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setting OUTLET flow rate equal to INLET flow rate

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Old   March 22, 2018, 06:33
Default setting OUTLET flow rate equal to INLET flow rate
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Suffolk
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Hi all,

I am currently simulating a Jet Entrainment case and have a question regarding boundary conditions.

I will be prescribing the Jet Outlet boundary condition with various profiles and values—for instance, initially a uniform profile value of various flow rates, then a parabolic profile, then a ramp profile with different maximum velocities, then a Turbulence generator inlet.

The overall flow rate (phi) will change with each simulation.

The Jet Inlet (Jet collection is probably a more suitable name) is a patch that I need to calculate the following:

1. amount of ambient heat collected due to the jet entrainment
2. amount of species mass collected due to the jet entrainment
3. velocity profile

Now, this patch must have the exact same total flow rate as the inlet—at all times.

I have seen a few posts on here coving similar things using GroovyBC but I can't see why that is necessary.

Below is the boundary condition that I am currently using.

Code:
    
Outlet
 {
        type   flowRateInletVelocity;
        volumetricFlowRate constant -0.001648068;
        extrapolateProfile true;
        value           uniform (0 0 0);
    }
Now I am using the "extrapolateProfile true" because I don't know the velocity profile and it is certainly not uniform—so I need to calculate that from extrapolating from the neighboring cells.

I want to keep this boundary condition almost exactly as it is. But I would like to change this line:

Code:
volumetricFlowRate constant -0.001648068;
to something like this:

volumetricFlowRate Phi(Inlet) ;

so that the outlet flow rate is connected to the inlet flow rate. So any changes to the Inlet profile will automatically be updated to the Outlet.

I have an ambient boundary condition that is set to P_rgh=0. Far away from the Jet. Just in case anyone was going to ask where I am defining the pressure.

I would really appreciate any help! I have a little experience with the dynamic code boundary conditions. But I don't really want to re-write the BC as the flowRateInletVelocity BC already is doing 95% of what I need!

Best Regards,

Shaun
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boudary condition, dynamic boundary, flow rate, jet, openfoam

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