[KVRC ~ish] CCE LMP01

[machin]

I've been using these [front] suspension covers for the first half of the champioship. Notice the angle given to the airflow leaving the covers: it's pretty much zero, so it doesn't mess up the downstream airflow.

The suspension fairing itself is now producing less lift, but it does look like it is pulling air out of the floor inlet area (see balloon 1), which does mean that the diffuser area (balloons 4 & 5) are producing less downforce now. However, modifying the underside of the suspension fairing will likely lead to a re-loss of some of the front end downforce, which isn't exactly highly abundant as it is: that's why I think the best thing to do is address the location of the floor inlet, and try some iterations of the diffuser design, which appears, as pointed out by everybody, to be too aggressive (see circulation, Balloon 3)... This would tend address the problem directly (the lack of rear-end downforce)....

I guess on your car variante, where you want to send air around the side pods, keeping the air flow horizontal is a definite plus... on the Brooke car with the lower and wider pods do you think keeping the airflow horizontal is the best thing to do (as opposed to trying to send it over the top of the pod)? do you think this might solve the re-circulation issue (balloon 2) which appears to be causing some lift in the middle of the car... (balloon 6)? I still worry this will lead to a lose of that precious front end downforce though... and we'll end up chasing our tail....

[andylaurence]

On a side note... I have been playing around with a CFD Model of a Hillclimb racer this weekend, and have managed to increase overall downforce by 42% just by adding flow conditioners/ vortex generators in the diffuser and upstream...

Which car is that? We're scanning the Mygale to get a decent model and will be modelling a new floor for it if anyone's interested in getting involved.

[variante]

I don't know whether it's legal in the competition (certainly it's illegal in LMP racing), but I wonder what the effect of aerodynamic skirts that extend to the ground would be on the underbody downforce. What arrangement would work best? Obviously it will depend upon underbody design, ride height, etc, but would it be better to allow cross flow from the sides of the car or better to completely seal off the underbody? I remember seeing an interview with the designer of the 956 who said that full body length skirts decreased downforce in that car. How about skirts that direct flow around the wheels to speed up underfloor flow?

Interesting question, No Lotus.

Just few hours ago Machin wrote about the necessity to increase airflow through the diffuser. That principle sums up, pretty much, the answer to your question.

It must be said, however, that pressure under the floor/diffuser has to be kept as low as possible. Letting "too much air" (let's read that as "airflows of indiscriminate pressures") inside that area could lead to lower downforce. Therefore any airflow coming inside the diffuser should be "conditioned" to the desired pressure (through, for example, Venturi channels).

Airflows coming from the sides are characterized by higher pressures, therefore they will decrease downforce.

Now, we've got three choices:
1. sealing the floor through skirts (which is illegal for KVRC, just like nowadays F1)
2. sealing the floor through vortices (which is a delicate, difficult task)
3. using the kinetic energy of the "intruder" flows to shed vortices inside the diffuser (which is what most of us are doing)

To answer more specifically to your question, skirts may be helpful, but in some conditions other solutions are more helpful... I think that the most helpful solution is actually both solutions combined in the smartest way (such as sealing some parts of the bodywork and letting air through other parts of it).

Fore example, I recently tried to put skirts on a Formula SAE car: the geometry of that car made skirts harmful to downforce production.
So, yeah...no solution is universal.

If you're interested in a more detailed answer, just tell us and we could arrange some simulations to prove the point and visualize.

[variante]

However, modifying the underside of the suspension fairing will likely lead to a re-loss of some of the front end downforce, which isn't exactly highly abundant as it is

Given the lack of strict regulations about front bodywork, very high levels of front downforce are easy to achieve. Using the front wing, rather that the suspension cover, to produce that downforce is a much more efficient solution. Also, the turbulences created by that cover are massive...they should not be tolerated...

...on the Brooke car with the lower and wider pods do you think keeping the airflow horizontal is the best thing to do (as opposed to trying to send it over the top of the pod)?

He can vent to the sides as much as i'm doing, if not more. Some upwash could be helpful to decrease drag generated by cooling inlets...but it must be a gentle and elegant upwash!

...do you think this might solve the re-circulation issue (balloon 2) which appears to be causing some lift in the middle of the car... (balloon 6)?

Definitely.

I still worry this will lead to a lose of that precious front end downforce though...

We've still got the double tier front wing option, right?

[machin]

Which car is that?

Its a secret project that has been on the back-burner for some time, it was intended to be a replacement for my Westfield Hillclimb/sprint car... but then I got hooked on cycling and then recently designing/building the Velox Time Trial bike (http://bicycledesign.net/2015/08/velox- ... rd-machin/).... one day I'll build the hillclimb car... (it is fully drawn up with a bill of materials and everything)... for now it provided a nice study to see how small changes can have a big impact: 49% increase in downforce without changing diffuser profile (there are no wings on the car, so all downforce comes from the underbody).

[machin]

...the turbulences created by that cover are massive...they should not be tolerated...

