Khamsin Virtual Racecar challenge 2013 (CFD model racing)

[astracrazy]

i've been thinking about the 2014 sidepod rules and making them simple but regulated - to avoid unrealistic sidepods

what about making it simple. one of two choice boxes must fit within the sidepods

1 is quiet short but wide the other in quiet thin but long? You then have the option to make either wide sidepods but shorter or thinner side pods but longer? how you design your sidepod around the boxes is up to you?

and the leading edge of the sidepod can have a radius of no greater than 80 degrees (to avoid people making sidepods square up to the box)

just putting it out there....

[variante]

I'd agree with that, but those boxes should be well designed, otherwise they would limit our design possibilities.
The alternative is to adopt a cross section with a minimum area to be placed at a given distance from, lets say, rear wheel center line.

and the leading edge of the sidepod can have a radius of no greater than 80 degrees (to avoid people making sidepods square up to the box)

It would be enough to follow F1 technical regulations, which require 75mm radius for the sidepods.

And about regulations to adopt for the next season, i propose to keep on using official F1 regs, the comprehension of which should be helped by an improved regulation tub to be given to participants.

[RicME85]

Personally I dont see the need to simplify things.
Follow the official FIA F1 regulations, supply a better tub/wheels/suspension model and also include a catalogue of default parts that have to be fitted in.
Powerplants are going to be all sorts of crazy shapes and sizes, there is scope for different gearboxes and radiators too.
Or if not a variety of parts, why not a default set of volumes that need to fit within the body work.

[CottrellGP]

Hi all,
Just a little confused, when looking at the results etc, which figures are the drag figures?

[machin]

in the results table the drag is expressed as "Cd.A" which is the Coefficient of Drag multiplied by the car's projected frontal area (in metres squared).

[cdsavage]

To give you an idea of what I would want to use for the mesh size:



Mesh used for round 1/2:



The denser mesh was useable for a whole-car sim, but I had the advantage of being able to use different mesh sizes for different parts of the car. I think ideally the mesh size should be somewhere between the two, and at the very least be dense enough to resolve slot gaps etc. I think the boundary layer mesh is also something to consider, even if its only a few layers. Either way, I still think its a no-brainer in terms of accuracy to increase the density of the mesh in exchange for only running 1 simulation per car.

[AratzH]

I have to agree that mesh size is critical and some designs might be suffering because of that. I got DNF'd in both races so I wouldn't change much for me, but to show what I mean I did a couple of tests with two mesh sizing schemes. The first one with the same mesh used for Monza and the other with a mesh optimized to fully simulate the slots in the multiplane wings.



As it can be seen the Cd doesn't change much but the Cl suffers a major 26% decrease because of the lack of precision in the slot simulation. Bea in mind that in order to speed up the simulations the rotating tires were not simulated, but the relative difference should still hold truth.

Now I repeated the same simulation as in the 7.8mm cell size but with narrow channel refinement. This is a technique were the meshing increasees its resolution locally where a narrow channel is found, such as the slots between wing elements. It is a common consideration that for accurate results, there should be at least 6 elements/cells between two close walls. This technique allows this without extremly increasing the total amount of cells.



The results show that, while the Cd did not change much, the Cl increased a 20% compared to the unrefined version. Computation time on the other hand was almost 3 times more. I think it would be good to make a test with the same software and compare the results you get between different mesh schemes.

Now to finish and just to show the big dependency of the results of CFD simulation with mesh size and type take a look at this video:
http://convergecfd.com/movies_new/sandia-flowbench.avi

Regards

[etsmc]

Just a questing on the virtual stopwatch. how long does it take to get the result after inputting the data??

just thinking out loud here but if it takes in to account the engine power curve, so would it be possible to give teams the option of an engine to use say a selection of 3 all having a different power and curve??
If the tests take too long then its not with doing but the questions floating about with standard parts then 3 different engine models could be made of different sizes making the teams have to fit the engine in their body work depending on which engine they choose...

i know this is a CFD competition so the test could still be run for everyone with the default engine curve for comparison.

[machin]

Once you type in the Aero coefficients the lap time generation is pretty much instant... each engine has its own power curve, mass and rotating inertia. So it would technically be possible to have different engines in the competition.... however personally I don't think it adds anything in this case since; all real f1 engines are very close in terms of power output and size anyway. Other things that could be added is gear ratio selection, different wheelbases, different CG height, etc etc however, as we have seen; its already proving quite a challenge just having the aero side of things being adjustable... let alone adding everything else.... better to concentrate on the aero side in my opinion.

[Paul]

Is there an option to optimize the gear ratios for a given aero pack? That would make different directions as regards drag/down-force more feasible, as, for example, a long 7th gear would hinder a high drag solution and vice versa...

[astracrazy]

question for anyone doing there own testing on there cars. are you using drag and downforce forces i.e measuring in Newtons. or are you using coefficients cl and cd

i'm using forces, but it doesn't seem to have much relevance so i think i'm gonna switch to coefficients.

[cdsavage]

Any update on what mesh size will be used for the next round?

[machin]

Is there an option to optimize the gear ratios for a given aero pack? That would make different directions as regards drag/down-force more feasible, as, for example, a long 7th gear would hinder a high drag solution and vice versa...

Ratios are adjustable in Virtual Stopwatch of course, but again, I think it is an over complication for this challenge to allow teams to adjust them... At the moment the ratios are set so that they give a fairly high theoretical top speed; not optimum for low speed tracks, but it is the same for everyone. This is similar to the real F1 rules for 2014 where the 8 (as opposed to 7) gear ratios will be fixed throughout the season (unless I'm mistaken). I think making adjustable gear ratios is an over complication for this challenge; getting the aerodynamics sorted is a challenge enough in itself!

EDIT; I should just say however; this is Nick/Julian's championship; I just provide the lap time calculation software, so if they want to allow you guys to choose different engines/adjustable gear ratios, etc etc then it is up to them; the software is more than capable of doing it.

[N12ck]

Hi All,

I think we would have to assess, is this a team setup challenge? is this an aerodynamic challenge? at the current moment it is an aerodynamic challenge, however we would have to assess the pro's and con's of looking at expanding into engine choice and gear ratio choices.

The risk with moving away from being a pure aerodynamic challenge is it risks becoming too complex when trying to develop a car. For example, when a person is in a race team, he does 1 job in 1 department. To make it more than an aerodynamic challenge risks isolating those who do not have great knowledge of gearing ratios and other factors. Where as if your car is slow at the moment, we know it is the aerodynamics that is the issue and the person could sort the issue quickly and diagnose it, if more factors were brought in, how would you know what was wrong?

What is everyone's views?

Many Thanks
Nick

[astracrazy]

i say keep it aero only. aero can already by complicated