Calculate Mass Flowrate and Mass Flow Averaged Total Pressure at inlet and outlet
 

Hi Foamers,

I have simulated centrifugal pump using OpenFoam 2.4.0 and working on post processing of it.

I have to calculate Mass Flow Rate at Inlet and outlet patches. Also I have to calculate the Mass Flow averaged Total Pressure at inlet and Outlet patches.

I have some questions though:

1) I have used patchIntegrate phi to evaluate the Mass Flow Rate at inlet and outlet. I am getting a reasonable value at outlet patch but getting value zero at inlet patch ( but inlet velocity given is ( 0 0 4.5 ) ). I dont understand why its zero.

2) What is the difference between patchAveragie and patchIntegrate ? I have used patchAverage phi but openfoam says its an error and says Only possible to average volfields but phi is surfaceScalarField

3) How the total pressure be attained and perform mass flow averaging on the inlet and outlet patches.

I have gone through many forums but could not get a clear answer. I am new to CFD and using Openfoam.

Any help regarding this would be great :)

Thanks and Best Regards

Any help foamers !!

Any suggestions or guidance is welcomed :)

Quick answers:
Without an example case, I can't even guess the reason why it's zero. Please read and follow: https://www.cfd-online.com/Forums/op...-get-help.html

patchAverage is essentially the result of dividing the integration on the surface of a patch by the total area of the patch. It only works with volume fields, because it was coded to only work with volume fields.


Function objects. Read the OpenFOAM User Guide on how to use them. Then check https://cpp.openfoam.org -> "FunctionObjects" (in older pages it was "Post-Processing") near the bottom of the page -> then:

• Utility function objects -> pressureTools
• Field function objects -> faceSource

I believe there are already a few examples on this already here on the forum.

Thank you. That helped me.

Any clue how to do mass flow averaging? I am using function objects but they do only area averaging

Quick answer: Field function objects -> faceSource -> weightedAverage
The weight field should be rhoPhi. Partial example can be found in the tutorial "multiphase/interFoam/ras/waterChannel", the remaining configuration is shown in in the code documentation I mentioned before, namely the link to sourceforge.net.

I use patchAverage phi successfully ，which one should I to calculate mass flow between patchaverage and patchIntegrate？

Thank you.

Quick answer: mass flow rate is calculated by using the "sum" operation on the "phi" field instead of the average one... see surfaceFieldValue: https://cpp.openfoam.org/v5/classFoa...e.html#details

Hi, 'patchIntegrate(phi,name=inlet)' will give you (Integral phi *dA ), whereas patchAverage will give you (integral phi*dA)/A. As per OpenFoam documentation the unit of phi is kg/s (per face?) for compressible solvers and m3/s (per face?) for incompressible. The function 'flowRatePatch(phi,name=inlet)' gives the mass flow rate through a patch as it sums over all the faces of a patch. Hope it helps.