Khamsin Virtual Racecar Challenge 2014

[astracrazy]

Just a curiosity (I'm going to use Khasmin only after the first race, I'm too late at the moment): the first number (34.7833) is the lateral resultant (near to zero)? And the numbers in the second group are the postition of the resultant forces (so 2.13449 should be the COP)? Is that a Monaco 2013 setup?

I don't know, i guess it must be? Handy if it is as it will save me finding it in paraview which is a pain. It wasn't related to any track it was just a run i did last year.

Regarding intake rule:
There will be no rule change regarding this (this year anyway). Its something which has been in it from the start so we are talking at least 2 months. It doesn't really matter if i agree or disagree but we have to keep it fair.

I'm up for clearing up any potential grey areas, if they occur, but making actual rule changes only hands an advantage to some and greatly disadvantages most others who have kept to the rule.

Bare in mind with the intake rules there needs to be some element of "keeping them exposed" to create the drag penalty (which is realistic)

[CAEdevice]

OK, I think that the decision to not change any rule during the contest is right. It's too late to change it: with my question I only wanted to explain a doubt.

[astracrazy]

ye no problem

[RicME85]

Ive never really understood the numbers produced by Khamsin, will no doubt be clearer come Saturday when Julien does the Hangout

[variante]

providing before you ran the sim you Right-click->Define->Monitor Forces then in khamsin right click -> analysis -> output. it opens a text file. scroll down and find something like

forces(pressure, viscous)((34.7833 1386.02 -3085.12) (-0.0607569 2.13449 0.410286))

in bold = drag and downforce

Just a curiosity (I'm going to use Khasmin only after the first race, I'm too late at the moment): the first number (34.7833) is the lateral resultant (near to zero)? And the numbers in the second group are the postition of the resultant forces (so 2.13449 should be the COP)? Is that a Monaco 2013 setup?

(-0.0607569 2.13449 0.410286) These are the numbers concerning viscous friction (-->skin friction); they're still in Newtons. That series doesn't rely on pressure differentials, as the first series, but on the friction between the medium and the bodywork.

Basically, since the medium is "air", which interferes minimally, you can simply ignore the second series and concentrate your work on the data given by the first one.

To calculate COP (centre of pressure): divide the greatest(hopefully) number you find in the "moment" section by your downforce.
( COP = torque(on the right axis) / downforce )

[julien.decharentenay]

Thanks Variante for stepping in.

The total drag is: 1386.02 + 2.13449 and total downforce is: -3085.12 + 0.410286. The set of numbers are pressure induced forces and viscosity induced forces.

The COP can be approximated as mentioned by Variante - but this would be an approximation as it would only account for the component of drag in the y-moment. On request from Luke (and I think I did this last year as well), you will find a spreadsheet at http://www.khamsinvirtualracecarchallen ... ects=0&d=1 where you can copy forces and moment and it will return the drag, downforce, COP as well as Cd.A and Cl.A.

Note: for the challenge the drag, downforce and COP are averaged over the last 50 or so iterations to obtain an average value. Please also note that we are checking convergence of COP - make sure your simulation is well converged.

[julien.decharentenay]

Using last years 100mph no yaw tunnel I got this:

Mesh stats
points: 549768
faces: 1350654
internal faces: 1209661
cells: 404277
boundary patches: 13
point zones: 0
face zones: 0
cell zones: 0

Looking in the scenario_0 folder (the one from the portal) I dont seem to have analysisOutput

The cell count looks very low. With last year setup I would be expecting around 1 Millions cells. This year, the cell count is likely to be around 2.4 to 2.8 Millions cells.

The portal does not generate analysisOutput, as it is just a redirection of the screen output. To get the cells count, open an openFoam terminal, go to the case directory and type "checkMesh".

[astracrazy]

Thanks for uploading that Julien i think it will help everyone

[RicME85]

I HATE Linux!

I have finally got OpenFOAM installed on a Linux laptop, now Im having issues trying to install Swak4FOAM

[astracrazy]

+ 1 for both. I gave up in the end

[julien.decharentenay]

I would be happy to help with Linux and swak4Foam installation. Let me know and we can organise a screensharing exercise so that I can have a look at the errors.

Hangout on Air is on at: https://plus.google.com/u/2/events/c789 ... g650p48s6s

[julien.decharentenay]

Due to technical issues. Video call is at: https://plus.google.com/u/2/11064138755 ... sts?cfem=1 and passive viewer at http://youtu.be/bIScY23DLXI

[RicME85]

Thanks again to Julien, a fountain of knowledge with a cool accent

I highly recommend Dan gives the video a look once it has been edited if he didnt get to watch any of the hangout.

I would definitely like to pick your brains on this Linux and Swak4foam business whenever you are free. I know you said the best guys to help are already doing so on the cfd forum, problem is my knowledge of Linux is so basic that I get very lost when they suggest things
Would love to be able to compile OpenFOAM and Swak4foam for Windows so that it can be shared for all to use, do you know how to compile?

[cdsavage]

Is anyone else getting "Error when retrieving case information details from server" when trying to use the portal? I can see it uploading if I watch network activity on my PC, but then I get that error.

[RicME85]

Just tested it for you and get the same result