Thursday 12 May 2011

Audi R18 TDI with efficient aerodynamics

Audi R18 TDI with efficient aerodynamics • Only four weeks before the 24 Hours of Le Mans • Impressive maximum speed despite reduced engine power • Innovative engine concept also brings aerodynamic advantages

Ingolstadt, May 12, 2011 – Audi contests the famous 24 Hours of Le Mans with a
closed car for the first time since 1999. Aerodynamic efficiency was the focus of
attentions during development of the new Audi R18 TDI because it plays an even
larger role at Le Mans than in the past.
“A closed car is not necessarily more efficient,” stresses Dr. Martin Mühlmeier, Head
of Technology at Audi Sport. “Race cars designed to generate very high downforce
levels, in Formula 1 for example, are also very efficient ‘open’ designs. If you want to
go in the direction of low drag or must, like now at Le Mans with the engine power
being reduced and the circuit characteristics still dominated by long straights and
high speed, then a ‘closed’ car is more efficient than an ‘open’ one.”
For this reason, Audi Sport has dropped the ‘roadster’ concept with which the four
Rings brand recorded nine Le Mans victories between 2000 and 2010. Head of Audi
Motorsport Dr. Wolfgang Ullrich has mixed feelings: “I really liked the ‘open’ cars
but there are beautiful ‘closed’ sports prototypes as well – and I think that the R18
TDI is a typical Audi making a very good visual impression.”
It is, however, not only aerodynamic efficiency that plays a role in the decision for or
against a ‘closed’ car. The sporting regulations developed in such a way over the
years that one of the roadster’s decisive advantages – namely fast driver changes –
was eradicated: changing tires at Le Mans now takes considerably longer due to the
fewer number of mechanics allowed to work simultaneously on the car. Therefore a
fast driver change is no longer a decisive factor.
Turbulence in the cockpit area is the greatest disadvantage ‘open’ race cars have
with regard to a good cd value. Airflow around a closed car like the R18 TDI is
significantly more uniform. The resulting increase in aerodynamic efficiency can be
transformed into either more downforce or greater top speed.
The wind tunnel continues to play a major role during the development of a Le Mans
sports car. The relevance of so-called CFD (Computational Fluid Dynamics)
simulations on high-performance computers was increased significantly. CFD allows
engineers to simulate the air flow around and through the car. “While basic
concepts and also complex detail tests are calculated, performance relevant
dynamic running conditions can be evaluated in the model wind tunnel,” explains
Axel Löffler, Head of Chassis Development and Aerodynamics at Audi Sport.
Optimization of the aerodynamic efficiencies in different dynamic attitudes was one
of the most important points in the R18 TDI performance specification. “The ground
clearance changes, at high speeds the car is closer to the track due to the
downforce,” says Mühlmeier. “Once again our target was to achieve well-balanced
handling that is not too acute. To a certain extent you must forego absolute peak
values to realize this.”
In contrast to the preceding R15 TDI model, the internal airflow of the car could be
significantly improved. The innovative engine concept is, among other factors, also
responsible for this. The extremely compact V6 TDI engine and the relocation of the
exhaust system and turbocharger to the top of the power unit allows hot air exiting
from the coolers to flow unobstructed out of the rear bodywork.
The fin, stipulated by the regulations, which extends between the cockpit and rear
wing and which should help to reduce speed in the event of a spin, had considerable
influence on the design of the R18 TDI. “Integration of the new fin in the overall
vehicle aerodynamics was the result of extensive analysis,” says Axel Löffler. “To
respect the safety aspects without creating losses in the overall efficiency required
completely new approaches during development.”
As a consequence Audi Sport tried to integrate the fin into the vehicle’s structural
and overall aerodynamic concept. To this end, the rear wing mountings merge
almost seamlessly with the fin. The single piece exhaust was also integrated
innovatively in the overall packaging at the rear.
Audi also uses the fin as a design element. “I think that we found a good
compromise by attempting to view the fin as an active element,” says Dr. Wolfgang
Ullrich who is proud of the new Audi R18 TDI prototype’s aerodynamic efficiency.
“Aerodynamics has always been one of Audi’s core skills. It speaks for itself that in
spite of significantly reduced engine power we reach almost the same top speed and
levels of downforce like last year with the R15 TDI.”

Audi Communications Sport.

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