[WEC 2015]Nissan GT-R LM NISMO

[machin]

Agreed... But the Audi effectively has a front diffuser that is "driven" by the adjustable flap... It has rather a lot of volume.... Whereas the space under the gearbox on the nissan looks rather flat and restrictive and without (apparently) the secondary flap to drive it...

Interestingly, almost this exact concept (front engine, front wheel drive, with diffuser throat under the engine/transmission and with long tunnels unobstructed by a rear transmission exiting out the back of the car) was proposed by Simon McBeath in the book "Competition Car Downforce", which must be getting on for 20 years old now...

[RacingManiac]

The area under the gearbox is just central portion of the floor though, in a normal car its also obstructed not much differently since thats usually where the tub is. Look at width of the gearbox section where suspension mounts to its really no different than your regular MR LMP1 cars



Yes the immediate area behind that is a bit more cramped, but the normal LMP also at which point the flow has to make a turn and out the side or enters the sidepods for rad.

This pic that Blanchimont posted is interesting too:



You got to assume that space in front of the carbon "arch" under the turbo is basically open for the diffuser flow, which opens out into that void that will exist between the outside edge of that arch and the tub itself, pretty much unobstructed to the back of the car.

I am still curious if they can turn the exhaust into the tunnel...not sure if that'll help anything....

And that RP gearbox shows a hole right by where the front rocker pivots, maybe for a 3rd element for the front suspension?

[DaveKillens]

All good points RacingManiac. It is very possible that the suspension and turbo exit could receive further "upgrades". IMO what we are seeing is a proof-of-concept, the basic package will be tested, and once the numbers start to line up, then the team can explore alterations that may be of benefit.

As we all know from observing Formula One, when you introduce a completely new power unit package, theory and practice may not be the same animal. Getting 8Mj out of the KERS will be a tall order, getting the transmission to allocate torque to the correct outputs at the right time will be "interesting". There is a lot to be sorted out before additional performance options are explored. Just look at the cutouts over each wheel, they will be partially or completely blanked off the balance the aero load on the car.

But it sure is wonderful to explore something that is definitely not traditional, something that challenges all of us to understand.

[machin]

It is definitely making me seriously think about a trip to Le Mans this year...

Racecar Engineering Magazine (March issue), has an article which claims they're aiming for 2 or 4 MJ, which seems to contradict some of the articles on the web...

[matt21]

Has anybody a clue what the two pipes coming from the center part are for? Feeding ducts fur the turbos?

[Blanchimont]

Yes, these pipes are for providing air to the engine. In the picture you can see the fitting of a pipe towards the compressor. What a great pr strategy to publish such pictures! Thank you, 23!

https://www.flickr.com/photos/nissan-racing/sets/

[machin]

I think this is an interesting comparison of the space available at the front ends of the Nissan and Audi... Remember the Nissan, with its front weight bias, needs to generate more front downforce than the Audi to have equal performance...



The question is; do those nice clear tunnels running to the back of the car make up for what appears (to me at least) to be a smaller front diffuser volume....? I certainly don't know but am fascinated to find out!

Also, I'm loving the fact that Nissan have released all these photos for the fans... I like the ones of the car without the bodywork... you can see that it is rather like a Deltawing in reverse (without the narrow track at the non-engine end of course!)...

Interestingly I saw Ben Bowlby give a talk on the Deltawing a few years back (when it was first released to the public) and he said that he had originally thought about putting the heavy/wide end at the front, and the reason he didn't was because of the acceleration effect losing traction on the driven wheels... of course, the fact that this thing has AWD means that problem effectively goes away...

[Blanchimont]

Another picture showing the pipes to the compressor and the diffuser below the lower front suspension arm.

[Blanchimont]

The question is; do those nice clear tunnels running to the back of the car make up for what appears (to me at least) to be a smaller front diffuser volume....? I certainly don't know but am fascinated to find out!

For me the important thing is the expansion ratio of the diffuser, not so much the cross section at the front. If cross_section_front/cross_section_rear is big enough(what it seems to be), then the pressure should be low at the front axle part. Let's hope Nissan is that open to publish some aero figures and CFD results in the future.

[machin]

. Let's hope Nissan is that open to publish some aero figures and CFD results in the future.

That would be awesome... but do we have similar figures on the Audi/Porsche/Toyota?

below I have marked up what I think is the difference in the tunnel size at its most restricted point on the car (I've had to guess somewhat with the Audi because the sidepod bodywork gets in the way on the photo obscuring the reduced height section under the tub).... Although as you say, the expansion ratio is potentially a lot better on the Nissan...

