# simpleFoam body forces wedge BC interation!

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 March 27, 2017, 13:22 simpleFoam body forces wedge BC interation! #1 Member   OpenFoam Join Date: Jun 2016 Posts: 82 Rep Power: 8 Hi All, I am trying to manipulate a volume source term that was add to the simpleFoam solver to simulate the flow over a horizontal axis wind turbine. The governing equations used in the code is as follows; The elementary lift and drag forces on the blade section are given by: eq1.jpg The axial and circumferential forces are; eq2.jpg The circumferential force can be further analyzed to the y and z directions of the Cartesian grid: eq3.jpg If the rotor is composed by B blades, the forces per unit surface will be; eq4.jpg The code was tested and validated successfully and all simulations were done in 3D. My aim is to apply the boundary condition wedge i.e. axisymmertric simulations to save some computational cost. However, the volume force terms programmed in the source code using the above equation are in 3D. I am currently having an issue on which source term should be excluded to be able to make it axisymmetric. Does anyone understand my question here? Can anyone help or suggest any document might help me to get it to work in Axisymmetric? Thank you again for your time.

 March 27, 2017, 14:16 #2 Senior Member     Uwe Pilz Join Date: Feb 2017 Location: Leipzig, Germany Posts: 742 Rep Power: 14 My 2C: Without changing anything at the simulation you may transform your problem into an axialsymmetric *manually*, with replacing the x coordinate by log(r/r_i). The coefficents are not correct for this geometry. You may transform the coefficients, or - may be simpler - export the velocities and forces and re-transform them to x/y. In this retransformed system all stream values are at the right place and the coefficients may calculated bu numerical integration / simple summation. __________________ Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950) Last edited by piu58; March 28, 2017 at 02:57.

March 27, 2017, 14:38
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Hello Pilz,

Thank you for the kind clarifications and help. I don't fully understand how would I replace the x-coordinates by log(r/r_i) .

Quote:
 Originally Posted by piu58 Without changing anything at the simulation you may transform your problem into an axialsymmetric *manually*, with replacing the x coordinate by log(r/r_i).
I definitely agree with you that the coefficients are not correct since the wedge boundary condition requires 5 degree extrusion.

Quote:
 Originally Posted by piu58 The coefficents are not correct for this geometry.
Unclear how would I transform them if they are already incorrect from the axisymmertic simulations?
Quote:
 Originally Posted by piu58 export the velocities and forces and re-transform them to x/y. In this retransformed system all stream values are at the right place and the coefficients may calculated bu numerical integration / simple summation.
Thanks again.

 March 27, 2017, 15:04 #4 Member   OpenFoam Join Date: Jun 2016 Posts: 82 Rep Power: 8 To be more specific, here are the results of the forces and velocity for both simulations i.e. Axisymmetric and 3D results. Axi.tar.gz 3Dsimulation.tar.gz Thanks in advance, Last edited by CFD-Lover; March 28, 2017 at 08:44.

 March 28, 2017, 08:57 #5 Member   OpenFoam Join Date: Jun 2016 Posts: 82 Rep Power: 8 It seems that no one in the CFD-Online knows how the wedge BC works.

 April 1, 2017, 01:43 #6 Senior Member     Uwe Pilz Join Date: Feb 2017 Location: Leipzig, Germany Posts: 742 Rep Power: 14 I look at your simulation the next few days and try to find out something. Please give me some time for that. CFD-Lover likes this. __________________ Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)

 April 2, 2017, 01:20 #7 Senior Member     Uwe Pilz Join Date: Feb 2017 Location: Leipzig, Germany Posts: 742 Rep Power: 14 > I am currently having an issue on which source term should be excluded to be able to make it axisymmetric. Does anyone understand my question here? I only have experiences with changing a 2D geometry in a cylindric one with the help of MakeAxialMesh. The tool needs to be added to a standard installation: http://openfoamwiki.net/index.php/Contrib_MakeAxialMesh The tool warps a 2d geometry in an axialsymetric one. The result is still 3d, that means 1 cell thick in radial direction (was the z direction). The wedge boundary condition has to be used at these boundaries. As far as I understand this b.c. takes into account that the planes are not parallel anymore. So "empty" cannot be used. You don't need to use that tool. It is not too hard to create a axial symmetric geometry form scratch. Start with a wegde and add hex elements which get larger in r direction. The wedge b.c. has to be used too. In short: The geometry remains 3d as always in openfoam. __________________ Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)

 April 2, 2017, 18:15 #8 Member   OpenFoam Join Date: Jun 2016 Posts: 82 Rep Power: 8 Dear Pilz, Thanks again for your time and clarifications. My issue is not that I was not able to create an axiysmmetric mesh from a 2D geometry but instead the main issue is that the three body forces introduced have to be adjusted in the code in order to perform axisymmetric simulations. I need to reduce the problem into two dimensions through the three body forces introduced earlier i.e. fx, fy, fz. I will provide more detail tomorrow so that you can understand what am trying to do. Thanks again,...

 April 19, 2017, 18:44 #9 Senior Member     CFD Join Date: Nov 2010 Location: United States Posts: 243 Rep Power: 15 Hi, I think that you need to assume the forces are uniformly distributed along the circumferential direction. Hope that helps,