Investigations of the Rear-End Flow Structures on a Sedan Car

Abstract

The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. AbstractThe aerodynamic drag, fuel consumption and hence CO 2 emissions, of a road vehicle depend strongly on its flow structures and the pressure drag generated. The rear end flow which is an area of complex three-dimensional flow structures, contributes to the wake development and the overall aerodynamic performance of the vehicle.This paper seeks to provide improved insight into this flow region to better inform future drag reduction strategies. Using experimental and numerical techniques, two vehicle shapes have been studied; a 30% scale model of a Volvo S60 representing a 2003MY vehicle and a full scale 2010MY S60.First the surface topology of the rear end (rear window and trunk deck) of both configurations is analysed, using paint to visualise the skin friction pattern. By means of critical points, the pattern is characterized and changes are identified studying the location and type of the occurring singularities. The flow field away from the surface is then analysed using PIV measurements and CFD for the scale model and CFD simulations for the full scale vehicle. The flow field is investigated regarding its singular points in cross-planes and the correlation between the patterns for the two geometries is analysed.Furthermore, it is discussed how the occurring structures can be described in more generalized terms to be able to compare different vehicle geometries regarding their flow field properties.The results show the extent to which detailed flow structures on similar but distinct vehicles are comparable; as well as providing insight into the complex 3D wake flow.

Importance of Sub-Grid Scale Modeling for Accurate Aerodynamic Simulations

“…Several studies have also shown this to be true for more realistic fastback and notchback geometries, see, e.g., Refs. [13][14][15][16]. All these findings show the importance of capturing these vortices and wake structures accurately.…”

An Aerodynamic Assessment of Vehicle-Side Wall Interaction using Numerical Simulations

“…However, this evaluation was carried out by neglecting the presence of the side wall. The side wall was disregarded for this study so that we could assess both the accuracy of turbulence models and the grid chosen by comparing the reported drag coefficient ( ) on the vehicle from the literature [20] which is very much in agreement with experimentally reported values of Kounenis et al [21] for a Volvo S60 vehicle and Heft et al [22] for DrivAer Fastback models which suitably represent both the vehicle topology [23] and Reynolds numbers investigated in the present work. The definitions of the aerodynamic force coefficients used in the present study namely, the drag force coefficient ( ), the lift force coefficient ( ) and the side force coefficient ( ) are summarised as follows:…”