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weird pressure and turbulent intensity when using |
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#1 |
New Member
Join Date: Aug 2017
Posts: 9
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hello
I have a big trouble when I using timeVaryingMappedFixedValue.in the /constant/boundayData/inlet/,I put 30000 directory and every directry only contain the U.the deltaT of the inflowData is 0.0001,and my calculating deltaT is also 0.0001,the simulation time is 3 seconds.That means I don't need time interpolation in the inflow data.and in my "points" file,I set 156*56points,so I think every grid on the inlet face can get the data. my case is a 3d rectangle ,and in my uploading picture,the left side in the inlet and rightside is the outlet. When I check the result I find the pressure field around the inlet boundary is very weird (looks like discontinuous).and the turbulent intensity is obviouly less than the inflow date.But actually the timeVaryingMappedFixedValue does works. I upload my picture of my pressure field. Does anyone can help me,I already struggle with this trouble for 1 month.: And I have such question. 1. does timeVaryingMappedFixedValue can give a smooth inflow ?what's meaning of the "mapped"? ![]() 2.do I have to add the "p" file when I use timeVaryingMappedFixedValue? |
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#2 |
Senior Member
Timofey Mukha
Join Date: Mar 2012
Location: Stockholm, Sweden
Posts: 119
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1. Pressure fluctuations near the inlet is a common problem with inflow generation. It is caused by the fact that the solver attempts to enforce a divergence-free velocity field.
Mapped reffers to the fact that the bc can interpolate in space from the points where u provide the data to the face centres of the patch. 2. No, if u provide velocity data the pressure should be set to zero gradient. |
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#3 |
New Member
Join Date: Aug 2017
Posts: 9
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Dear tiam
Thank your replying and sorry for my reply late. In my case I use thetimeVaryingMappedFixedValue BC .If I use tetra unstructure mesh,the turbulent intensity look likes be tweaked and become strange.but when I use hex structure mesh grid system which parallel with inflow direction,the turbulent intensity can be kept very well,Do you know why such condition will appear? Sincerely Tang |
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#4 |
Senior Member
Uwe Pilz
Join Date: Feb 2017
Location: Leipzig, Germany
Posts: 744
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Unstructured meshes are most often triangular ones. You have a linear approach here, which is very diffusive. I don't recommend triangular meshes for serious calculations.
Hex meshes have a quadratic approach and are much less diffusive. It is much more expansive to get a local mesh refining with hex meshes, however.
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Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950) |
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#5 |
New Member
Join Date: Aug 2017
Posts: 9
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Dear Uwe Pilz
Thank your replying~! |
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