A research into the flow and vortex structures around vehicles during overtaking maneuver with lift force included

Abstract

A simulation model of overtaking maneuvers is established to research into the flow and vortex structures around two identical Ahmed vehicles. The simulation demonstrates how the flow and vortex structures generate and change, which influences the aerodynamical coefficients of the vehicles most. In this study, a transient solver is used on the platform of ANSYS/Fluent, and the sliding mesh method is adopted to simulate the motion of the overtaking vehicle, which realizes a more actual recovery of the road conditions. Based on the fact that the primary factor that influences the aerodynamical coefficients of a vehicle is the change in the outer flow around it, a research into the variation in the outer flow field is conducive to in-depth analysis of the aerodynamical characteristics of the vehicle. Most previous studies focused only on the lateral aerodynamical coefficients during overtaking maneuvers. This article establishes a comprehensive model that takes the lift force into consideration to more accurately simulate the aerodynamical characteristics. Moreover, it is aimed at figuring out the key factors that cause the change in the aerodynamical coefficients at vortex level in this study, not just at pressure level as most previous studies did.

Influence of Small Vehicle on Transiting Test Method for Measuring Building Wind Pressure Coefficients

“…The wind pressure coefficient of the model is unaffected by the overtaking behavior. By combining the pressure contour and the isosurface of velocity in Shao et al [27], the two vehicles do not interfere with each other when their lateral distance is far enough. For the experiments in this section, the two vehicles are separated by one lane, and their lateral spacing is significantly large.…”

“…Howell et al [26] found that a small lateral distance increases the peak value of each aerodynamic parameter. In addition, different relative velocities also have varying effects on the flow field around two vehicles [27]. Furthermore, the relative velocity does not affect the trends of the aerodynamic coefficient curves of two vehicles, but it can affect their peak value [28].…”

“…Uystepruyst and Krajnović [29] numerically simulated the overtaking process using the Ahmed model with different relative velocities during overtaking; they obtained various influences on the aerodynamics of the overtaken vehicle. In addition to the overtaking behavior, the wake formed by the traveling vehicle could affect the flow field over a long distance behind and affect the vehicle behind [27,30]. The change curve of the aerodynamic coefficient with longitudinal distance during the overtaking process in Noger et al [31] demonstrated that the vehicle in front could also affect the aerodynamic coefficient of the vehicle in the rear within a certain distance after overtaking.…”

Numerical and experimental study of two-vehicle overtaking process

“…The overtaking process has been extensively studied using numerical modeling. Clarke and Filippone, 12 Uystepruyst and Krajnovic, 13 and Shao et al 14 simulated the overtaking process for two car models to determine the effect of lateral separation and relative speed for two models on the aerodynamic forces that act on them. The results show that there is increased interference between the aerodynamic forces that act on the vehicle models as the lateral separation decreases and/or the relative velocity between the two vehicle models increases during the overtaking process.…”

“…In terms of the computational resource that is required for a simulation, most numerical studies of the overtaking process use two-equation Reynolds-averaged Navier-Stokes equation (RANS) models, which are, to a certain degree, reliable and economic turbulence models. These include the standard k − ε model, 12 the RNG k − ε model, 12,16 the realizable k − ε model, 14 the SST k − ω model, 12,20–22 the ζ − f model 13 and the low-Reynolds-number k − ε model. 20 The SST k − ω model 12,20,22 gives an accurate prediction of the aerodynamic characteristics among these RANS models because it predicts near-wall flow behavior if there is an appropriate design for the near-wall grid mesh.…”