Flow around a circular cylinder inside a hybrid channel

Abstract

Motivated by the substantial contribution of the wheel region to ground-vehicle aerodynamic drag, the present study examines flow around a circular cylinder inside a straight-curved hybrid channel as a reduced-order representation of the coupled wheel-ground-housing system. Large-eddy simulations are employed to quantify the aerodynamic forces and Reynolds-number-dependent evolution of the associated flow structures. The Reynolds number based on the cylinder diameter spans ReD = 3.6 × 103 to 3.6 × 106, and that based on the half-channel height covers Reδ = 4.0 × 102 to 4.0 × 105. The results show that increasing ReD significantly reduces the mean drag coefficient C¯D from 8.0 to 1.1 while increasing the mean lift coefficient C¯L from 3.9 to 5.9. The root mean square drag and lift coefficients rise rapidly from a regime in which the separated shear layers remain relatively stable, and wake fluctuations are of limited amplitude, attaining a maximum at ReD = 3.6 × 104. Combined examination of the surface pressure gradient and wall shear stress identifies flow separation occurring near 277°–287°, with its extent strongly influenced by both Reynolds number and curvature-induced acceleration. Upstream of the curved section, the velocity-deficit profiles depart from the canonical parabolic form, with stronger near-wall deficits at lower Reδ. Downstream of the cylinder, the peak streamwise velocity fluctuation moves progressively toward the cylinder as Reδ increases, while its magnitude first increases and then decreases, consistent with the trends of force fluctuations. These results demonstrate that the aerodynamic loading, separation behavior, and wake dynamics are controlled by the coupled action of non-uniform confinement, wall curvature, and streamwise flow acceleration.