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Computational Fluid Dynamics (CFD) simulations have the potential to provide highly-resolved representations of the complete flow field around a vehicle. However, this comes at a cost: even with substantial computing resources it is not practical to match the throughput of conventional wind-tunnels. One way of redressing this is to extract the maximum value from each simulation. This paper explores a structured approach to this task, illustrating it with examples from Jaguar Land Rover programmes. It shows, through the example of the Jaguar XF programme that a combination of simulation and relatively simple full-scale wind-tunnel testing, can deliver competitive aerodynamic performance.

This paper presents a series of observations of time-averaged wake asymmetry for a range of “notchback” vehicle geometries. The primary focus is on a reduced scale experiment using full-sized saloon geometry. Substantial flow asymmetry was observed in the vehicle “notch”. Similar asymmetries are reported for a full scale experiment on the same geometry along with others as diverse as production models of a luxury and mid-sized saloon; basic car shapes and a simple body. In one case a physical explanation is proposed, based on the degeneration of an unstable symmetric wake structure.

Simulation of local flow structures in the A-pillar/side glass region of bluff SUV geometries, typical of Land Rover vehicles, presents a considerable challenge. Features such as relatively tight A-pillar radii and upright windscreens produce flows that are difficult to simulate. However, the usefulness of aerodynamics simulations in the early assessment of wind noise depends particularly on the local accuracy obtained in this region. This paper extends work previously published by the author(1) with additional data and analysis. An extended review of the relevant published literature is also provided. Then the degree to which a commercial Lattice-Boltzman solver (Exa PowerFLOW™) is currently able to capture both the local flow structure and surface pressure distribution (both time averaged and unsteady) is evaluated. Influential factors in the simulation are shown to be spatial resolution, turbulence and boundary layer modelling.

MIRA and Rover Group Ltd have undertaken a systematic study of the ability of CFD methods to predict the aerodynamic characteristics of simplified car-like shapes. This paper reports the latest stage of this investigation, which examines the use of a commercial Reynolds-averaged Navier-Stokes code (STAR-CD) to predict the aerodynamic characteristics of a series of simplified car shapes. Comparable experimental data were obtained by testing in the MIRA Full Scale Wind Tunnel (FSWT). This paper shows that CFD techniques are improving in their ability to predict flow separation from curved surfaces accurately. Further, encouraging results for vehicle drag (coefficients to within 2% of experiment) and the effect of limited geometric modifications on drag (within 7% of full-scale experiment) were obtained. However these latter results should be viewed with some caution as the results for lift were considerably poorer.