[KVRC ~ish] CCE LMP01

[CAEdevice]

Thank you Machin!
I insist (it will be one of my proposal for the KVRC2016): this thread should be collected in a booklet provided to all the team who will participate.

[machin]

Thanks Matteo, you are too kind!

[RicME85]

The last two pages have cleared a lot of things up for me, the start of the thread was a lot of technical number crunching that went well over my head but now I think I can make some real improvements if I get the time to sit down and assess things properly.

Will definitely try and get both versions of my car you have designed drawn up now that I am back home, will be interesting to see the difference in numbers between the original car and the ideas you had Richard.

[LVDH]

I always thought the purpose of the open sides was to encourage air through the front end aerodynamics... rather than any attempt at supplying the diffuser, but to be honest one thing I've learnt about aerodynamics is that it is bloody complex!

My thinking was this: air will always take the easiest route around an object (or in scientific-speak: "It follows the pressure gradient"): to ensure that the air goes through the front-end aero (rather than around the sides of the car), you want an unrestricted flow between the wheels and out towards the back of the car, opening up the sides like this (in my thinking) increases the ease with which air can flow through the front end... Essentialy, it has more ways to "get out" once it has been between the front wheels: either over the sidepod, or down the sides....

However, I am intrigued by your finding that it "doesn't work". In terms of aero coefficients, how does it affect the results? Reduction in Cl.A? Increase in Cd.A and/or drastic change in COP (if so, which way; forwards or backwards)?

OK, I took the time to start looking into this.
Here are two pictures with stream lines entering the gap in my front wing and also on the sides:

Closed side pod:


Open side pod:


I could not produce any streams leaving the large side gap. More detailed post processing confirmed that (on my car) no significant amount of air leaves this large gap.

If you look at the floor you can see that on both configurations the air entering the diffuser section does its magic in a similar fashion creating some down force:

Closed side pod:


Open side pod:


I also created some surface stream lines:

You can see that the air flow behind the front wheel is nicer on the open version of the side pods.

Sorry that you cannot see everything but I have to keep some secrets until the end of the season.

So time to look at the numbers:
The open version has 1.7% more drag and 1.4% more down force. The CoP is shifted forward 5cm. So maybe the front wing airflow is indeed slightly improved.

Somehow I still do not quite see why to put these open side pods onto my car. But these cars are very delicate when it comes to getting all parts working together. So on others they might be the way to go.

[machin]

The last two pages have cleared a lot of things up for me, the start of the thread was a lot of technical number crunching that went well over my head but now I think I can make some real improvements if I get the time to sit down and assess things properly.

Cool. I must admit: I like the numbers... but I think you are right: general rules and interpretation of the CFD results is far more useful to the improvement of the car... If we do compile some of this info into a booklet for next year I'll take that into account.

[machin]

OK, I took the time to start looking into this.
Here are two pictures with stream lines entering the gap in my front wing and also on the sides:

...

So time to look at the numbers:
The open version has 1.7% more drag and 1.4% more down force. The CoP is shifted forward 5cm. So maybe the front wing airflow is indeed slightly improved.

Awesome! The interesting thing for me is that the change (which looks like quite a big difference) doesn't really make a huge difference in reality... I'm guessing that with some refinement both solutions could be made to work equally as well as each other...

[CAEdevice]

My simulations confirm LVDH (Mantium) conclusions. The presence of open sidepods on my car is more related to the upper flow of the car and it does not feed the diffuser.

[RicME85]

Would that be because of the requirement for the front suspension to not be visible and thus sending more air up and over rather than through the front of the car and out the side?

[machin]

The open version has 1.7% more drag and 1.4% more down force. The CoP is shifted forward 5cm. So maybe the front wing airflow is indeed slightly improved.

Some quick mental arithmetic on those numbers (using your Round 4 results as a baseline: Cd.A of 1.03, Cl.A of 5.02 and COP of 1.567m) suggests that opening up the side pods has increased the front downforce by 5% and decreased the rear by about 2%, with an efficiency (Lift:Drag) of about 4:1...

...for a high downforce track (and coupled with a rear wing adjustment to get the COP back where we want it) that's actually not a bad little change...

Given those numbers alone I would have guessed that it had to do with improving front end flow, to the detriment of flow to the rear wing... Except as you say, the streamlines do not support that theory... But clearly something is better at the front and something slightly worse at the rear...

