Investigation on aerodynamic force behavior and flow structure of Ahmed body under crosswind

Abstract

This study investigates the aerodynamic performance and the near wake of the Ahmed body under crosswind conditions experimentally at a length-based Reynolds number ${\mathrm{Re}}_l$ $\in$[0.11, 0.64] × 10⁶. The slant angle of the Ahmed body is 35°, and the yaw angle (β) ranges from 0° to 30°. Throughout the investigations, force, pressure, particle image velocimetry (PIV) and flow visualization measurements are conducted. The variation of drag coefficient $C_d$ with yaw angle follows a parabolic curve, with a remarkable increase in $C_d$ occurring at 6°<β < 16° yaw angle. Non-uniformity and asymmetry in pressure distribution are shown on the base and slant surfaces, which can be attributed to the asymmetry behavior of recirculation structures behind the body. As the yaw angle increases, the shrinking of recirculation structures and the movement of their foci toward the surface contribute to a significant reduction in pressure on the leeward side of rear surface, thereby increasing drag. The shear layer on the windward side is suppressed, while on the leeward side, it separates prematurely, corresponding to an increase in the side force. Based on the findings of the present study and previous literature, a conceptual model of the flow structure is proposed for the 35° slant angle Ahmed body under crosswind, aiming to explain the evolution of the behavior of forces, pressure distribution, and the flow structures.