Validation of CFD Aerodynamics Simulations of the Cadillac Celestiq with Comparison to Wind Tunnel Data

In the context of vehicle electrification, improving vehicle aerodynamics is not only critical for efficiency and range, but also for driving experience. In order to balance the necessary trade-offs between drag and downforce without significant impact on the vehicle styling, we see an increasing amount of active aerodynamic solutions on high-end passenger vehicles. Active rear spoilers are one of the most common active aerodynamic features. They deploy at high vehicle speed when additional downforce is required. For a vehicle with an active rear spoiler, the aerodynamic performance is typically predicted through simulations or physical testing at different static spoiler positions. These positions range from fully stowed to fully deployed. However, this approach does not provide any information regarding the transient effects during the deployment of the rear spoiler, which can be critical to understanding key performance aspects of the system. In this paper, we propose a methodology leveraging Computational Fluid Dynamics (CFD) simulations utilizing the Lattice Boltzmann Method (LBM) enabling the accurate simulation of transient aerodynamics forces during deployment of a rear spoiler on a production level passenger vehicle. The simulation results are then compared with full-scale wind tunnel physical test data as a validation of the approach. This capability enables engineering teams to provide information to guide design decisions and can be generalized to model other types of active systems on cars such as active grilles and front splitters.