SAE International

uses bramble

SAE International

SAE International or the Society of Automotive Engineers is a US based professional association for engineering professionals. Publishing vital research articles for mobility engineers. Below are the findings from a white paper in which bramble CFD was used.

The Challenge

To research tyre deformation and its effect on open-wheel race car aerodynamics at high velocities. Particularly measuring acceleration at a corner exit, something that is difficult to measure in a wind tunnel.

Analysing aerodynamic performance is key in general purpose cars to reduce fuel consumption and improve energy efficiency. However in race cars, aerodynamics is used to improve the downward force of the car, thus increasing its ability for acceleration, braking and cornering.
The vehicle’s wheels pay a huge part in this and various research has been done on it. Most recently studies have focused on tyre deformation, however when studying acceleration at a corner exit this is hard to measure accurately in a wind tunnel.

The bramble solution

Using a full-vehicle steady-state CFD model of Formula 3 car (Dallara F317), three maneuvers characteristic of race cars were simulated. A straight-line braking (SLB), end of straight driving (EOSD), and high-speed cornering (HSC) manoeuvre. The tyre deformation included proper wheel load, car speed, wheel speed, camber angle, and slip angle for each wheel.

The CFD full-vehicle model took chassis slip angle, body roll angle, and wheel steering angle into account in order to match the real driving situation.

The geometry of the car was changed as the tyres were deformed, ensuring that the chassis was kept at the same ride height, pitch angle and roll angle.

The dimensions of the simulated wind tunnel was 50m in front of the car, 100m behind the car, 25m each side and 26m above.

Meshing – the car model included 95million hexahedral, 1.5 million prism, and 13 million polyhedral cells. The high use of hexahedral cells against polyhedral cells speeds up the meshing time. A kinematic model was included reproducing pitch, yaw, and roll movements as well as kinematic effects like camber changes, toe changes etc. Plus four regions of rotating reference frames have been added to each of the four wheels.

Reprinted with permission from Figure 17 of “Tire Deformation Modelling for High-Speed Open-Wheel Aerodynamic Investigations”, SAE Int. J. Veh. Dyn., Stab., and NVH 5(3): 233 – 248, 2021, doi: 10.4271/10-05-03-0016. © SAE International

Reprinted with permission from Figure 25 of “Tire Deformation Modelling for High-Speed Open-Wheel Aerodynamic Investigations”, SAE Int. J. Veh. Dyn., Stab., and NVH 5(3): 233 – 248, 2021, doi: 10.4271/10-05-03-0016. © SAE International

Value Realised

The results showed that the tire deformation of the vehicle had an effect on the car aerodynamics of up to a 2.5% for the 3 different manoeuvres, which in turn affected the lap time by 0.22 seconds.

“The relative change of the L/D between undeformed and simulated deformed tyres is about 2.4% during straight-line driving and about 2.5% during SLB. The aerodynamic balance during the SLB shows a relative change of 2.3% for this comparison. The increased temperature of the simulated tyres leads to a relative change of 2.5% in downforce and 1.2% in aerodynamic balance to the front during HSC, which might be felt while driving. In comparison to that, the same effect in aerodynamic balance can be achieved by a change of 1-2° in the angle of attack of the front wing flap. The influence on the lap time of the aerodynamic findings reported in this article is 0.22 s.”

Eder, P., Amhofer, T., Gerstorfer, T., and Lex, C., “Tire Deformation Modelling for High-Speed Open-Wheel Aerodynamic Investigations,” SAE Int. J. Veh. Dyn., Stab., and NVH 5(3):233-248, 2021, doi: 10.4271/10-05-03-0016. © SAE International

“In general, it can be concluded that the area behind the tyres is the flow region that is most affected by the tyre deformation.”

SAE International