Effects of Reynolds Number On the Wake Characteristics of a Notchback Ahmed Body

Abstract

This paper investigates the effects of Reynolds number on the wake characteristics of a notchback Ahmed body with effective backlight angle, βe = 17.8°. The Reynolds number based on the body height was varied from 5 × 103 to 5 × 104. Prior to the Reynolds number investigation, a Reynolds-Averaged Navier-Stokes (RANS) model assessment was performed using nine turbulence models consisting of one- and two-equation eddy-viscosity models and second moment closure models. The standard Spalart-Allmaras model was the only model that accurately predicted the asymmetric time-averaged wake topology, as reported in previous studies, for the βe = 17.8° notchback Ahmed body at Re = 5 × 104. The drag coefficient decreased with increasing Reynolds number, while the lift coefficient remained constant for Re = 1 × 104. The wake structure exhibited three regimes: symmetric (Re = 1 × 104), transitionally asymmetric (1 × 104< Re = 3.5 × 104) and fully asymmetric (Re ≤ 3.5 × 104) states. The wake asymmetry was attributed to an imbalance in entrainment from the side and asymmetric separation from the roof and the C-pillars of the body. The tilting and stretching terms in the vorticity transport equation were used to provide insight into the source of asymmetry in the vorticity field around the body.