my other question.

This question is about the reading of the heat release rate in fireFoam and in ParaView.

I read the heat release rate HRR from the following code in controlDict:
Code:
functions
{
    HRR
    {
        type            volFieldValue;
        functionObjectLibs ("libfieldFunctionObjects.so");
	log             true;
	writeControl    timeStep;
	writeInterval   1;
	writeFields     false;
	regionType      all;
        operation       volIntegrate;
        enabled         true;
        fields
        (
            Qdot
        );
    }
}
The code gives me a total heat release rate of ~60 MW.

In ParaView (filters>data analysis>integrate variables:Qdot), I find a total heat release rate of ~60 MW.

The methane flowrate of 0.0204 kg/s (BC) should give me a heat release rate of 1MW.

I compared the flow field and the temperature distribution in the tunnel with empirical models (e.g. Austrian tunnel ventilation design code) and from the temperature data, I'd estimate the HRR in the tunnel at 14 MW.

What am I doing wrong? I'd appreciate any help you could give me.

Last edited by ingraban; July 4, 2019 at 03:34.
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Old   July 12, 2019, 03:29
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By now, I think the code works just fine and there were other issues with the setup of the model. For future reference, there is a warning using this code. The line
Code:
        functionObjectLibs ("libfieldFunctionObjects.so");
should be replaced by
Code:
        libs            ("libfieldFunctionObjects.so");
Take care
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Old   September 23, 2022, 19:16
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Hi ingraban, did you manage to get correct HRR in comparison to mass flow rate (inlet boundary condition)?


If yes, how did you manage?



Thanks in advance!
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Old   October 6, 2022, 11:41
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Ingo Riess
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Hi
No, I did not get the heat-release rate according to the specified mass-flow. Usually, the effective heat release rate was higher. I assume, some turbulence or flow eddies at the inlet boundary condition lead to additional fuel-supply. For small flow rates I had to reduce the area of the fuel inlet.
All the best
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