[Massimodecimo]

Hi everyone,

I've done some simulations with a 3D wing and I'm looking for a way for computing the forces in each point of the surface mesh. In the surface_flow there are Cp and Cf values but for obtaining the forces I need the normal vectors. How can I retrieve the Normals directly from SU2?

[bigfootedrockmidget]

The normal forces are not being written to any file. But you can construct the normal forces in paraview if you save the results in paraview .vtm format (then it is easy to extract the surfaces that you need for the force calculation)

[Massimodecimo]

Hi, do you intend to use a programmable filter in Paraview? Is there a convenient way? Because I obtained the normals faces in the triangles of the mesh but I'm not sure how extracting the normals in the grid point where SU2 compute the Cp and Cf.

[bigfootedrockmidget]

Have a look at this statefile:
https://github.com/bigfooted/su2case...eseries_3.pvsm


It was used to make the first movie, force distribution on a vortex shedding cylinder, that is shown here:
https://github.com/bigfooted/su2cases/tree/master


The input should be a vtm file, there is one here:
https://github.com/bigfooted/su2case...inder_farfield


In the statefile, the force normal to the surface is computed using pressure * normal
The lift is then computed again by taking the normal in the vertical direction.


The programmable filter is simply this:

from vtk.numpy_interface import algorithms as algs
 import numpy as np
 

 input0 = inputs[0]
 numCells = input0.GetNumberOfCells()
 

 normx = np.empty(numCells, dtype=np.float64)
 normy = np.empty(numCells, dtype=np.float64)
 normz = np.zeros(numCells, dtype=np.float64)
 for i in range(numCells):
   cell = input0.GetCell(i)
   p1 = input0.GetPoint(cell.GetPointId(0))
   p2 = input0.GetPoint(cell.GetPointId(1))
   nx = p2[1] - p1[1]
   ny = -(p2[0] - p1[0])
   normx[i] = -nx/sqrt(nx*nx+ny*ny) 
   normy[i] = -ny/(sqrt(nx*nx+ny*ny))
 

 norm = algs.make_vector(normx, normy, normz)
 output.CellData.append(norm, "normals")
p, li { white-space: pre-wrap; }

[Massimodecimo]

Thanks for helping me.

Is the programmable filter for a 3D case? I don't understand how could be the norm in the z direction always 0

[bigfootedrockmidget]

The cylinder case is 2D, you can just add the z-coordinate in a straightforward way...