At IIT (Illinois Institute of Technology) Motorsports, we had a challenge. Our student team of 30-plus motivated engineers wanted our Formula car to go fast, but we also needed to create a great amount of downforce so that the car sticks to the racetrack and can perform high-speed turns. The problem is that increasing the downforce increases the drag. The solution is to fit the car with a drag reduction system (DRS) in the style of Formula One cars, in which parts of the rear wing (the second and third elements, in our design) will be rotated about their quarter chord point to an angle of attack at which they generate less downforce. This reduces drag when the car is moving in a straight line while allowing activated by control systems based on driver action rather than direct driver inputs. The CFD simulation images depict the ON and OFF settings for the system.
Rear wing ADRS OFF: The wings create an increased downforce that allow the driver to perform high-speed turns safely.
Rear wing ADRS ON: The wing positions create minimum drag and allow the driver to go as fast as possible.
Creating the System
It is impossible to test different wing configurations and design on the racing circuit. Simulation is needed to design this ADRS. We used ANSYS computational fluid dynamics (CFD) for the simulations. CFD allows us not only to look at the flow and pressure pattern on the wing, but also accurately compute the downforce and drag of the different configurations. For example, in a design where the ADR is not engaged, we are able to get 780 N of downforce, but this came with 221 N of drag. When we engage the DRS, the drag of the wing drops by 85 percent to 37 N (the downforce drops to 148 N, but downforce is not important when the ADRS is engaged).
Additional Use of Simulation for Aerodynamic Design
We use CFD simulation for other aerodynamic design elements, including the front of the car (shown below).
Additionally, to reduce trailing edge vortices, we simulated a configuration of the wing with gills on the upper part of the endplate. We included gills to allow some high-pressure air from the top surface of the wing elements to escape. While this likely reduces downforce because of a reduced pressure differential, it can also reduce drag even more because of reduced vorticity. See an example below.
Skin friction and air flow over the front wing and car body
Gills allow some high-pressure air from the top surface of the wing elements to escape, resulting in reduced drag.
We are currently competing in our 10th consecutive year of Formula SAE competition, and have just returned from our second trip to the Formula Hybrid Competition, in Loudon, New Hampshire. Continuing our streak, we placed in the top five in the electric car category.
If you want to know more about our team, please visit our website. At IIT Motorsports, we strive to create long-lasting partnerships that offer knowledge and are mutually beneficial. All kinds of support are welcome. More information at http://fsae.iit.edu/sponsor/index.html.
Note from ANSYS: Did you know that ANSYS provides FREE engineering simulation software for university- based student teams participating in competitions such as Formula, Baja and Aero Design SAE, plus the American Solar Challenge and many more? Click here for more information.