2012: Exhaust Position and Blown Effects

For 2012 the technical regulations were partly released with the 2011 regs, but there are also some late additions to be published, mainly related to the efforts of the FIA to eradicate exhaust blown diffusers.
I have seen a draft copy of the exhaust positioning rules. These rules are still subject to change because of an ongoing Technical Working Group (TWG) discussion to refine the rules. Ross Brawn in particular has made comments about possible loopholes in these regs.
Looking at what has already been proposed, I do not think he was suggesting a loop hole to allow blown diffusers, but perhaps other areas where the exhaust could be blown to benefit aero.
Currently the exhaust rules are fairly open in terms of positioning, the main stipulation being only two exhaust exits are allowed. In 2010 we saw the Red Bull RB6 reinvent the concept of blown diffusers as a way of creating downforce from the exhausts. Since then every team has relocated their old periscope format exhausts, into low exiting solutions to blow the underfloor.

2012 Rules
For 2012 we will see rules which tightly dictate the position of the last 10cm section of the exhaust pipe.
Firstly the exhaust must only transfer fluids from the engines exhaust ports to the tail pipe exit. i.e. no other gasses can enter or exit the exhaust along any point in its length. This prevents any reinterpretation of the exhaust exit or one way valves to maintain exhaust gas velocity. As Ferrari have been believed to have run on their car this year.
Then the tailpipe section is tightly defined, the last 100mm must be a round thinwall circular section, of 75mm internal diameter with no obstructions. So oval tailpipes, or pipes with internal vanes andor slash cut exits are barred.
Then this last 100mm of pipe must be entirely within a specific area on the car. This has been highlighted on the accompanying drawings. The box seen in side elevation has to 500mm from the rear axle line and 250mm above the reference plane. This area is however very generous with a length of 700mm and height of 350mm. Thus the top of the exhaust could be as high as 600m above the reference plane, around the same height as the top of the rear tyres.
In plan view the box must be more than 200mm and less than 500mm from the cars centre line. So exhausts could not exit tightly placed along the cars centreline.
Within each of the boxes the exhaust must be positioned within a range of angles. From the side the exhaust must exit tailpipe-up and between 10 to 30 degrees from the reference plane. In plan view the tailpipe must be plus or minus 10 degrees from the cars centreline.

The red cones must not touch bodywork, the red area shows the range of where the exhausts could blow

Lastly the exhaust position is also controlled by ensuring no bodywork sits in the tail pipes wake. To measure this, an imaginary cone (diverging at 3 degrees) in line with the pipe, reaching as far back as the rear axle line must be drawn. This cone (drawn red in the illustrations) must not touch any bodywork, nor must bodywork be placed over the cone. With a typical F1 car the only bodywork in the regions behind the tailpipe are the rear wing endplates, the front portion of rear brake ducts and any central top bodywork (i.e. Red Bulls bulged central cooling exit).
Bodywork behind the rear axle can cross the cones path. Bodywork is defined as any sprung part of the car, so little can be done to deflect the exhausts plumes to reach a specific aerodynamic device.

2012 solutions
Without access to the as yet unpublished clarification on overrun engine mappings, it hard to be sure if it might still be beneficial for teams to blow bodywork for aero benefit. It may end up that it’s better to create an aero neutral exhaust position.

Aero Neutral
For a neutral exhaust position, a low & forward position within the allowable areas, blowing roughly in line with the line of the bodywork would make sense. This would follow the common approach teams used before EBDs.


For teams with low line gearbox solutions, blowing the exhausts into the void behind the engine above the gearbox may be beneficial in cutting drag. A ‘middle ground’ option could be blow towards the cars centreline above the rear impact structure, in most cases this would be fairly neutral, but the fitment of the winglet atop the crash structure for high downforce races would see it benefit from the exhaust plume.

Aero Benefit

To create an aero benefit we have to look at the influential bodywork at the back of the car, to see what could be blown advantageously.

Diffuser

Clearly it will not be possible to blow the diffuser, the forward and upwards exit of the tailpipe make the exhaust plume too high to interact with the diffuser anymore.

Beam wing

Blowing the beam wing is unlikely to be efficient

The beam wing is another possibility, this will be hard to blow with the exhaust positioning, perhaps the airflows downwash over the rear of the car could make it possible, but this doesn’t seem likely.
One possible help to creating more downwash of the exhaust plume towards the beam wing is the use of the suspension elements. The wishbones, push rod and track rod are unsprung and not counted as bodywork. Although they should be considered aero neutral, they are allowed to point up or down 5-degrees. If these elements were placed in the exhausts flows path, they could deflect the exhaust plume downward. In particular the rear leg of the top wishbone, which is already widely used a flow control device sitting high up in line with the top of the wheel and rear axle, could be used to drive some flow downwards to the rear of the car. Clearly any suspension element whether it be made of composites or titanium would need heat shielding to protect it from the +800c gasses

Rear wing

Blowing the tips of the top rear wing will add downforce, but may add a lot of drag

The upper rear wing is well within range of the exhausts especially in their higher position in side elevation. Teams could blow either towards the centre or towards the tips of the wing. Blowing the tips inboard of the endplates would create downforce, but also induce more drag from the vortices produced at the wing tip. So blowing the centre of the wing makes more sense.

Blowing the centre of the top rear wing will add downforce with less induced drag

Blowing the underside of the wing as opposed to blowing over it, should be most beneficial. Although the effect on the DRS may need to be better understood. As would any sensitivity to throttle, with the revised engine mapping rules. Practical issues of the wing being able to withstand the heat are not insurmountable, with wing sections made of Metal or with ‘Glass Ceramic Composites’ (already used for heat shielding). If the centre blowing of the top rear wing is used, we will some very high exhaust outlets. Either in tall fairings also acting as cooling outlets or sprouting from the side of the engine cover.

Brake Ducts

Blowing the rear brake ducts will add downforce directly into the tyres

Also blowing the rear brake ducts is an avenue worth exploring. The exhaust geometry doesn’t work quite so well in this area. Brake duct vanes, which we have seen proliferate over the past few years are allowed to be 120mm inboard of the rear wheel, roughly in line with the wheel and can protrude forwards the front perimeter of the tyre. But as some of the brake duct is ahead of the rear axle line there is less surface to blow on.
This might still be better than rear wing blowing, as the downforce is produced directly on the unsprung wheel, rather than passing through the suspension. The benefits of this over rear wing blowing would need a simulation to establish the better path.
Practicalities of heat shielding the rear brake ducts are already understood from EBDs which already apply of the exhaust plume over their surfaces. Also tricky would the positioning of the brake cooling snorkel, but again this is not insurmountable.

Drag reduction

Blowing outside the rear wing endplates will reduce drag

One leftfield idea would be blowing outside of the rear wing endplates. This would not produce downforce, but reduce drag. Just as we see slots in the endplate to reduce the vortices created at the wing tip. Blowing the exhaust would reduce drag when the exhausts are blowing hard. Theoretically when the car is in accelerating out of a turn or in a straight-line and needs as little drag as possible. The beauty of this idea is when the driver lifts off the throttle for a corner, even with limits on overrun mapping the slower exhaust plume would reduce its effect, increase drag again. This might be a less sensitive, but still effective position for the exhaust plumes. But its complications might not be worth the drag benefit.

Summary

What’s clear is we will see a variety of exhaust positions being tested and raced next year. Certainly the exhaust position we see on the launch car will not always be what we will see in Australia for the first race.

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