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flowRateInletVelocity compressible

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Old   April 15, 2010, 12:12
Default flowRateInletVelocity compressible
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Oli
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Hello world!

I have a question about the unit of the inlet boundary flowRateInletVelocity.

When using an incompressible solver like simpleFoam, the flowRate is given in [ m/s ].

Which unit is given when using a compressible solver, for example buoyantPisoFoam?
Is is it still [m/s] or then [kg/s] ?


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Old   April 15, 2010, 12:44
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Cedric Van Holsbeke
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Your question is answered in the following part of flowRateInletVelocityFvPatchVectorField.C:

Code:
00129     if (phi.dimensions() == dimVelocity*dimArea)
00130     {
00131         // volumetric flow-rate
00132         operator==(n*avgU);
00133     }
00134     else if (phi.dimensions() == dimDensity*dimVelocity*dimArea)
00135     {
00136         const fvPatchField<scalar>& rhop =
00137             patch().lookupPatchField<volScalarField, scalar>(rhoName_);
00138 
00139         // mass flow-rate
00140         operator==(n*avgU/rhop);
00141     }
If the dimension of phi is in m^3/s, the value of flowRateInletVelocity will be a volumetric flow rate in m^3/s. If the dimension of phi is in kg/s, the value of flowRateInletVelocity will be a mass flow rate in kg/s. I think this is indeed the difference between an incompressible and a compressible solver, but I'm not sure.
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Old   April 16, 2010, 03:56
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Cedric Van Holsbeke
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I was indeed correct:
Incompressible solver: phi is in m^3/s --> flowRateInletVelocity is in m^3/s
Compressible solver: phi is in kg/s --> flowRateInletVelocity is in kg/s
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Old   August 27, 2010, 05:31
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I didnt get this concept. How i suppose to give the mass flow rate value, for the same case, when i am solving with incompressible solver and with compresible solver??? Say i have a mass flow rate of 5kg/s through an inlet. can anyone elaborate please???
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Old   August 27, 2010, 05:42
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Cedric Van Holsbeke
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Assuming that you use a fluid with the density of water (rho = 1000 kg/m) and you want to achieve a mass flow rate of 5kg/s, you will have to fill in this value for the flowRate:
  1. Incompressible solver: flowRate 0.005 (= massflow/rho = (kg/s)/(kg/m) = m/s)
  2. Compressible solver: flowRate 5 (= massflow = kg/s)
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Old   August 27, 2010, 05:56
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Oh..gotcha...

Thanks Cedric for the quick reply..Have a good day..
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