Do you not feel that the recirculation (balloon 2 in the last image above) is a result of the proximity of the leading edge of the floor in the upwash (the air is coming at that leading edge with some upward flow, and being a sharp edge it simply separates from the surface)... I would have thought that pulling that leading edge of the floor out of the upwash could actually increase front end downforce as well as the improving the rear end.... win win...

..Afterall, you haven't felt the need to go with a bi-plane upper front wing... that solution (the bi-plane upper wing one) to me seems more "sledgehammer" than "finesse"... covering over the problem as it were.....

[machin]

the turbulences created by that cover are massive...they should not be tolerated...

Perhaps this would be a neater solution...:-

[variante]

Do you not feel that the recirculation (balloon 2 in the last image above) is a result of the proximity of the leading edge of the floor in the upwash (the air is coming at that leading edge with some upward flow, and being a sharp edge it simply separates from the surface)... I would have thought that pulling that leading edge of the floor out of the upwash could actually increase front end downforce as well as the improving the rear end.... win win...

You're right: the separation is a consequence of that interaction. However I insist saying that, even with no separation, the action of that cover is destructive as it offers "wrong" AoA to the rest of the bodywork, decreasing pressure on top of all of it, thus generaing lift rearwards.

About front end downforce, i'm producing 2800N on the front axle (with the latest iteration of my car). I'm using the "upper wing" just to hide the front suspension, not for DF. So...no bottleneck on that side.

the turbulences created by that cover are massive...they should not be tolerated...

Perhaps this would be a neater solution...:-

Better

[RicME85]

Seeing as this is a joint venture Machin, what would you like me to do next?
Same geometry but change the cover to what you have suggested above? Or do you want the changes to the floor done at the same time?
I'd assume cover first then cover plus floor?

[No Lotus]

I don't know whether it's legal in the competition (certainly it's illegal in LMP racing), but I wonder what the effect of aerodynamic skirts that extend to the ground would be on the underbody downforce. What arrangement would work best? Obviously it will depend upon underbody design, ride height, etc, but would it be better to allow cross flow from the sides of the car or better to completely seal off the underbody? I remember seeing an interview with the designer of the 956 who said that full body length skirts decreased downforce in that car. How about skirts that direct flow around the wheels to speed up underfloor flow?

Interesting question, No Lotus.

Just few hours ago Machin wrote about the necessity to increase airflow through the diffuser. That principle sums up, pretty much, the answer to your question.

It must be said, however, that pressure under the floor/diffuser has to be kept as low as possible. Letting "too much air" (let's read that as "airflows of indiscriminate pressures") inside that area could lead to lower downforce. Therefore any airflow coming inside the diffuser should be "conditioned" to the desired pressure (through, for example, Venturi channels).

Airflows coming from the sides are characterized by higher pressures, therefore they will decrease downforce.

Now, we've got three choices:
1. sealing the floor through skirts (which is illegal for KVRC, just like nowadays F1)
2. sealing the floor through vortices (which is a delicate, difficult task)
3. using the kinetic energy of the "intruder" flows to shed vortices inside the diffuser (which is what most of us are doing)

To answer more specifically to your question, skirts may be helpful, but in some conditions other solutions are more helpful... I think that the most helpful solution is actually both solutions combined in the smartest way (such as sealing some parts of the bodywork and letting air through other parts of it).

Fore example, I recently tried to put skirts on a Formula SAE car: the geometry of that car made skirts harmful to downforce production.
So, yeah...no solution is universal.

If you're interested in a more detailed answer, just tell us and we could arrange some simulations to prove the point and visualize.

Thanks for your thoughts. I've sent you a PM.

[machin]

Seeing as this is a joint venture Machin, what would you like me to do next?
Same geometry but change the cover to what you have suggested above? Or do you want the changes to the floor done at the same time?
I'd assume cover first then cover plus floor?

Normally I 'd say do them in two steps... But this time I'd say do the cover and floor and diffuser in one go this time as they're all sort of related... The slices you gave us should be sufficient for comparison purposes to see what the changes have achieved....

[wesley123]

the turbulences created by that cover are massive...they should not be tolerated...

Perhaps this would be a neater solution...:-

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

Could a longer cover help in this area as a part of the issue is (i assue) caused by the direction of the airflow?

[RicME85]

I was wondering if having it so the cover went right back and met the leading edge of the sidepod would help?

Ive just noticed something with the current diffuser...its illegal its 33mm too high at the trailing edge. Oops.

[machin]

I was wondering if having it so the cover went right back and met the leading edge of the sidepod would help?

I'm not sure I understand... Maybe a sketch would show your proposal better?

The things to think about when making the changes:-

• What part of the current CFD analysis are you trying to resolve?
• what do you think the Pressures will be on the new/changed bodywork?
• what do you think will happen to the airflow downstream of the new/changed bodywork?
• How do you think this might affect pressures on downstream components?

[RicME85]

Just something as simple as this -


Ie a 'flat' top rather than having different aerodynamic devices to cover suspension and other parts of the car, have one overarching piece from front to back.

Have had AWS running for a good few hours with the front suspension and crash structure cover changes plus variante diffuser and new floor leading edge.