[KVRC] Khamsin Virtual Racecar Challenge 2016

[Alonso Fan]

ok, so I have one more question. how do I conduct a full analysis on the car? at the moment I am just using the kvrc option on body.stl
how do I get occfd to calculate pressure at inlet and outlet etc. what I mean to say is, how do I use the other stl files, like cooling-intake.stl and area-template.stl?

[CAEdevice]

You have to cut their surface and to save them as separated stl.

[Alonso Fan]

You have to cut their surface and to save them as separated stl.

they are already saved as separate .stl files, but how do I get occfd to use them?

[RicME85]

Create a folder, put the stl files in the folder then go back, right click on the folder.
I always have folders named like Race 1 Car - Test 1 which will have all the SKP files. Within that folder I will create a folder called OCCFD and put all the correctly named STL files in it.
Once that is done I go back to the Race 1 Car - Test 1 folder and right click on the OCCFD folder and select whichever option I want to use.

[Alonso Fan]

thanks, that's what I was after

thanks so much!

[Alonso Fan]

I've done 3 simulations today and all have post processing issues...

but the final simulation is the most weird...



what am I doing wrong?

[RicME85]

Its an issue with the mesh. Had similar and iirc Chris said it was meshing the inside and outside of the model thus giving the weird mapping in Paraview.
Need to make sure the model is watertight

[CAEdevice]

It seems that you had the "internal mesh issue". It happens when a gap makes the mesher not able to distinguish between internal and external side.

Would you have the possibility to export a step? I will be happy to take a look and run a simulation.

Edit: I did not see Rich's post. As he wrote the body is not watertight.

[CAEdevice]

Btw: interesting geometry!

[Alonso Fan]

thanks, is the issue caused by me not making the .stl files correctly?

I sincerely appreciate your offer CAEdevice, but I don't want to waste your time. and i'm not sure if i can export in step, but i can try...

[Alonso Fan]

Btw: interesting geometry!

it's not fast, i promise...

[Alonso Fan]

I've just read through the forces in the log and I was somewhat disappointed that my car was producing upforce...

[sjns]

I've just read through the forces in the log and I was somewhat disappointed that my car was producing upforce...

Beware that the meshing issue can have a huge effect on the calculated coefficients. Most of the time it will give unrealistisc results. Chances are good your car isnt producing lift.

[LVDH]

The guys are right. You have to find the crack in your model. It might be very small or maybe even so big and obvious that you will overlook it a few times.

Here is how Paraview can help:

• Load the stl file of your car body

• Make sure it has a boring color like gray

• With the stl selected in the tree on the left go to Filters>Feature Edges

• You will have to play with the feature angle, 150 is a good start

• Scroll down a bit in the menu of the feature angle until you find line width and change it to three

• Change the color of these new lines to something striking like a neon red

What you should now see are feature edges of your car. You will have to play with the angle a bit (do not forget to press apply). Some feature angles are supposed to be there like the hard edges of the wheel houses. With a bigger angle they might disappear. But with some luck you will notice edges that should not be there when approaching 180 degrees. You can check by changing the representation of the stl from "surface" to "surface with edges". If you see strange triangles not matching the neighbors you have located your problem.

If you get it solved, the car will not only produce much better numbers but the simulation will also be faster.

[CAEdevice]

The limit I have is that I am not able to extract the pressure differential and to write it in a log (as it happens with the areo forces).

Sorry about not having taken up on your earlier query on this. To extract the pressure differential, please do the following:

- Start ParaView;
- Open the openFoam file;
- Only select the boundary condition (in the part option) that you want to calculate the surface integral of pressure on;
- Apply a calculator filter;
- Set a new field "Pressure = 1.2 * p" (the pressure calculated and output by openFoam is normalised by the density);
- Apply the Surface Integral Filter;
- the surface integral of pressure is reported under Pressure.

Change the selected boundary condition to extract the value at the other surface.

Another issues for a beginner is the manage the double start (preliminary run). What about starting directly from the second stage?

You can, but it just takes longer to establish, hence more iterations...

I finally managed to find a way to calculate the integral of presisone with Paraview (thanks Julien ), however , there is something wrong with the post processing (it fails very often when generating the pictures): it would be useful to calculate the COP by hand (I do it approximating the drag resulting position) . What is the algorithm used by OCCFD ? Would it be possible to include the COP in a text report ad not only in the HTML report ?