Analysis: Abu Dhabi Test – 2012 Exhausts

Image via Williams F1

Last weeks Young Driver Test was the first chance for teams to try exhausts systems designed to the revised 2012 rules. Next year teams will have to place the exhaust exits in a specific region of the car, with further restrictions on the pipes shape and angle. These changes have been introduced to ban the blowing of the diffuser for aerodynamic gain. While I have detailed these rules previously (http://scarbsf1.wordpress.com/2011/10/26/2012-exhaust-position-and-blown-effects/), we can start to look at what the teams have been doing in Abu Dhabi.

Three teams brought revised exhausts, most notably Williams who ran their exhaust in all three days of the test, while Mercedes did less running with their interim set up and Ferrari tried a non legal exhaust on just one of the testing days.

Williams

IR cameras point upwards towards the wing and pods on the wing house sensors (Image via Williams F1)

Shunning any running with an Exhaust Blown Diffuser (EBD), Williams ran in Abu Dhabi with an exhaust positioned within the correct area and orientation as demanded by the 2012 rules. Their exhaust is a simple interpretation of the new rules, with the exhaust placed close to the cars centreline and as rearwards as possible. Most interestingly the exhaust is tipped up at the maximum 30-degree angle. This positioning suggests the team are trying to blow the centre of the underside of the rear wing. While I have proposed more radical solutions in my previous article, this does show that teams are to look at blown rear wing effects, as opposed to purely aero neutral exhaust positions. Exiting the exhaust pipe at great speed and temperature, the exhaust plume will hit the underside of the rear wing. This would have the effect of speeding up the airflow under the wing decreasing pressure and creating more downforce.

Williams Exhaust is low and rearward within the legality zone (yellow) and points upwards at a max of 30-degrees

However this effect is more complex than a simple jet of gas hitting the rear wing. Gordon McCabe’s Blog (http://mccabism.blogspot.com/2011/10/exhaust-blown-diffusers-in-2012.html) highlighted some research by Prof. K. Kontis & F. L. Parra from the University of Manchester on the effect of exhaust gasses on an F1 car. They found the exhaust plume passing at an angle out into the airflow created its own drag and moreover was bent backwards by the airflow at greater speeds. When this theory is applied to the Williams set up of a steeply inclined exhaust pointed towards the wing suggests some very interesting effects come into play. Firstly at lower speed the exhaust plume (jet) will be far stronger than the flow over the car. Thus this jet passes upwards through the crossflow over the car, will reach the rear wing to create more downforce.

Jet in Crossflow - low speed: unimpeded the exhaust plume blows the rear wing

At lower speeds the jet obstructing the crossflow will create drag and there will be drag induced by the greater rear wing mass flow, but being at lower speeds this drag will not be detrimental to aero performance. Then at higher speeds when the crossflow over the car has more energy the exhaust jet will start to bend backwards. Most likely moving the jet away from blowing the wings under surface. Thus the blown rear wing (BRW) effect will reduce, the car will lose some downforce and the drag induced by the blown effect will also reduce. Thus at higher speeds the car will shed drag, further boosting top speed.

Jet in Crossflow: High Speed - the faster airflow over the car bends the exhaust plume downwards away from the wing

Williams Abu Dhabi Test exhaust is not a clear sign that they will have this exact positioning for 2012, but the test will have proven the blown effect and just as importantly provided data on the heat passed over the rear wing. It was clear that the rear wing was set up with numerous sensors for vibration, heat and pressure measurement. Many of these sensors were within the rear wing flap itself, the shear number of sensors run on the wing required two aerodynamic pods mounted to the rear wing endplate to house the wiring to send the data back to the onboard data-logger. Additionally Williams ran several different kind s of thermal cameras, mounted to the rear crash structure and pointed upwards looking at the underside of the rear wing. This would not only provide actual temperature measurement, but also highlight which areas are being blown by the exhaust, somewhat like a thermal flow-viz test.

