boxTurb strange error

sudheer717 · November 10, 2016, 15:26

Hello Foamers,

I am trying to use boxTurb utility to create turbulence field in my domain. I have generated an uniform mesh with 101 nodes in each direction. So my total number of cells as reported by checkMesh are 1000000 which is what I wanted.

This is the output from checkMesh:

Code:

Mesh stats
    points:           1030301
    faces:            3030000
    internal faces:   2970000
    cells:            1000000
    faces per cell:   6
    boundary patches: 7
    point zones:      0
    face zones:       1
    cell zones:       1

Overall number of cells of each type:
    hexahedra:     1000000
    prisms:        0
    wedges:        0
    pyramids:      0
    tet wedges:    0
    tetrahedra:    0
    polyhedra:     0

When I run boxTurb, it throws me the following error.

Code:

Create mesh for time = 0

Reading field U

Reading boxTurbDict

--> FOAM FATAL ERROR: 
number of elements in direction 0 is not a power of 2
    Number of elements in each direction = 3{100}

    From function fft::transform(complexField&, const labelList&, transformDirection)
    in file fft/fft.C at line 58.

FOAM aborting

I have read other posts about this utility, there the error was reported as the user had some grading in the mesh. So, I made the mesh uniform.

Any ideas on what I am missing or doing wrong ?

Thank you
Sudheer

sudheer717 · November 13, 2016, 15:52

My bad, I misread the information given in the error message. I thought the number of elements should be of form N^2 while it expects them to be of form 2^n.

Now it is clear and resolved.

Uyan · June 30, 2017, 16:33

sudheer,

Do you know what are Ek and k0 , in boxturb utility really means.

I need to make a decaying turbulence in a box with certain integral length scales, how do i relate my known length scales to Ek and k0?

Thanks.

sudheer717 · June 30, 2017, 17:16

Hi Uyan,

The constants in the boxturb are Ea and k0. They are used inside Ek.H to evaluate the Turbulence Energy spectra with respect to the wavenumber k.

Ek.H is in OpenFOAM-x.x.x/src/randomProcesses/turbulence/Ek.H

I would recommend you to look at this paper:

Martinez, D.O., Chen, S., Doolen, G.D., Kraichnan, R.H., Wang, L.P. and Zhou, Y., 1997. Energy spectrum in the dissipation range of fluid turbulence. Journal of plasma physics, 57(1), pp.195-201.

November 10, 2016, 15:26	boxTurb strange error	#1
sudheer717 New Member Sudheer Reddy B Join Date: Oct 2015 Location: San Antonio, Texas Posts: 9 Rep Power: 11	Hello Foamers, I am trying to use boxTurb utility to create turbulence field in my domain. I have generated an uniform mesh with 101 nodes in each direction. So my total number of cells as reported by checkMesh are 1000000 which is what I wanted. This is the output from checkMesh: Code: Mesh stats points: 1030301 faces: 3030000 internal faces: 2970000 cells: 1000000 faces per cell: 6 boundary patches: 7 point zones: 0 face zones: 1 cell zones: 1 Overall number of cells of each type: hexahedra: 1000000 prisms: 0 wedges: 0 pyramids: 0 tet wedges: 0 tetrahedra: 0 polyhedra: 0 When I run boxTurb, it throws me the following error. Code: Create mesh for time = 0 Reading field U Reading boxTurbDict --> FOAM FATAL ERROR: number of elements in direction 0 is not a power of 2 Number of elements in each direction = 3{100} From function fft::transform(complexField&, const labelList&, transformDirection) in file fft/fft.C at line 58. FOAM aborting I have read other posts about this utility, there the error was reported as the user had some grading in the mesh. So, I made the mesh uniform. Any ideas on what I am missing or doing wrong ? Thank you Sudheer

June 30, 2017, 16:33	boxturb	#3
Uyan Member Join Date: Feb 2014 Posts: 63 Rep Power: 13	sudheer, Do you know what are Ek and k0 , in boxturb utility really means. I need to make a decaying turbulence in a box with certain integral length scales, how do i relate my known length scales to Ek and k0? Thanks.

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November 13, 2016, 15:52		#2
sudheer717 New Member Sudheer Reddy B Join Date: Oct 2015 Location: San Antonio, Texas Posts: 9 Rep Power: 11	My bad, I misread the information given in the error message. I thought the number of elements should be of form N^2 while it expects them to be of form 2^n. Now it is clear and resolved.

June 30, 2017, 17:16		#4
sudheer717 New Member Sudheer Reddy B Join Date: Oct 2015 Location: San Antonio, Texas Posts: 9 Rep Power: 11	Hi Uyan, The constants in the boxturb are Ea and k0. They are used inside Ek.H to evaluate the Turbulence Energy spectra with respect to the wavenumber k. Ek.H is in OpenFOAM-x.x.x/src/randomProcesses/turbulence/Ek.H I would recommend you to look at this paper: Martinez, D.O., Chen, S., Doolen, G.D., Kraichnan, R.H., Wang, L.P. and Zhou, Y., 1997. Energy spectrum in the dissipation range of fluid turbulence. Journal of plasma physics, 57(1), pp.195-201.