On the ground-vehicle induced flows and obstacle interaction for energy harvesting purposes

CFD simulations were conducted with the aim of studying the flow field induced by a road vehicle moving at high speed for energy harvesting purposes. 2D and 3D approaches were used and focus was put on the interaction between the vehicle and an obstacle placed upon the road simulating the shape of a generic harvesting device. 2D RANS simulations have proved that a separated region forms and that a trailed flow exists upon the vehicle which thickness do not exceed 1.1 times the vehicle height. The presence of trailing vehicles was analyzed and the raising of the separation region evaluated. The 3D steady approach showed that 2D modeling did not adequately predict velocity and pressure values even if general trends were captured. Different panel shapes were then compared to assess the effect of placing an obstacle near the moving vehicle. 2D URANS simulations suggested that to overcome an obstacle placed 1 m above the vehicle roof, an energy boost is required, while 3D unsteady calculations showed negligible variations in the vehicle's drag with approaching the obstacle. Furthermore, simulation of the full 3D domain allowed to identify forces time-histories and loading directions acting on a circular cylinder, with definition of an equivalent uniform velocity to characterize the flow impinging on the obstacle. Results showed that force coefficients and equivalent velocity maximums locate in the vehicle nose region, where inviscid-like effects dominates.