Mercedes

Another one of the teams late to the blown diffuser in 2011 and in particular blowing the outer section of floor by the rear wheel, Mercedes also tried a non-EBD set up in Abu Dhabi. According to earlier comments by Ross Brawn on autosport.com (http://www.autosport.com/news/report.php/id/96276), the Mercedes test exhaust was not a definitive 2012 set up “”The car will be testing next week with our first interpretation of what the regulation will be.”, but merely a revised exit location to remove the exhausts effect from the rear ends aerodynamics, “This is compromised because we’re fitting it around the existing car, but we’re removing the effect of the blown exhaust to see how the car will work without that.”

The set up that Mercedes tested with was similar to Williams with the exhaust outlet focussed towards the innerrear of the regulatory box it needs to sit within. Flanked by bodywork the exhaust did not appear to be as steeply inclined as the Williams set up. Reinforcing Brawns comments about removing the blown effect.

Pictures in F1talks.pl gallery http://www.f1talks.pl/2011/11/17/ostatni-dzien-testow/

Ferrari

Like Mercedes Ferrari run an alternative exhaust on the last day of the test. However unlike these previously two teams they did not fit a 2012 spec exhaust. Instead the cars left-hand exhaust was routed dramatically sideways to exit ahead of the rear tyre. This set up would not be legal either in 2011 or 2012, but was probably a simple to completely remove the blown effect from the rear of the car. With the right hand exhaust apparently in its normal EBD set up, the team would be able to measure the difference in pressure left to right to access the effect the exhaust is having. While a large part of development for 2012 will be aimed at getting the exhaust to do some useful work elsewhere eon the car, such as a blown Rear Wing (BRW), the team salsa need to get the diffuser and rear brake ducts working without the artificially accelerated airflow blowing over the from the exhaust. As the test exhaust does not fit into the current regulations this test would be the one place where they could do this, with permission to run such an exhaust being unlikely for a Friday practice session. So although preparation is underway for their exhaust development, Ferraris plan for their 2012 remains hidden.

Ferrari: A Chamber has been added to the Exhaust system (yellow)

One area of Ferraris exhaust development that has recently been exposed is the exhaust chamber. These devices have been rumoured for many months. Most of the rumours attributed to Mercedes engined teams, although no evidence has appeared of the system on any of their three teams cars. As reported by Giorgio Piola at the Abu Dhabi race, Ferrari had this system in place for the Grand Prix and the system remained fitted for at least part of the test. What at first appears to be another exhaust outlet joined to the secondary exhaust pipe, is in fact a closed ended pipe. This picture of the exhaust removed from the car (http://www.f1talks.pl/2011/11/17/ostatni-dzien-testow/?pid=7210 via F1talks.plSutton Images), shows the large extension, which acts as a pressure accumulator when the exhaust is blowing. Then when the driver is off the throttle the pressure built up in the chamber is release, which smoothes the blown diffuser effect between full and partclosed throttle.

When on the throttle the chamber is pressurised along with the exhaust system

..

When off the throttle the chamber maintains some exhaust flow

Similar systems were common on Japanese 2-stroke motorbikes in the eighties, albeit placed on the inlet side of the engine (often termed ‘boost bottles’), Fords WRC car also featured a chamber on the inlet side for similar effect.

This system works on the backpressure created within the exhaust. It’s worth noting Ferrari have recently switched to the nozzle type exhaust outlets, these being narrower in cross section to that of the main exhaust pipe. Most probably these nozzles work to increase backpressure to smooth the exhaust plume at different throttle openings. Just as interesting is the switch of the Mercedes powered teams to nozzle type exits mid season, suggesting the exhaust chamber rumours may be true. It would be logical to assume that the back pressure created within the exhaust both by the nozzles and the chamber would affect top end power. But any time loss being made up by the less senstive aerodynamics.

In some respects this exhaust chamber is similar to what appeared to be a one-way exhaust valve fitted at several GPs this year. The belief being that the exhaust valve allowed the exhaust to suck in air when the driver was off the throttle, to maintain exhaust flow to the diffuser. This being a mechanical alternative to the off throttle mappings (Hot BlownCold Blown), which were to be banned mid season. There appears to be a move to again enforce engine mapping restrictions for 2012, so the teams will need to find ways to smooth the exhaust plume over the bodywork. But this one-way exhaust valve will be expressly banned under the 2012 Exhaust Regs. So the exhaust chamber solution appears to be a design what will become present on the many cars exploiting blown exhaust effects in 2012.

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