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TECHNOLOGY – BLOWN FLOORS


High-performance thermal barrier coatings, such as ThermoHold from Zircotec, are playing a major part in this particular area of aerodynamic development. Shown here is an exhaust outlet with a ceramic coating


very strange things. The radius and the contact patch changes continuously, and this is a very important aspect in terms of aerodynamics, especially in open- wheel cars. At the base of the tyre there is a vortex created and, if this gets into the diffuser, it reduces its effectiveness. Using the mass flow from the exhaust to drive this vortex away from the diffuser and other critical areas effectively makes the diffuser larger and more efficient.’


COMPUTER SAYS ‘NO’ But to fully understand these flows is a complex challenge, only really made possible by recent technological advances. Indeed, when van Rees attempted to run his first simulations he discovered it required more computing power than the clusters at Cranfield could supply, so he was forced to simplify his model. ‘One of the important things


to remember is that the exhaust is a very high temperature gas flow, and you have to manage


that in the simulation,’ explains van Rees. ‘To do it fully, you have to understand the changes of the properties of the gases. The velocity, density and the thermal conductivity are all influenced so, for me, CFD was really the only way to survey all these factors.’ Van Rees’ simulation was basic by current F1 standards, but nonetheless highly revealing, and he found substantial gains to the aerodynamic performance of the Pilbeam. ‘Just using a very rudimentary design, the MP98’s downforce increased by 11 per cent, and more detailed studies could almost certainly bring greater gains. The drag level also increased but, even so, there was an overall gain.’ With the widely reported change in Formula 1’s exhaust regulations often called a ban on blown diffusers, many of the innovative layouts, such as those used by Red Bull, were outlawed. However, blown diffusers are not banned per se, and the teams are still actively trying to optimise


their exhaust plumes. ‘It is still important, but when you have changes in performance of the order of magnitude that we are seeing with the tyres and getting the tyres to work, it’s not our higher priority,’ explains Ross Brawn of Mercedes. ‘Last year it was one of the predominant performance factors, but this year it is nothing like as significant as it was. I think the cars that came first and second at the Spanish Grand Prix had very conventional exhausts so, unlike last year, the cars with innovative positions are not pulling away from those who are conservative. The range of performance between the solutions is much smaller now. But we still do a lot of work on it, both in CFD and tunnel testing. You can’t do everything in a wind tunnel and, obviously, you cannot generate hot gas. It’s a combination of both that gives the best results.’ Indeed, most modern F1


teams are now working on simulating exhaust flows in the


wind tunnel, but it is notoriously difficult to do, as Giorgio Ascanelli, technical director at Toro Rosso, admitted in pre- season testing: ‘Our simulation capacity is limited in this respect. It depends on the pulse, the speed of exhaust flow compared to the speed of the airflow, the expansion rate, the temperature, ride height, cornering speed and we cannot simulate all of these things with sufficient certainty.’


THE TMG CONNECTION However, some wind tunnels are more advanced in this respect, and Toyota Motorsport GmbH (TMG) in Cologne is a popular destination for Formula 1 teams chasing aerodynamic gains, partly because both of its wind tunnels are capable of simulating exhaust gases, as engineer, Chris Herbert, explains. ‘We have two systems at TMG. In wind tunnel one, we use an air amplifier inside the model connected to a compressed air line. In wind tunnel two, as part of the wind tunnel assembly,


“exhaust is a very high temperature gas flow, and you have to manage that in the simulation”


68 www.racecar-engineering.com • July 2012


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