Ground Effect Tunnel Designs

[OO7]

I was of the impression that while it hasn't been CFD tested, it was created by engineers based on fundamental aerodynamic principles (excluding the plasma field ).

Trust me, no aero engineer was involved in the creation of that thing, nor any proper designer...

Anyway, placing the floor as low as possible, even at a constant ride height, doesn't necessarily give you more downforce. In fact, besides sensitivity to ride height variations, another reason for the raised floor could be the presence of a thick boudary layer. Thus, that floor height could be a tradeoff between Venturi effect and boudary layer thickness (and ride variation sensitivity as well).

In particular, if the ride height is equal to or smaller than boudary layer thickness, downforce will decrease and the floor+diffuser system would be more likely to stall.

A commonly adopted solution to decrease boudary layer thickness, energizing the airflow (which gives you better chances to exploit Venturi effect) is generating vortices at the leading edge of the floor. Those are created thanks to bargeboards or similar devices (one of the few good things about that McLaren concept is that it shows such vortex generating devices under the leading edge of the floor).

So generally speaking, would the characteristics of the boundary layer be a function of the front end design of the car, namely the design of the front wing?

[OO7]

Yes, I considered that ride height sensitivity could play a part, but noticed that no pre-1993 IMSA GTPs (prior to the mandated flat floor section under the driver) were designed with raised tunnel throats. There is a video interview with the designer of the Porsche 956, where he stated that unlike single seaters, it was necessary for the throat of the tunnel in this specification of car, to be fed from airflow along the sides of the car. That simply feeding from air entering under the nose had pretty much no impact. Perhaps this may be one of the reasons that a lower throat was necessary?

It's difficult to speak to a designer's intentions with regard to underbody flow in the early '90s, because the subject wasn't particularly well understood at the time - and it remains the least understood piece of the puzzle today.

My best guess is that the IMSA guys were perhaps exploring force enhancement from edge vortices to varying degrees - overview below - while the F1 guys were busy with active suspensions. But, that's just a guess.

http://i.imgur.com/tqVuLED.jpg
From Ground Effect Aerodynamics of Race Cars

http://i.imgur.com/dtbQU0c.gif

Thanks bhall. That excerpt from Xin Zhang's study actually managed to answer some of my questions on the fly, pertaining to skirts.

When Norbert Singer mentioned that airflow needed to come from the sides, I didn't considered the connection with vortex generation along the side of the tunnel. I assumed he was referring to a wide throat with its outer edge placed at the cars maximum underbody width, so the flow is encouraged into the tunnels via the side of the tunnels throat.
Like this.........:



..........rather than this:
(This is a model of the 962 underbody, which is very similar to the 956s)


Also interesting are the smooth transitions from the wall to ceiling of the Nissan P35's tunnels.........:




.......These would seemingly contradict/mitigate the concept of vortex generation, however an elegantly sculpted strake has added for that purpose one would imagine.

Incidentally, that highlights the misnomer of exhaust-blown diffusers, especially designs from 2010 to 2013. The concept was never intended to "seal" the floor; rather, exhaust gasses were used to energize edge vortices, which allowed for more aggressive diffusers and rake angles.

I think the "specialized press" was way off on that one.

http://i.imgur.com/n9RybKq.jpg

http://i.imgur.com/BIet568.jpg

There does appear to be quite a significant difference in rake between the Mercedes W04 and the W05 - W06, with 2013 car exhibiting the greater angle.

As for McLaren's design study, it just looks like a funky, highly stylized double-diffuser to me. Air flow would be accelerated by the floor's curvature and turning vanes around the leading edge before being extracted by the secondary diffuser at the rear of the car. If effective - big if - it would just move the floor's aerodynamic center to an area that's closer to the middle of the car.

Do you mean the area circled here:

[OO7]

This is an interesting piece:
https://www.linkedin.com/pulse/how-do-m ... plash=true

It is a nice article and I hope he goes into a little more detail about some of the designs and methodologies used in the F1 cars he worked at some point.

[OO7]

The IMSA GTP regs in the late 80's were wide open. They allowed GTP cars to compete with Group C cars. And GTP cars could run at various combinations of engine type and weight. Some of the undertrays used on early GTP cars had massive tunnels. I believe the IMSA GTP regs in the late 80s/early 90s limited the tunnel height to 18 inches. The group C cars later on were required to run much smaller diffusers.

http://trackthoughts.com/wp-content/upl ... 00-013.jpg

riff_raff, the IMSA GTP series began to limit tunnel height in 1993. For Group C I think it was 86 or 87.

[bhall II]

These [smooth surface transitions] would seemingly contradict/mitigate the concept of vortex generation...

Not at all. A vortex forms any time a stream from a low-pressure area merges with one from a high-pressure area, and static pressure directly beneath the kink line (throat) of a diffuser will always be lower than static pressure in the area adjacent to it.

Any diffuser geometry that increases the dynamic pressure of air flow under the floor will also reduce static pressure. Therefore, any diffuser geometry that increases dynamic pressure will also create stronger edge vortices.

The edge vortices that form in a diffuser are more or less identical to the edge vortices that form under an inverted air foil equipped with end plates - like a front wing. It's a feature of ground effect.

Do you mean the area circled here:

No, here:



Look familiar?

[variante]

I was of the impression that while it hasn't been CFD tested, it was created by engineers based on fundamental aerodynamic principles (excluding the plasma field ).

