The influence of Reynolds number on the unsteady turbulent wake regimes of a notchback Ahmed body

• Notchback Ahmed body β e = 17.8 ° exhibits both symmetric and asymmetric wake regimes. • At R e h = 1 × 10 4 , the wake is symmetric with synchronized vortex shedding from the body sides. • Low Reynolds number enhances viscous effects, producing near-wall reverse flow. • At R e h = 5 × 10 4 , the wake transition to a fully asymmetric state with bimodal switching. • Wake asymmetry arises from imbalanced shear-layer separation and entrainment. This study investigates the influence of Reynolds number on the unsteady turbulent wake regimes of a notchback Ahmed body with an effective backlight angle of 17.8°. Three-dimensional improved delayed detached eddy simulations (IDDES) were conducted at two Reynolds numbers, Re h = 1 × 10 4 (denoted as Re1E4) and Re h = 5 × 10 4 (Re5E4), representing symmetric and fully asymmetric flow regimes, respectively. Detailed aspects of the wake dynamics, including the mean flow, Reynolds stresses, vortex shedding, global instabilities, and the pumping motion (i.e., quasi-periodic expansion and contraction) of reverse flow regions, are used to characterize the effects of Reynolds number. At Re1E4, the results showed a symmetric wake with a near-wall reverse flow region downstream of the body. In contrast, the wake of Re5E4 is characterized by asymmetric reattachment on the deck and a directional bias of the vortical structures towards one side of the body. This asymmetry is induced by uneven separation along the sides of the slant, which enhances the C-pillar vortex and downwash flow on one side. As a result, the turbulence statistics, turbulence production, vortex shedding, and pumping motion in the reverse flow regions are enhanced on the opposite side of the body. Furthermore, the unsteady wake of Re5E4 exhibited bimodality with a long characteristic switching timescale.