Category Archives: Exhaust Driven Diffuser
Analysis: 2013 F1 Rules and Trends
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With far reaching regulation changes coming onto the sport in 2014, the 2013 season is likely to be a year of consolidation, as few changes have been are written into this year’s rule book. So teams will be expected to optimise their designs from last year, correcting mistakes and adopting some of the better ideas of their rivals.
Some rules will have a small effect of car design and some trends from last year will be more common place. Unusually there have been few leaks or well-founded rumours circulating in the off season. This is probably as teams are expending a huge amount of resources in finding big gains for just one year’s competition, instead focussing on plans for 2014.
Mercedes: Downwashed-Exhaust Sidepod
After 13 races of the 2012 F1 season, Mercedes AMG have finally followed the trend of side exiting exhausts to blow the diffuser area. After low placed exhausts were banned for 2012, each of the top teams found methods to coerce the exhaust plume back down from the higher tailpipe. Notably Lotus and Mercedes did not follow this route, although at the Young driver test at Magny Cours, Mercedes were seen testing the McLaren style of sidepod.
Monza: Rear End Analysis
One of the most insightful views of an F1 car is from the rear. From this angle we can easily assess the amount of rear wing, cooling, exhaust position\effect, suspension geometry and important elements of aero\diffuser design. At Monza this weekend XPB images kindly allowed us to show these images, which clearly show different elements of some of the cars running this weekend.
Ferrari
The F2012 has followed its own aero philosophy, so it looks different to many other cars from the rear. For Monza specifically we can see the low drag rear wing, much shallower than the usual rear wing and with the “V” cut outs on the trailing edge. Also for Monza Ferrari cut down the beam wing, the small amount of drag the beam wing creates is reduced by slimming the outer spans of the wing, to reduce the tip vortices.
Ferrari’s sidepods are laid out differently to other cars, most of the cooling outlet area is on the flanks of the sidepods, through the Acer ducts and in the area of the tail of the coke bottle shape. So when we look at the car from the rear, the central tail funnel cooling exit is not present. This design may hinder flow in the coke bottle area, but does leave far more airflow to reach the rear wing. Additionally several cooling vents are made in the narrow bodywork around the gearbox.
Around the diffuser Ferrari have gone further than other teams, with the aero parts around the perimeter. Teams often fit gurney flaps or flaps at the diffusers trailing edge to lower the pressure behind the diffuser and encourage more air to pass through the diffuser for more downforce. In Ferrari’s case the diffuser now sports two flaps above the diffuser, one lower down and the larger one above. This larger one is clearly visible, the lower one is mainly visible through the arched shaping. Having a two element design to this flap means it can be angled more aggressively to have a greater aero effect.
Along with trailing edge the flap the tall flap formed under the crash structure has also gained a two element design. Evident in this picture is the starter motor hole, the end of the shaft that the starter motor engages with is clearly visible through it, but although the starter motor shaft is round the resulting hole is far from circular. Teams exploit the ruling for this opening, by making the hole a blow slot to improve airflow through the middle of the diffuser. Rules dictate only one hole must be used and of a maximum surface area. In Ferrari’s case their two holes are joined by a small slit to make them effectively one hole. Most teams exploit this area in one form or another.
Lotus
In comparison to the Ferrari the Lotus is a more conventional shape with the sidepods, although the exhaust position is evidently different. As Lotus are one of the most successful teams to race this year without a downwashed exhaust solution blowing the diffuser. In the case of Lotus the exhaust blows into the duct formed by the rear wing. Cooling for the E20 is largely exited through the middle tail funnel.
For Monza this wing is very small indeed, the reduced drag helping the Renault powered Lotus reach higher top speeds on the long straights of Monza. Unlike other cars described here, the Lotus beam wing is not waisted away and also retains the taller flap exploiting free bodywork zone the middle 15cm of wing span. Also interesting to note with the tidy rear end of the Lotus is the extreme convergence of the wishbones where they meet the gearbox.
