Trends 2011 – Exhausts and Diffusers

This year the technical talk has largely been about exhausts.  How teams have adapted to the ban on double diffusers and the added restriction on Exhaust blown diffusers. Just to aid understanding going into the new season, I have explained how these solutions work and how they look from beneath.

Double Diffusers

Force India 2010 Double Deck Diffuser (DDD)

Since 2009 the regulations regarding the floor have been interpreted in a literal sense to allow the double deck diffuser (DDD). Indeed the very same rules were exploited to a lesser extent under the previous rules, but this only produced small extra channels in between the outer and middle diffuser tunnels. With the major cut in aerodynamic aids for 2009, several teams sought to find a way to gain more expansion ratio from the smaller diffusers. In essence the loophole exploited the definition of surfaces formed between the step and reference planes. Multiple surfaces allowed fully enclosed holes, which fed the upper diffuser deck that sat above the 175mm lower diffuser. This allowed diffuser to be significantly larger in order to create more downforce. Notably Brawn, Williams and Toyota launched 2009 cars with DDDs. Other teams soon followed suit in 2009 and last year every car exploited the same loophole. Over the winter the FIA acted to close the loophole, by enforcing a single continuous surface across a 90cm span under the floor. In a stroke this banned the double diffuser, there being no scope to create any openings in the floor to feed the upper deck.

Single Diffuser

Double Diffuser


Exhaust Blown Diffusers
Another approach to regain lost downforce was the re-invention in 2010 of the exhaust blown diffuser (EBD). This used high energy exhaust gasses to blow the diffuser, the faster throughput of flow under the floor increased downforce. Two methods of EBDs were used in 2010, one blowing over the diffuser and the second blowing inside the diffuser. This latter solution was more effective at driving flow through the diffuser and created more downforce. However this necessitated a hole made into the diffuser to allow the exhaust gas to enter, I‘ve termed this method an ‘open fronted diffuser‘.

2011: No openings allowed in the yellow 90cm zone, outside certain holes are permitted

A by product of the 2011 rules intended to ban the DDD, also stopped this open fronted diffuser solution. However the rules enforced the continuous surface only across a 90cm width of floor and the diffuser is allowed to be 100cm wide. Thus a 5cm window was allowed each side of the diffuser.

Outer Blown Diffuser – Solution

Red Bull Diffuser: Flow passes under the outer 5cm of floor into the diffuser

Red Bull and Ferrari appear to have found this loophole simultaneously. Recently Sam Michael pointed out this was probably the most efficient way to blow the diffuser under the new rules. As Red Bull appeared with this set up first, its often termed the Red Bull Blown diffuser.

What these teams have done is to open up the floor 5cm either side of the diffuser, then route the exhaust towards this opening. The exhaust gas gets collected by the coved section of floor and this directs the high energy gasses under the diffuser, to recover some of the losses from the more open diffuser allowed last year.

Front Exit Exhaust

Renault Front Exit Exhaust: Flow passes wide around the floor before entering the diffuser

Renault meanwhile turned the problem on its head. As the aim of the EBD is to increase flow under the car, they pointed their exhaust at the front of the floor. I’ve had it confirmed to me by two ex-Renault sources that the exhaust does indeed mainly flow under the floor.

The exhaust pipe outlet sits above the step plane just ahead of the leading edge of the floor. This is not simply blowing out horizontally and across the floor, but is ducted slightly to blow downwards and backwards, this is roughly in line the with the flow trailing off the “V” shape above the splitter. Along with the strong vortices set up by the splitter, vanes and bargeboards, this makes the floor appear wider than it is. The flow will go out beyond the floor and then curl back in and under the floor. Some flow will inevitably pass over the floor, but the most of the energy will be driving more flow under the floor to the diffuser.

McLarens Slit Exhaust

The slit above the floor is visible. Copyright: Liubomir Asenov

No conversation about exhausts this year, would be complete without some speculation about McLaren. Amongst the several exhaust systems run by McLaren over the pre-season tests was a “slit” exhaust. This appeared at the first Barcelona test, but did not seem to appear for the second Cataluña test. The exhaust collector could be seen to duct towards a double thickness section of floor ahead of the rear wheels. This section was also interesting for its longitudinal slot, this slot was not large enough to be the actual exhaust outlet, This might be a cooling slot, or to improve the flow from above to beneath the floor.  I beleive the Exhaust is actually below the floor.  As when the car ran the same floor with a conventional exhaust outlet, there appeared to be a removable section of floor ahead of the rear wheels. Being just outside of the 90mm opening rule, the floor ‘could’ be opened to allow an exhaust to blow through to underneath. If sculpted correctly, the exhaust could be ducted back inboard and blow towards the diffuser from under the floor. It’s possible that this could be in interpretation of a legal opening, assuming it met the maximum fillet radius rules.
I’d expect the resulting exhaust outlets to be a long wide slot, this wider outlet would be needed to meet the maximum radius rules and also reduce the back pressure from the tight curve of the exhaust outlet. As the exhaust would have a tortuous bend, to curl back under itself to direct the flow inboard, rather than out wide around the rear tyre.

