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Wrong forces coming from forces function object in controlDict

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Old   April 13, 2016, 09:07
Exclamation Wrong forces coming from forces function object in controlDict
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I am simulating turbulent flow through a straight pipe (0.254 m in diameter) with pimpleFoam and a standard k-epsilon model. On the invert of the pipe I have placed a number of protruding "baffles" from geometries within snappyHexMesh. The flow through the pipe is 0.035 m^3/s.

I am interested in calculating the pressure drop over the baffled section with an energy approach and also with a momentum based force balance approach. So far, the energy approach has given the correct pressure drop between the upstream and downstream section ((p1avg*rho-p2avg*rho)/(rho*g), but the forces coming from the forces function are much lower than they should be (by about half) and consequently the momentum approach is not working. Also the force due to shear stress on the wall of the pipe is lower than it should be.

The fact that the energy approach is working gives me confidence in model and also leads me to believe that I am somehow incorrectly using the forces function object.

I have been breaking my head over this for the past few days and figured I have exhausted all the leads I could find in other related threads. It would make my day if somebody could help me out.

Here is my forces function object entry in controlDict, I am fairly confident I have entered everything correctly:

type forces;
functionObjectLibs ("");
patches (baffles);
rhoName rhoInf;
pName p;
UName U;
CofR (0 0 0);
rhoInf 1000;
name forces;
uitype forces;
outputControl outputTime;
outputInterval 1;
format ascii;

Also, the baffles are not a continuous geometry - instead the patch is composed of 15 distinct 0.038x0.038*0.01 separated from each other by 0.15 m along the x-axis (main flow direction). Could this have something to do with the problem I am seeing?

Thank you for your help!
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forces, pressure losses, turbulent flow

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