# flowRateInletVelocity compressible

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 April 15, 2010, 12:12 flowRateInletVelocity compressible #1 New Member   Oli Join Date: Apr 2009 Posts: 27 Rep Power: 10 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 [ m³/s ]. Which unit is given when using a compressible solver, for example buoyantPisoFoam? Is is it still [m³/s] or then [kg/s] ? Best Regards

 April 15, 2010, 12:44 #2 Member   Cedric Van Holsbeke Join Date: Dec 2009 Location: Belgium Posts: 81 Rep Power: 10 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& rhop = 00137 patch().lookupPatchField(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.

 April 16, 2010, 03:56 #3 Member   Cedric Van Holsbeke Join Date: Dec 2009 Location: Belgium Posts: 81 Rep Power: 10 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 cutter, calim_cfd, pfhan and 4 others like this.

 August 27, 2010, 05:31 #4 Senior Member   Nilesh Rane Join Date: Apr 2010 Posts: 122 Rep Power: 9 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??? __________________ Imagination is more important than knowledge..

 August 27, 2010, 05:42 #5 Member   Cedric Van Holsbeke Join Date: Dec 2009 Location: Belgium Posts: 81 Rep Power: 10 Assuming that you use a fluid with the density of water (rho = 1000 kg/m³) and you want to achieve a mass flow rate of 5kg/s, you will have to fill in this value for the flowRate: Incompressible solver: flowRate 0.005 (= massflow/rho = (kg/s)/(kg/m³) = m³/s) Compressible solver: flowRate 5 (= massflow = kg/s)

 August 27, 2010, 05:56 #6 Senior Member   Nilesh Rane Join Date: Apr 2010 Posts: 122 Rep Power: 9 Oh..gotcha... Thanks Cedric for the quick reply..Have a good day.. __________________ Imagination is more important than knowledge..

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