Dimensionless wall distance and velocity in paraview

Sören Sander · November 24, 2015, 11:00

Hello,

I have a 3D mesh (channel) and want to calculate the dimensionless velocity profile to compare it to the theory (wall law). Right now I create a "plot over line" and save the data to a file. Then I postprocess this data to get the dimensionless profile.

As "plot over line" creates new points and interpolates OpenFOAM data at these points, one cannot see the position of each cell in the layer. I want to check, how many cell I got in each layer and where they are, but I do not know how to extract cell values along a line including coordinates.

Is there any way to do this in paraview? Or is there another tool, e.g. provided by OpenFOAM to do the task? Can I create y+ and u+ profiles directly in paraview? I guess tau_wall is unknown and need to be provided; afterwards I would use the calculator?

Best regards,
Sören

Bazinga · November 26, 2015, 03:35

You can use the yPlusRAS utility to get the values of the non dimensional wall distance for an RANS simulations:

http://cfd.direct/openfoam/user-guid...ard-utilities/

To examine the values over a line you can use the sample utility.

http://cfd.direct/openfoam/user-guide/sample/

Sören Sander · November 26, 2015, 04:13

Hello Bazinga,

thank you very much for your answer. Unfortunally, yPlusRAS only "Calculates and reports yPlus for all wall patches, [...]", but I need the values for internal mesh points as well. To my knowledge, the "Plot over line"-tool in paraview only interpolates values, but does not provide any information on the original cell-values as calculated by OpenFOAM. So it is not possible to extract the OpenFOAM-values this way.

Bazinga · November 26, 2015, 04:54

For the second part. To get the cell values without interpolation instead of using paraview you can use the sample utility. This will give you what you need. But i do not know how to get the y+ values in the flow field.

Bazinga · November 27, 2015, 02:50

If you get the value of y+ at the wall you can calculate u* using the viscosity of the fluid. Then, if you know the wall distance of each cell you can calculate the y+ value for each cell. To get the cell position I think you can use the writeCellCentres utility.

November 24, 2015, 11:00	Dimensionless wall distance and velocity in paraview	#1
Sören Sander Member Sören Sander Join Date: Sep 2012 Location: Germany Posts: 43 Rep Power: 14	Hello, I have a 3D mesh (channel) and want to calculate the dimensionless velocity profile to compare it to the theory (wall law). Right now I create a "plot over line" and save the data to a file. Then I postprocess this data to get the dimensionless profile. As "plot over line" creates new points and interpolates OpenFOAM data at these points, one cannot see the position of each cell in the layer. I want to check, how many cell I got in each layer and where they are, but I do not know how to extract cell values along a line including coordinates. Is there any way to do this in paraview? Or is there another tool, e.g. provided by OpenFOAM to do the task? Can I create y+ and u+ profiles directly in paraview? I guess tau_wall is unknown and need to be provided; afterwards I would use the calculator? Best regards, Sören Gang Wang likes this.

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November 26, 2015, 03:35		#2
Bazinga Senior Member Join Date: Jun 2012 Location: Germany, Bochum Posts: 230 Rep Power: 16	You can use the yPlusRAS utility to get the values of the non dimensional wall distance for an RANS simulations: http://cfd.direct/openfoam/user-guid...ard-utilities/ To examine the values over a line you can use the sample utility. http://cfd.direct/openfoam/user-guide/sample/

November 26, 2015, 04:13		#3
Sören Sander Member Sören Sander Join Date: Sep 2012 Location: Germany Posts: 43 Rep Power: 14	Hello Bazinga, thank you very much for your answer. Unfortunally, yPlusRAS only "Calculates and reports yPlus for all wall patches, [...]", but I need the values for internal mesh points as well. To my knowledge, the "Plot over line"-tool in paraview only interpolates values, but does not provide any information on the original cell-values as calculated by OpenFOAM. So it is not possible to extract the OpenFOAM-values this way.

November 26, 2015, 04:54		#4
Bazinga Senior Member Join Date: Jun 2012 Location: Germany, Bochum Posts: 230 Rep Power: 16	For the second part. To get the cell values without interpolation instead of using paraview you can use the sample utility. This will give you what you need. But i do not know how to get the y+ values in the flow field.

November 27, 2015, 02:50		#5
Bazinga Senior Member Join Date: Jun 2012 Location: Germany, Bochum Posts: 230 Rep Power: 16	If you get the value of y+ at the wall you can calculate u* using the viscosity of the fluid. Then, if you know the wall distance of each cell you can calculate the y+ value for each cell. To get the cell position I think you can use the writeCellCentres utility.