Flow Structure Investigation of a Truck under Crosswinds

Abstract

This paper investigates the flow structures on the near- and far-wake of a 1/8th scaled simplified heavy vehicle model called Ground Transportation System (GTS) model using a steady-state Reynolds-averaged Navier-Stokes (RANS) with k-ω Shear Stress Transport (SST) turbulence model at Reynolds number (Re) of 1.6 × 106 and yaw angles (Ψ) = 0o-14o. The current CFD results have been validated using experimental data from the literature. Two crosswind conditions based on the crosswind incidence angle (β) are adopted; β < 90o is called crosswind, and β = 90o (perpendicular to the GTS side surface) is called pure crosswind. Vortex detection scheme based on Ω method and total pressure coefficient (Cpt) contours is used to visualize the wake structure. With Ψ, vortices on the GTS roof take birth as a result of pressure differences between the windward and leeward sides. These vortices grow in size as they travel downstream. The growth in size is related to the Helmholtz theorem of vorticity and Kelvin’s Circulation Theorem. The vortices merged at Z/W > -4 (Z/W = 0 is the GTS rear surface) downstream of the GTS for Ψ = 7.5o and 14o. The merged vortex dissipates at Z/W > -6 and Z/W > -8 for Ψ = 7.5o and 14o, respectively. In the pure crosswind condition, the merged vortex attaches to the ground due to the velocity difference between the freestream and the moving computational ground used in the present simulation. At Ψ = 14o, surface streamlines on the GTS surface show the creation of two co-rotating vortices on the windward roof. For the present Ψ, similar flow structures between the two crosswind conditions are shown. Initial results show that the aerodynamic crosswind stability of a truck is related to the spanwise pressure difference between the windward and leeward surfaces of the truck.