Drag Reduction in Ground Vehicles using a Model Porous Medium

Abstract

This research investigates aerodynamic drag reduction on a 25° Slanted Ahmed Body (SAB) by integrating porous media model rods through combined experimental and computational methods at a Reynolds number of 1.16×10⁴. Two porous media configurations: short rods (6.75% of the model height) and long rods (20.0% of the model height), both featuring cylindrical rods with 80% porosity, were systematically compared against a baseline SAB. In-depth analyses were performed to investigate the wake flow topology, recirculation region characteristics, pressure coefficient distribution, Reynolds stress distributions and drag coefficient. Experimental investigations employed particle image velocimetry for precise flow visualization, while Reynold Averaged Navier-Stokes numerical simulations through a COMSOL Multiphysics software were used to complement and extend the experimental insights. Key findings revealed that incorporating porous rods significantly enhanced wake filling, marked by accelerated recovery of streamwise momentum and reduced wake momentum deficits. This wake filling effect contributed directly to an increased base pressure and notable reduction in pressure drag. Moreover, the porous model rods effectively modified Reynolds stress distributions, resulting in more stabilized, coherent wake structures with increased recirculation length and stability. Quantitatively, the long rod configuration yielded the most substantial aerodynamic improvement, achieving an 8.27% drag reduction compared to the baseline SAB, while the short rod configuration demonstrated a modest but meaningful reduction of approximately 3%. These comprehensive analyses confirm the efficacy of a porous medium as an innovative passive drag-reduction strategy in automotive applications, emphasizing their potential to optimize vehicle aerodynamic performance through targeted wake stabilization and pressure recovery enhancements