CFD Simulations Ecurie Aix

Every year we, as the Formula Student Team of RWTH Aachen University, develop a completely new electric race car and revise a previous car to be able to drive autonomously. For our Aerodynamics team, the electric vehicle is the main focus. We try to find the best geometries for our car within the regulatory constraints and while keeping performance compromises with other design areas in mind. To help us design and improve our aerodynamic package, we carry out extensive CFD simulations, using Siemens Star-CCM+.

Methods: 
Over the years, our simulations have been developed further and further to improve accuracy, resulting in several simulation approaches being used currently, depending on the desired information about the different aerodynamic phenomena and influences on the racetrack. These include a straight-line half car simulation using a symmetry plane which consists of around 50 million cells, a full car simulation with a yawed car and turned front tires as well as a cornering simulation, the latter two both using around 90 million cells. In our development process, we mainly use the straight-line and yaw-angle simulations as they provide much quicker turnaround times and yield enough information. The yawed car is used to include the influence of various driving states on our aerodynamic performance. This is especially important because the purpose of our high-downforce vehicle concept is to increase performance in grip-limited driving conditions, which means those are also the situations in which the car state differs most from the neutral state. This is also the reason for the development of the cornering simulation. Here, the car can be fully transformed to represent real driving situations in corners, including a curved wind tunnel which makes sure that the air flow relative to the vehicle matches the real air flow during cornering. For these simulations we are switching from the k-epsilon turbulence model

Apart from the external aerodynamics, we also use CFD simulations for the design of our cooling systems. These include a water-cooling circuit for our four electric motors and the corresponding inverters as well as an air-cooled battery. Apart from system simulation in MATLAB Simulink and Siemens Amesim, we use thermal CFD simulations to analyze their behaviour.

Results:
Over the course of 2021, we put a lot of effort in developing a completely new aerodynamic package including the development of a new front wing, undertray, rear wing, tire wake components of smaller size and a new cooling package. The next upcoming new car will be able to compete in both autonomous and electric disciplines. With the merge of our driverless (autonomous) car and our electric car and other major geometry changes like a new monocoque and a new wheel package we saw the need of developing a new aerodynamic package as well.
Our aerodynamic package is currently in a state where it is performing better than our predescessing concept despite still having key areas to improve on in this current state. We are aiming to increase our downforce in comparison to our previous car by 20% until the end of this season.

In terms of cooling we were able to increase the heat flux in our cooling sleeves for our four distinctive motors by over 100% while maintaining the same pressure drop. Also, we are currently developing our own microtube radiators. This type of radiator enables a much higher heat dissipation, taking advantage of the principle of the Carman’s vortex street. Our estimations done in a MATLAB model show a potentially higher heat dissipation of over 25% with a 60% reduction in weight and size. This is also enhanced by the new design of our inverter cooling plate which also reduced it’s weight by 10% and it's pressure drop by 60%.

Furthermore, after an elongated period of development in home office compromised by the pandemic we were able to finalize and manufacture the past concept of our racing car, the “eace09”. This past summer of 2021 where the races/events take part, has brought us to the best results as a team so far.
We were able to collect a lot of trophies, particularly an “Overall 1st” win on the RedBull Ring in Austria. 

This past season, having been the most successful season in our club’s history was substantially supported by the possibility of using the high-performance computing capabilities of the RWTH Compute Cluster for the development of our aerodynamics.

Summary:
The team Ecurie Aix participates in the Formula Student, the biggest international development competition of its kind, for which a new race car is build every year. Formula Student does not only generate immense attraction for industrial partners, but also for scientific institutions, since the research often overlaps and yields scientific theses and future employees. 
The development of a race car does not simply contain of craftsmanship in the workshop. It requires an intense conceptualization, for example the development of the car’s aerodynamic parts in thousands of CFD simulations. 
Since these complex simulations cannot be performed by the student’s notebooks, Ecurie Aix was granted to use the high-performance computing possibilities of the RWTH Compute Cluster for the development of the aerodynamic package.