There are two distinct features on the E20 diffuser exit; the side exits and the trailing edge flap. Lotus expands the diffuser not only upwards but also outwards, such that the diffusers exit passes sideways out of the maximum 1000mm width allowed for the diffuser. This increases the diffusers expansion ratio, for more downforce, the trick being keeping the airflow attached to the aggressively shaped diffuser walls. Above the trailing edge Lotus fit a flap in-between the rear wing endplates.
McLaren
McLaren is very similar to Lotus with the conventional sidepod and cooling arrangements, of course McLaren exploit different exhaust positions, with the side exiting exhaust being downwashed to blow the side of the diffuser. The central cooling funnel has been augmented by two small outlets near the cockpit. These sit just inside the free area for sidepod bodywork, any further outboard and they would be subject to the strict rules on openings and curvature in the sidepod bodywork.
McLaren run a low incidence Monza spec wing, but this is not as slim as some other teams. Likewise their beam wing is slightly revised with the outer tips eased off to reduce drag they create. Below this the diffusers trailing edge is treated to a flap around most of its perimeter and inside the diffuser large single opening for the starter motor is apparent.
Red Bull
The unique shape of the RB8 is apparent in this image, the sidepods blend into the gearbox and rear structure freeing up airflow to the diffuser and beam wing. This is possible because so much cooling flow is ducted out of the central tail funnel. Although for the heat of Monza extra openings are created in the lower flanks of the sidepod. Drag reduction is aided by the beam wing being shorn of its central peak. Resulting in a “V” shape dip in the beam wing. Below the tail light a small electronic device with cabling emerging from it is visible. This is the back up timing transponder. The primary transponder to signal to the timing system sits under the nose of the car. Being mounted in the position, the transponder is exposed to potential damage, so teams fit covers over the device to protect it.
Timing transponder position as described in the Appendix to the FIA Technical Regulations
The exhaust position is clear in this image, the exhaust outlets despite pointing upwards, is actually diverted downwards by the downwash over the sidepods and the coanda effect of the sloping tail of the sidepods. These effects deliver the exhaust gas to the edge of the diffuser for a greater sealing effect. This sealing effect is critical as the Red Bull runs the car with a high rake angle, which is a low front ride height compared to the rear ride height. We can see the edge of the diffuser is nearly as high as the rear wheel rim; this rim is about 15cm high, so with the 5cm under floor step the rear ride height must be near 10cm.
Similar to other diffusers, the RB8 also sports an arched diffuser with a trailing edge flap. However, Red Bull curves the flap downwards over the arched sections, this results in a small flat edge on the flap above the arch. Due to the way the carbon fibre is finished around these flats, they appear like openings from some angles and have been mistaken for blown outlets. Lastly Red Bull continues to use extended rear wing end plates that form vanes behind the diffuser. While other teams have used this design, they have raised the bottom of the vanes to only sit in the wake coming over the top of the diffuser, not coming out from under it.
Williams
Aside from their waisted gearbox creating nothing but open space ahead of the beam wing, Williams follow many of the principles seen on the other cars in this article. The rear suspension geometry can be clearly seen with the near horizontal top wishbone and far less convergence in the top\bottom wishbones compared the Lotus. While the steep angle of the driveshaft’s shows just how low the differential is placed. In this picture the lack of cooling outlets on the Williams is apparent and very different to the Red bull & Lotus who run the same Renault engine.
For Monza the beam wing has been dramatically slimed down to reduce drag on the straights. While the diffuser sports a trailing edge flap and tall curved vertical gurney under the rear crash structure. Like many teams William paint the cover of the rear timing transponder in fluorescent paint to make is clear to the rear Jack man to avoid it during hurried race pitstop.
Red Bull: Ducted Sidepod and Blown Starter Hole
Red Bull have raced two major iterations of sidepod and exhaust this season, at Valencia they introduced their third. This iteration brought the re-introduction of the bridgetunnel concept first used with their V2 sidepod. These sidepods not only sport a single tunnel, but the inlet is split to feed two different flows inside the bodywork. Initially mistaken as a double floor or double diffuser, This V3 sidepod sees a return to the duct blown starter motor hole raced in 2011.
