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The aerodynamic development and evaluation of passenger vehicles is almost universally performed in the controlled, low turbulence environment of a wind tunnel or under similarly idealized conditions using CFD. This environment is substantially different from that which is experienced on-road due to the effects of atmospheric winds and the wake flows from other road vehicles. The scope of this work is to establish, with regard to surface pressures, if a low turbulence wind tunnel evaluation of passenger cars yields results which accurately reproduce on-road data or whether a more complete simulation of the real world is required. The test vehicle was a Rover 214, a typical European mid-sized hatchback. Data were obtained from both the MIRA full-scale wind tunnel and on the road using the same vehicle and instrumentation. The on-road data were gathered under various atmospheric wind conditions.

Road vehicle models are tested in a wind tunnel with a moving ground when an accurate simulation of the under-floor flow is required, for instance for the aerodynamic development of the underbody. The use of a moving ground necessitates that the model and wheels be supported using one or more struts. These struts can cause complex interference flow fields including three-dimensional separations in the area surrounding them. This work aims to quantify the magnitude of these interference effects for a saloon vehicle and to begin to explain the physics of the flow. Models were mounted over a stationary ground plane using an under-floor balance to measure aerodynamic forces and moments on the model. Each model is tested with and without mock struts, which do not actually support the model. Comparisons are made between results from configurations with and without the mock struts in order to quantify their aerodynamic effects.

Transient wake surveys have been conducted on a generic three dimensional vehicle shape. The flow conditions were those generated by the unique crosswind facility at Durham University, which imitates a vehicle passing through a sharp-edged, finite length cross-wind gust. Each survey consisted of some 7000 cross-wind gusts, with each point in the wake being phase-averaged over 20 gusts. The surveys clearly show the development of the wake structure from the familiar axial flow conditions, through the transient to a nominally steady yawed flow. Although both the structure and total pressure loss that develop in the wake flow are comparable to those found for quasi-steady flow conditions, the developing flow reveals characteristics that are not found in the quasi-steady measurements. New data are also presented with regard to the character of the gust that develops in this wind tunnel and their impact upon the reported wake measurements is discussed.

It is well documented that the aerodynamic performance of an open wheel race car is degraded when closely following another car. The greatest performance loss is usually experienced by the front-mounted wing leading to reduced aerodynamic downforce, handling imbalance and a reduced overtaking capability. Although previous wind tunnel studies have been performed to investigate this race situation the model scales have generally been compromised in order to achieve representative separation between the two test vehicles within the confines of the wind tunnel working section and particularly within the limited length of the moving ground plane. This study addresses that issue by using a very short, bluff body to create an accurate representation of the wake flow from the leading car in order to provide additional, effective test length ahead of the instrumented model.