The Impact of Non-Linear Aerodynamics on Racecar Behaviour and Lap Time Simulation 2002-01-3332
Despite massive research efforts carried out by racing car manufacturers aerodynamics is probably the most unexplored field in the design of high performance vehicles. Scale wind tunnel testing is still the most effective way for the development of a new car, CFD codes being at the experimental stage.
Wind tunnel engineers produce what is called an “aero map”: a simple graph expressing aerodynamic forces versus ride height. That means, drag, downforce, and relative distribution are measured on an array of front and rear different ride heights.
The same concept can be applied to track testing with the use of proper sensors on the real vehicle, such as ground height laser sensors and suspension force transducers.
Reading such a map and relating it to static and dynamic suspension characteristics is a vital task for performance optimisation. In the perfect world the centre of pressure would always be in the ideal position anywhere on the track, thus enabling the driver to make the most out of the car.
As a matter of fact any unwanted, back and forth movement of the centre of pressure due to pitch and/or heave (e.g. under power, in braking, or on road bumps) affects cornering behaviour: the car can be perceived as difficult and tricky for the driver thus jeopardising performance.
A module dedicated to non-linear aerodynamics (called “Aerolap”) has been added to the RCS software for lap time simulation, working in close co-operation with the Minardi Formula 1 and BMS Scuderia Italia teams. The vehicle model can now take into account the effects of ride height variations on aerodynamic forces, as well as non-linear suspension and tire ground stiffness. The user can therefore simulate the impact of set-up modifications on aerodynamic balance along the track as well as on overall performance.
The RCS project (presented at the 2000 SAE Motorsports Engineering Conference in Detroit) was conceived as a pit lane support tool for the race engineer, who usually works under pressure in a noisy, stressing environment were things happen -and decisions are taken- all very quickly. Therefore a particular effort was devoted to interface and graphics. Regarding the Aerolap an innovative method was devised for map visualisation as an alternative to the usual contour plot. This seems to enable a far more intuitive correlation with performance results.
On the math side two different methods were used to approximate the aero map surface: a Gaussian array and the so-called Akima's triangles, the former giving more reliable results where extrapolation is required.