Ferrari: Canadian GP Updates
Having revised their exhaust position throughout the opening races, Ferrari had found some stability with their Mugello package. However, for the Canadian GP the team brought what will probably be their definitive set up for the year. Like most teams Ferrari have followed McLaren’s practice of a exiting the exhaust pipe out of the side and housing it within a duct to help the flow to be redirected inwards and downwards towards the diffuser footplate. This solution diffusers from McLaren’s in several areas, but like other teams who have followed the McLaren exhaust set up, the differences are a pragmatic approach to save having to redesign the entire sidepod package. The team have also brought revised brake ducts, turning vanes and a Canada specific wing package to Montreal.
McLaren MP4-26 2011 – Fan Tail (Octopus) Exhaust
McLaren went into 2011 with an aggressive design strategy, this was a response to the poor initial form in 2010 and resulted in the dramatic “U” sidepods and a mysterious exhaust system.
It was this exhaust system that stole most of the column inches in the F1 press and the fan forums during pre season testing. One particular column fed the interest around the exhaust and christened it the “Octopus”. The article suggested the exhaust was ducted to several exits and used high temperature Glass Ceramic Carbonfibre (GCC). It went on to explain the unreliability of the exhaust solution was due to the heat making it fail.
It was true McLaren’s first tests, even from the first private shakedown runs before the public testing had started, demonstrated a problem with the initial exhaust design. But this exhaust solution was not the “Octopus” as described; in fact McLaren Technical Director Paddy Lowe explained to me at the 2012 cars launch, that “it didn’t look anything like an Octopus”. Adding “The exhaust we had was a slot, we called it a fantail”, which was a simpler, albeit still innovative solution.
Sauber: Exhaust Sidepod Development
Sauber have proven to be one of the more progressive teams with aero development this year. The team’s have played with several different approaches to aero and exhaust positioning over the opening months of the year.
Now Sauber have produced their fourth sidepod iteration and surprisingly it is a McLaren style exhaust outlet. This goes away from the path they forged with the ramped downwash sidepod. Aiding the new exhaust position is a revised vane over the top of the sidepod.
The team also ran a revised front wing. I will cover this development in a separate post.
Sauber launched their car with a simple sidepod (above); this almost looked like a Red Bull RB5 set up, with the top exit exhaust aimed generally over the rear bodywork. This simple initial attempt was probably just for the launch pictures.
As soon after, the definitive Melbourne spec exhaust was tested. This sported a distinctive ramped section, which created a downwash that drove the top exit exiting exhaust flow downwards, then the ramped tail of the diffuser encouraged the flow to follow the sidepods line down towards the rear tyrediffuser. This mix of downwash and coanda effect all but reproduced the EBD effect used in 2011. As the exhaust flow was directed along the bodywork, it appears to be more accurate way of directing exhaust flow towards the diffuser. However the effect lacks a path for the sidepods undercut airflow to pass through. Red Bulls Melbourne spec (V2.0) exhaust attempted to cure this with the cross over tunnel.
To aid the downwash flow over the sidepod Sauber added a horizontal vane over the front section of sidepod. This front 15cm of sidepod is free of the bodywork restrictions of the main sidepod volume. The vane points the airflow downwards, to drive greater flow over the exhaust exit. In isolation this vane actually creates lift, as is common with F1 aero this counter intuitive solution creates more global downforce because of its downstream effect, than the small loss in downforce its creates on its own.
In practice for subsequent races Sauber tried a third iteration of the exhaust, still with a top exit, but the exhaust faired-in and blow out through scalloped slot, presumably to better direct the airflow. Using similar interpretations of the exhaustbodywork rules as McLaren exploited with their side exiting exhaust. This V3 set up wasn’t raced and will probably never race, with this fourth version now seen in testing.
The V4 sidepod discards the philosophy of the firth three completely, instead the sidepod is shorter and the coke bottle area forms a much tighter waist. Protruding from the flank of the sidepod the exhaust sits inside a small bulged fairing. This fairing mimics the McLaren with the open topped channel cut in to it, to allow the downwash to redirect the exhaust flow. The channel probably also provides a small degree of coanda effect in bending the exhaust flow downwards, but far less than with the earlier sidepod designs.