[variante]

Ducting air more effectively through that vent might be of great help (i.e. gaining back the right pressure/velocity). As Mantium said, these cars are delicate, and, in order to verify the effectiveness of a certain device, a well thought design is necessary.

So we should ask ourselves: what kind of airflow do we need in that area? and why? Is our aim to reduce drag or to increase downforce? if the latter, front of rear downforce? in which way, in particular? (and so on...)

I'm quite sure that a generically designed device will lead to a generic, probably unsatisfactory, result. Instead, if we start designing something to achieve a precise target, the result will be clearer and the device itself will be proven fully effective.

This being said, i've never done a direct comparison for those exact layouts. I have done, however, such comparison for the fully open sidepods, the ones CAEdevice and I are using: the results are clear and impressive.

[machin]

I'm quite sure that a generically designed device will lead to a generic, probably unsatisfactory, result. Instead, if we start designing something to achieve a precise target, the result will be clearer and the device itself will be proven fully effective.

It was a useful exercise in its current form though, as it just goes to show that once you've got to a certain level of performance, there are no "easy wins", even if you make what looks to be a reasonably large charge....

[LVDH]

I created one more detailed view:


The design I created was more intended to direct air to the diffuser.
Variante's and CAEdevice's cars seem to want to direct air towards the rear upper deck of the car.
I do not think this would work on my current design. The beam wing would probably be happy about it though.

[variante]

From the last image it's clear that the flow around the front wheel cover stalls pretty badly. This fact invalidates the results of the annexed test.

In order to avoid the stall i would bring wheel cover and pods closer to each other, or design a more gentle wheel cover, or introduce a flow conditioner in the middle.

Also, it doesn't seem to me that LVDH's pods layout suits that opening at all. What suits perfectly that opening is an LMPrototype layout (similar to Talno's, Kineuton's and Sjns' cars, to give an idea).

Finally, i insist that when designing a new part it's necessary to have in mind what is the exact target.
Why would that flow feed more air to the diffuser, for example? If that airflow happens to have inferior pressure compared to the stream otherwise present in that area, it would feed LESS air to the diffuser (which is not necessarily a negative thing, as it would increase the sealing effect of the floor)

[MadMatt]

Interesting pictures LVDH, thanks for sharing! There is indeed a large recirculation region here! variante's advice might solve this, but what we also see is that air flow coming from the side of the car effectively blocks the airflow coming from the front wing area that might escape through the opening.

[RicME85]

Hi Ric,

I took the liberty of looking through your previous designs and your results and I see that you already had a lot of those features on your previous cars....

I think your round 3 car looked pretty good... I'm wondering if it might make a better starting point, if for no other reason than you already have a set of aero coefficients with which to work with...

http://i.imgur.com/bPGI0my.jpg

First thing would be to tidy up the side pod/crash structure....

The next step would be to graft on the diffuser exit from your round 4 car:

http://i.imgur.com/nNQGlTL.jpg

Both those should tidy up the car, and reduce drag a little, but don't expect miracles.

The round 3 car had quite a front bias to its downforce, which essentially means the front end is producing a lot more drag for additional downforce that the car can't utilise. I would be inclined to lose one element from your upper front wing: this should improve your balance and overall efficiency.

Again, we can't expect miracles with these changes, but I think that leaves you with a good basis to start with. I took the liberty of photoshopping what the car might look like (a picture paints a thousand words and all that).

http://i90.photobucket.com/albums/k248/ ... uydt0f.jpg

There's an interesting article in the latest Racecar Engineering in which they made an F1 car model and subjected some changes on it to see what effect they had: trimming a small amount OFF the diffuser width manipulated a vortex sufficiently to increase downforce by 10% AND reduce drag: i think the moral here is that once you've got the basics sorted there are going to be no easy wins: to match the front runners requires some pretty in-depth CFD analysis.

Perhaps you could post some CFD images from under the Diffuser of your Round 4 car and we can try and figure out what's going on. Start with a surface pressure plot...?

I have made the changes you suggested to the diffuser. I have move the crash structure forward to roughly the same position as you suggested along with shrouding it in a teardrop. I have also changed the front suspension cover to a teardrop shape as the one on the car originally was like a curved L shape rotated to cover the suspension.