Mac Slit: The exhaust might exit beneath the floor in a long narrow outlet

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17 thoughts on “Trends 2011 – Exhausts and Diffusers

  1. Thanks for the great article Scarbs!
    To my untrained eye, the Renault solution seems to cover the most ‘area’ of the diffuser
    However since the exhaust gases has to cover a larger distance on the floor to reach it, would I be correct in saying that the exhaust gases aren’t as fast as the ones in other teams?

  2. I wouldn’t call the Red Bull exhausts a “loophole.” A loophole to me, is something that the FIA didn’t intend to allow in the rules.

    I think that that McLaren exhaust could be very effective if they can get it to work but it seems like it has a lot of reliability problems because of the floor melting and the differing vibrations of the exhaust / floor. I recall AndyATM from the autosport forums mentioning that McLaren were arguing that they need the PyroSic (or whatever they were intending to use) as part of the floor and not the exhaust but when they are merged together, I wouldn’t have any idea in which way the FIA would rule.

  3. Very nice article Mr Scarbs! Like many others on your blog!

    I think i’m going to click that “Donation” button! After all, you give so much more intels and details that in the magazines I pay for!

    You are doing an extraordinary work here! Keep it going!!

    By the way: how do you make these drawings? Photoshop I guess?

  4. From “Front Exit Exhaust”
    >>Some flow will inevitably pass over the floor, but the most of the energy will be driving more floor under the floor to the diffuser.

    May be there should be “more flow under the floor”?

  5. It seemed to me they do not have the opening, but I thought I was not seeing it.It seems that not using the opening they want exhausts to roll around the edge of the horizontal footplate of the floor and enter in the diffuser vortexing from below.

  6. Hi Scarbs, ¿What do you think about the Mercedes exhausts?. I have read that they could blow all the difuser, not only the exterior part like red bull or ferrari, and perhaps this is more efficient, I don’t know.

  7. Fabulous piece of analysis Craig!

    However, I’m still not sure I understand how the Renault solution works. Part of the reason for this is that I lack a clear idea of the airflow pattern between the trailing edge of the front wing and the front of the sidepods and floor.

    What I think you’re saying is that the vortices created by the horizontal splitter, vertical vanes and bargeboards, increase the effective width of the floor, and therefore its airflow capacity. But without sufficient airflow, this extra capacity would be under-utilised. Hence, the front-exit exhaust flow is designed to take advantage of this greater effective capacity?

  8. Hello Scarbs,
    Great blog for starters!

    About Renaults front exhaust: You mentioned earlier about Mercedes ‘half way exhaust’ that it is not so good as for example RB’s solution because of loss of exhaust energy. Doesn’t the Renault’s solution have same, or even bigger, loss of energy effect before diffuser?

  9. On Mclaen slit exhaust: I think they could work well even without bending to point downwards,as you suggest.
    If they stay like in the photo you posted, coanda effect and pressure gradient could make them curve abtubtly downwards around he floor lateral edge.

  10. Pingback: Renault – Front Exit Exhaust Details « Scarbsf1's Blog

  11. Craig,

    I realise it may be a bit early to tell, but if the Red Bull solution is the most efficient, does that mean that it’s the one that everyone else is wishing they’d thought of and working to copy (either for this year or for 2012)?

    And, re. your comment on Ferrari – any take on how much time that will give them, when they put the 5cm opening in?

    Thanks – awesome blog.

  12. I must say that I’m a bit confused as to how McLaren could have run the slit exhaust (blowing underneath the floor) if they had so wished. The Tech Regs basically don’t allow holes in the reference plane, step plane or vertical transition between them. The only way the slit exhaust could work is if it blows upwards in my opinion.

  13. Pingback: McLaren MP4-26 2011 – Fan Tail (Octopus) Exhaust | Scarbsf1's Blog

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