Exhaust flow exiting the duct now passes openly towards the tyrediffuser intersection. With the coke bottle area now free of the ramped section, the undercut sidepod flow can pass towards the centre of the diffuser to use the energy in the flow to drive some downforce from the trailing edge gurney and starter motor slot.
With the change in sidepod profile and the exhaust exiting more sideways the through the top, the downwash vane has also been altered. Rather than a horizontal vane, the vanes curved around the frontal of the sidepod, to create the depression over the revised exhaust outlet position.
First sight: Ferrari Revised Mugello Exhaust
On Day3 of today’s Mugello test, Ferrari appeared with a major update to their sidepodexhaust configuration. Although at this stage it’s not clear if this set up is Ferraris definitive exhaust solution going forwards, or merely another interim set up.
What’s clear is Ferrari continue to follow their own path for exhaust and cooling flow. With the main cooling outlets being via chimneys exiting from the flank of the sidepod, a solution popularly termed the “Acer ducts”, due to the presence of the sponsor’s logo on the launch spec bodywork. With the launch car the exhaust exited through the rear exit of the ducts, and latterly the exhaust was moved to prevent overheating rear tyres and the duct cut away to allow more inboard location of the exhausts tailpipe.
Now the “Acer” ducts are brought more inwards and the exhaust exits over the top of the duct, periscope style. This suggests the exhaust is not being aimed at the floor at all, simply along the centre of the top bodywork towards the beam wing and the winglet mounted atop it. This would be less effective at creating downforce, but would be less sensitive to throttle position and have less of an effect on the rear tyre temperatures.
The floor and top body mouldings appear to new and quite large sections. This also suggests that the bodywork is going to change. Often with interim bodywork the panels are smaller to allow different shaped sections to be added. However the black heat shield panel around the exhaust is removable and may allow a switch to a McLaren style open-topped duct exit.
The continued presence of the vortex generator near the mirrors suggests some downwash effect is still being created, although the current spec is not really making use of it.
I will update this post as the test develops
Red Bull: Bahrain Sidepod Analysis
Having been slightly off the pace in the opening three races, Red Bull clearly do not have the RB8 working as they had expected. Pole position in Bahrain doesn’t prove their issues are over, but the car sports a revised sidepod set up this weekend and this has perhaps has unlocked the potential in the car. The new sidepods are a revision of the Version2 spec sidepod/exhaust set up. The Bahrain spec simplifies the sidepod, removing the complex crossover tunnel under the exhaust ramp.
Exhaust Versions
Sidepod Version1
At the cars launch the RB8 features a simple Version1 exhaust set up, aimed at being a benign solution to get the bulk of testing out of the way, without interference from complex exhaust issues. Then later in testing the focus could switch to the greater potential performance offered by the V2 set up. The V1 set up placed the exhaust in board and rearward, blowing under the top rear wishbone. The exhaust flux blew along the tail of the bodywork and under the beam wing. Despite suggestions at the time that this set up was a novel exhaust blown suspension set up; the solution was never intended for race use.
Sidepod Version2
Then on Day11 of the 12 day preseason testing schedule, the V2 sidepodexhaust appeared. A more complex solution than either the McLaren or Sauber set up, the sidepod aimed to both direct exhaust flow at the diffuser and route the sidepods undercut flow to the centre of the diffuser. To do this the sidepod had a more outboard and rearward exhaust position.
The exhaust blows down the tail of the sidepod, over a ramp made to try to attach the exhaust flow to the bodywork via a coanda effect to direct it in the correct gap between the rear tyre and diffuser. This is the same area the teams aimed their exhausts directly at last year. This area helps both seal the diffuser from flow blown laterally from the rear tyres and also the greater mass flow of the exhaust plume creates more flow through the diffuser, with both effects adding downforce. This solution follows the same path as the much applauded Sauber solution. Although the two systems were developed in parallel and RBR did not copy the Sauber after seeing it launch. The RB8 always was planned to run the V2 set up.
