Wake Dynamics of Heavy Road Vehicles: Characterization and Control with Rear Flaps*

In the context of climate change, heavy road vehicles are a major contributor to global pollution. Therefore aerodynamic devices are paramount in reducing their drag and improving their energy efficiency. The main source of drag comes from pressure drag due to the flow separating at the rear part of the vehicle. A successful solution to control the flow is installing flaps on the top and the sides of the rear of the vehicle. Here we present a state-of-the-art experiment on the wake dynamics of a realistic scaled model of a truck in a wind tunnel, with a rolling road to simulate the ground effect. The experiment is carried out at different yaw angles. For each case, a parametric study to determine the optimal shape and angle configuration of the side and top flaps is carried out. A time-resolved three-dimensional particle tracking method (Shake-the-Box) and planar particle image velocimetry (PIV) are used to reconstruct the development of the wake. Additionally, the pressure at the rear of the truck is measured to enhance the understanding of wake dynamics and a load cell is used to measure the forces and moments exerted on the vehicle. Our setup enables for the first time an accurate spatio-temporal measurement of the coherent structures linked to the generation of drag. The results give an optimised flap configuration to reduce drag, offering valuable insights for practical applications in the heavy road vehicle industry.