SimScale CAE Forum

How to determine the coefficient drag


#1

i have determined a drag force of 220 Newtons at a speed of 25m/s, 1.225kg/m^3 and an approx area of 1.84m^2, i got a mathematical value of 0.3125 but the area is very approximate, is there a way of determining it in processing?


Drag Coefficient result?
#2

Hi @Lemlurker,

You have to manually specify the frontal area. You can do this in Paraview. So far, the best tutorial on how to do it in Paraview comes from http://www.vespalabs.org/projects/vespa-cfd-3d-model/openfoam-vespa-tutorial

But I had to modify some steps in order for this to work. I’ll step you through (This works for Paraview 5.x):

  1. Load the STL file and tick off Camera Parallel Projection.
  2. Select Points On in the front view of the car.
  3. Extract Selection based on the points you selected.
  4. Transform the extracted points in order to project them on a flat surface. For the next step to work properly, we have also to rotate them so they lie on the XY plane.
  5. Apply the Delaunay 2D filter.
  6. Integrate Variables to get the result.

The area measured by this method is of 2.37032 m2, which is very close to the 2.367 m2 I measured using proprietary software.

In step 2, if using Select Cells On, the resulting area is of about 1.9x m2 as it misses many cells with this particular geometry:

Hint: the filters Extract Selection, Transform, Delaunay 2D, and Integrate Variable are located under Filters. But you may add the quickly to the pipeline with Ctrl + Space and typing their name in the search box.


'Drop Capsule 1' simulation project by C0YL3
#3

thanks for the info, though having a few issues doing it myself, the extract selection button is greyed out and does nothing, any ideas?


#4

Make sure you hit the Apply button whenever you add a filter. Also, you should see the vertices coloured pink in order to extract them.


#5

ah thats it, the apply button thanks