On low-frequency pressure fluctuations and their impact on vehicle aerodynamics in a full-scale automotive wind tunnel

Low-frequency pressure fluctuations pose significant challenges in the design and operation of full-scale automotive wind tunnels. However, the mutual interactions between wind tunnel pressure fluctuations and test vehicle aerodynamics remain unclear. This study employs high-fidelity numerical simulations to investigate the characteristics of low-frequency pressure fluctuations and their influence on vehicle aerodynamics. A virtual wind tunnel was constructed to replicate the geometry of a real-world facility, and Detached Eddy Simulations were utilized to capture the low-frequency pressure dynamics within the test section. Simulations were performed for three configurations: (a) an empty test section, (b) a vehicle mounted test section, and (c) an open-road setup. Reduced order analyses were applied to compare the spatiotemporal characteristics of the pressure and velocity fields across all configurations. The simulation results show that pressure fluctuations have a minor influence on the time-averaged drag coefficient, despite a noticeable enhancement in the temporal variation of the low-frequency drag. A global standing-wave pattern that governs the pressure field in the pulsating wind tunnel is revealed by reduced-order analyses, where the characteristic frequency is found to decrease due to the installation of the test vehicle. In addition, a significant coupling effect is observed between the coherent structures in the wind tunnel shear layer and the vehicle wake, elucidating the complex aerodynamic interactions between the wind tunnel and the test vehicle that are inherent to automotive wind tunnels. These results provide useful insights to guide the optimization of wind tunnel design and real-world experimental execution, which will ultimately enhance the precision and reliability of aerodynamic evaluations in real-world automotive wind tunnels.