[antrock]

Without bodywork.

[matt21]

I just had a quick look in the regulations.

Article 11.1 is stating:
No transmission system apart from the MGU(s) may permit more than two wheels to be driven.

Does this imply that you have to choose permanently which wheels are driven by the ICE or does it mean that only two wheels can be driven at a time?
If the last is correct you can switch between front and rear drive depending on the actual behaviour of the car.
You have to overcome the "only-one-clutch-rule" then but maybe with a visco-coupling?

Another article which could be intressting is this one:
11.5 Torque Transfer Systems
11.5.1 Any system or device the design of which is capable of transferring or diverting torque from a slower to a faster rotating wheel is not permitted.
11.5.2 Any device which is capable of transferring torque between the principal axes of rotation of the two front wheels is
authorised providing that it remains passive.

In my opinion this allows a kind of fiddle-brake-system like McLaren had. Would this be of any use?

[RacingManiac]

I feel like the wording MGU is kinda going to allow some fudging, since, if the flywheel are "driven" by the front wheel's torque through the transmission(normally under braking), and that is essentially what MGU is to the flywheel in this case(flywheel being the battery of sorts) and the engine can drive the the front wheel, and the flywheel can drive the rear wheel, then if you connect all the dots you are driving the rear wheel with the engine, even though technically its the flywheel doing it.

I mean the Flybrid system has its own gearbox for the flywheel to match speed as needed, if the speed equalizes you are basically directing drive torque directly to the back no?

Unless there are rule specifically prohibits you from engaging ERS on power?

[PlatinumZealot]

I just had a quick look in the regulations.

Article 11.1 is stating:
No transmission system apart from the MGU(s) may permit more than two wheels to be driven.

Does this imply that you have to choose permanently which wheels are driven by the ICE or does it mean that only two wheels can be driven at a time?
If the last is correct you can switch between front and rear drive depending on the actual behaviour of the car.
You have to overcome the "only-one-clutch-rule" then but maybe with a visco-coupling?

Another article which could be intressting is this one:
11.5 Torque Transfer Systems
11.5.1 Any system or device the design of which is capable of transferring or diverting torque from a slower to a faster rotating wheel is not permitted.
11.5.2 Any device which is capable of transferring torque between the principal axes of rotation of the two front wheels is
authorised providing that it remains passive.

In my opinion this allows a kind of fiddle-brake-system like McLaren had. Would this be of any use?

This ruling means that electronice torque vectoring differentials are not permitted.

[Artur Craft]

Diffusers deliver a great percentage of the total downforce for a Formula One, or LMP car. Wings are nice, but diffusers are much better.
What is the best way to extract the air from the diffuser, dump it out the sides where there is some negative pressure but a lot of turbulence, or duct it to the very rear where it is subjected to very low air pressures?

There is almost no turbulence on the sides of the cars(from CFDs I have seen) whereas there will be some on the back.

The question is; do those nice clear tunnels running to the back of the car make up for what appears (to me at least) to be a smaller front diffuser volume....? I certainly don't know but am fascinated to find out!

For me the important thing is the expansion ratio of the diffuser, not so much the cross section at the front. If cross_section_front/cross_section_rear is big enough(what it seems to be), then the pressure should be low at the front axle part. Let's hope Nissan is that open to publish some aero figures and CFD results in the future.

My take on the discussion of GT-R LM front diffuser is that it will likely either failure massively or start a trend.

Reasons: There is quite a big cross section at that diffuser exit but the "mouth" feeding it provides space for much reduced air volume to enter the channel/duct system. From my experience,(studying it at college and the many fluid dynamics books read since, plus CFD and wind tunnel results that I have seen) there is quite a good chance that this will, at least partially, stall(air will not flow within the ducts but rather get's stucked in there) it and the downforce will be very small.

Plus, because the mouth is also the same for the rear diffuser(which is just under the frontal one and effectivelly both being just one giant diffuser supposed to generate downforce at both axles), the air entering the frontal underside of the car also needs to flow to the rear diffuser in order to not stall it.

I think there is just too much of a difference between the amount of air that get's through the "entrance" and the "exit", of the whole underbody channels, in order for it not to stall. BUT, maybe I'm wrong, as maybe(don't remember exactly now) the ground effect cars had that big difference too and it worked.

To increase their odds, I think it's better for them to do all they can to blow in that ducts, as exhaust gases, at very high speeds, can help push/expel all that air out.

If they get it flowing, it will generate very big downforce levels because the air will be moving at much higher speed(compared to the competitors' solution) as it would need to do so, in order to fill the gap of that bigger exits, once relatively little air get's in.