Aerodynamic investigation of a vehicle in highly turbulent flow

Abstract

This master’s thesis presents the design, simulation, and experimental validation of an active turbulence generator aimed at reproducing realistic, highly turbulent flow conditions for vehicle aerodynamic testing in a scale wind tunnel. The main goal is to bridge the gap between idealized wind tunnel tests and the unsteady, turbulent flow scenarios encountered during real-world highway and urban driving. To achieve this, an active turbulence generator using oscillating airfoils was developed. The airfoils, based on the NACA 0015 profile, were actuated to produce adjustable turbulence intensities and length scales, matching conditions such as turbulence intensities of 1–5% for highway speeds in real-world driving scenarios. Computational Fluid Dynamics (CFD) simulations were conducted using the κ−ω SST turbulence model with an overset mesh technique to accurately resolve the unsteady interaction between the moving airfoils and the freestream. The simulations analyzed characteristic parameters including turbulence intensity, turbulent length scale distributions, and aerodynamic loads on a DrivAer reference model. The design was optimized to ensure turbulence generation across the test section while keeping the required mechanical power within feasible limits. A mechanical system driven via a single motor through a chain was designed and manufactured using rapid prototyping techniques, allowing synchronized oscillatory motion of all seven airfoils. The system was integrated into the Chalmers scale wind tunnel and tested. The findings serve as a solid foundation to be built upon in future projects regarding the development of an active turbulence generator.