V2: a tunnel is created under the Exhaust ramp bodywork (yellow)
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V2: Flow from the sidepod undercut passes through the tunnel (yellow)
To keep the airflow passing over the top and centre of the diffuser, teams direct the fast moving flow from the sidepods undercut to this area. In Red Bulls case, the path of this flow is obstructed by the exhaust ramp and plume. To overcome this Red Bull have simply created a tunnel for the air to pass under the exhaust ramp and remerge towards the centre of the diffuser. This solution looks like is major aim was to direct flow to the start motor hole, an area exploited by ductwork on the 2011 RB7. Having more airflow passing into the starter motor hole, makes the hole act like a blown slot, making the airflow better up and under the middle section of diffuser for more downforce. Creating a crossover effect is somewhat like McLarens bulged exhaust fairing, that allow both the exhaust to be directed down to the diffuser edge by the downwash flow over the sidepod, but also creates a channel beneath the exhaust bulge to allow the undercut flow to reach the centre of the diffuser.
So it seems Red Bulls V2 floor make the best of the Sauber Coanda solution and the McLaren undercut solution.
What are the issues?
However this tunnel is compromised by the post-2009 area rules. Sidepod bodywork 50mm above the floor (actually 100mm above the reference plane) must meet tangential and minimum radius regulations. This means Red Bulls tunnel is limited to slightly less than 50mm in height, with a sharp top edge.
It seems it’s this crossover tunnel on the V2 sidepod that is an issue with the car. Recent flowviz tests in free practice were focussed specifically on the tunnel, as well as tests with an array of aero sensors trailing the diffuser in Bahrain. Also an insider tells me that the Red Bulls starter motor might not be creating the accelerating airflow into the steep middle section of diffuser that was envisaged. Instead the starter hole works better when blocked off. Perhaps this crossover tunnel is not flowing correctly to the centre of the diffuser and altering the accuracy of the exhaust flow towards the tyrediffuser intersection.
If the exhaust flow cannot reach the tyrediffuser gap accurately or perhaps more importantly consistently, then the driver will have a car that sensitive to throttle position.
Red Bull have been alleged to have clever engine mappings, cutting down to four cylinders at larger throttle openings at lower revs. This could either have the effect of a softer power delivery for better traction, of greater exhaust flow for more downforce at lower revs. Red Bull and Renault may still be finding ways to gain performance from exhaust mappings and these mapping have been investigated the FIA and shown to be within the regulations.
With several issues around the way the exhaust affects the cars handling, Red Bull said in China that the V2 sidepod was the potentially better solution, but the V1 set up gave Vettel more confidence. Horner admitted that it was possible to get the performance of the V2 with the feel of the V1. At Bahrain it appears that this is what RBR have done.
Sidepod Version 2.1
V2.1: With no tunnel the exhaust flow can pass without interference to the diffuser
These issues may explain the Bahrain sidepod upgrade. This new sidepod set up appears to be a rework of the V2 sidepod, most of the shape remains the same and the exhaust appears to be in the same position. So it looks like the moulds were altered to close off the cross over tunnel create a V2.1 sidepod.
With the tunnel closed off the issues complicating the exhaust and starter motor hole flow have been cleared up. But there still remains an issue with how the sidepod undercut flow reaches the rest of the diffuser. Sauber appear to manage this, but there still may be some potential airflow performance that is lost with this set up. Although the overall effect of an exhaust aimed accurately at the tyrediffuser gap may be a greater gain that that loss.
However with the tunnel gone there is a less complex route for the exhaust to reach the diffuser. With the exhaust flow better managed the intended exhaust effect will more consistent resulting in a better feel for the driver at different throttle positions and car attitudes.
V2.1: Slots in the floor aid the effect in sealing the diffuser
It’s notable that Red Bull have also reintroduced the slots in the floor ahead of the rear tyres, these haven’t been seen for a couple of years, their function is to inject some higher energy airflow into the gap between the tyre and diffuse. This, like the exhaust blown diffuser, offsets the sidewash (known as ‘Squirt’) created by the rear tyres impinging into the diffuser. Again this will all result in greater rear downforce.
If this is the first solution for Red Bulls woes, then it will be interesting how the team develop from the V2.1 sidepod. Perhaps the tunnel will reappear in revised form or a McLaren style solution will be tried.