The nature of the vortical structures in the near wake of the Ahmed body

James Venning (1) , David Lo Jacono (2) , David Burton (3) , Mark C. Thompson (1) , John Sheridan (1)

1 Fluids Laboratory for Aeronautical and Industrial Research - FLAIR (Victoria, Australia)
2 IMFT - Institut de mécanique des fluides de Toulouse
3 Department of Mechanical and Aerospace Engineering [Victoria]]

This study presents the results from high-spatial-resolution water-channel velocity-field measurements behind an Ahmed body with 25° rear slant angle. The Ahmed body represents a simplified generic model of a hatchback automobile that has been widely used to study near-wake flow dynamics. The results help clarify the unresolved question of whether the time-mean near-wake flow structure is topologically equivalent to a toroidal vortex or better described by a pair of horizontally aligned horseshoe vortices, with their legs pointing downstream. The velocimetry data presented allows the tracking of the vortical structures throughout the near wake through a set of orthogonal planes, as well as the measurement of their circulation. The spanwise vortices that form as the flow separates from the top and bottom rear edges are shown to tilt downstream at the sides of the body, while no evidence is found of a time-mean attached toroidal vortex, at least for the Reynolds number (based on the square root of the frontal area) of Re~30000 under consideration.

Mots clés: Ahmed body; PIV; Vortices

Domaines: Mécanique des fluides [physics.class-ph]

James Venning, David Lo Jacono, David Burton, Mark C. Thompson, John Sheridan. The nature of the vortical structures in the near wake of the Ahmed body. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 2017, vol. 231 (n° 9), pp. 1239-1244. ⟨10.1177/0954407017690683⟩. ⟨hal-01613104⟩