Trust me, no aero engineer was involved in the creation of that thing, nor any proper designer...

Anyway, placing the floor as low as possible, even at a constant ride height, doesn't necessarily give you more downforce. In fact, besides sensitivity to ride height variations, another reason for the raised floor could be the presence of a thick boudary layer. Thus, that floor height could be a tradeoff between Venturi effect and boudary layer thickness (and ride variation sensitivity as well).

In particular, if the ride height is equal to or smaller than boudary layer thickness, downforce will decrease and the floor+diffuser system would be more likely to stall.

A commonly adopted solution to decrease boudary layer thickness, energizing the airflow (which gives you better chances to exploit Venturi effect) is generating vortices at the leading edge of the floor. Those are created thanks to bargeboards or similar devices (one of the few good things about that McLaren concept is that it shows such vortex generating devices under the leading edge of the floor).

So generally speaking, would the characteristics of the boundary layer be a function of the front end design of the car, namely the design of the front wing?

Yes, a function of front wing design, as well as any other piece of bodywork. But also a function of bodywork surface.

[OO7]

These [smooth surface transitions] would seemingly contradict/mitigate the concept of vortex generation...

Not at all. A vortex forms any time a stream from a low-pressure area merges with one from a high-pressure area, and static pressure directly beneath the kink line (throat) of a diffuser will always be lower than static pressure in the area adjacent to it.

Any diffuser geometry that increases the dynamic pressure of air flow under the floor will also reduce static pressure. Therefore, any diffuser geometry that increases dynamic pressure will also create stronger edge vortices.

The edge vortices that form in a diffuser are more or less identical to the edge vortices that form under an inverted air foil equipped with end plates - like a front wing. It's a feature of ground effect.

Do you mean the area circled here:

No, here:

http://i.imgur.com/d1PabxP.jpg

Look familiar?

I bolded the wrong part of your post, but I think I understand what you mean. The second low pressure zone situated at the front edge of those flat plates ahead of the rear wheels, they would behave in a manner similar to the double diffusers of yesteryear.

Would you say that generally speaking, vortices formed from abrupt transitions are more powerful but less stable, than those created from surfaces with smoother more gradual transitions?

[riff_raff]

riff_raff, the IMSA GTP series began to limit tunnel height in 1993. For Group C I think it was 86 or 87.

The IMSA P cars with their huge underbody tunnels had to deal with the high-speed banked turn at the Daytona 24 hour race. Very hard on the tires.

[FW17]

How did the sport cars keep the floor sealed without skirts or vortex generators?

[Just_a_fan]

In Group C, no one seemed to bother with floor sealing until Southgate designed the XJR-8. He made the bodywork slightly narrower than the maximum permitted and then had an outward facing lip, a gurney flap if you like, at the bottom of the bodywork. This improved the underfloor performance compared to the previous sharp corner bottom of the bodywork.

[Andres125sx]

In Group C, no one seemed to bother with floor sealing until Southgate designed the XJR-8. He made the bodywork slightly narrower than the maximum permitted and then had an outward facing lip, a gurney flap if you like, at the bottom of the bodywork. This improved the underfloor performance compared to the previous sharp corner bottom of the bodywork.

A picture is worth a thousand words

[toraabe]

Groundeffect at it's best.
And I have to admit. why on earth is this not allowed in F1 ?
Let the floor design be up to the team. Should have been totally free.
So maybee laptimes 10 seconds faster in Melbourne than today......

In Group C, no one seemed to bother with floor sealing until Southgate designed the XJR-8. He made the bodywork slightly narrower than the maximum permitted and then had an outward facing lip, a gurney flap if you like, at the bottom of the bodywork. This improved the underfloor performance compared to the previous sharp corner bottom of the bodywork.

A picture is worth a thousand words
http://www.f1fanatic.co.uk/wp-content/u ... d-2012.jpg

[OO7]

riff_raff, the IMSA GTP series began to limit tunnel height in 1993. For Group C I think it was 86 or 87.

The IMSA P cars with their huge underbody tunnels had to deal with the high-speed banked turn at the Daytona 24 hour race. Very hard on the tires.

I can imagine! The 1992 Toyota Eagle MKII had a relatively conservative tunnel diffuser design, that was at the same height as the drive shaft. The 1993 MKIII continued with this design after the regulations restricted the height of the tunnels, yet in the quest of evermore performance and the inevitable aerodynamic advancements, the 1993 car produced significantly more downforce than its predecessor.

[OO7]

How did the sport cars keep the floor sealed without skirts or vortex generators?

In Group C, no one seemed to bother with floor sealing until Southgate designed the XJR-8. He made the bodywork slightly narrower than the maximum permitted and then had an outward facing lip, a gurney flap if you like, at the bottom of the bodywork. This improved the underfloor performance compared to the previous sharp corner bottom of the bodywork.

The dive planes helped with this also, as explained here:http://www.mulsannescorner.com/nissangtpzx-t-5.html

[NOT A TA]

Groundeffect at it's best.
And I have to admit. why on earth is this not allowed in F1 ?
Let the floor design be up to the team. Should have been totally free.
So maybee laptimes 10 seconds faster in Melbourne than today......

Back in the early 90's most sanctioning bodies decided that limiting under body aero would be safer. When down force is lost due to some mechanical failure like a stuck sliding skirt, flat tire, etc. or turbulence from a leading car the effect is almost instant.

Here's one example I remember.

https://www.youtube.com/watch?v=g8XxQkXCmsU