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The wake of a fastback type passenger vehicle is characterised by trailing vortices from the rear pillars of the vehicle. These vortices strongly influence all the aerodynamic coefficients. Working at model scale, using two configurations of the Davis model with different rear pillar radii, (sharp edged and 10mm radius) the flow fields over the rear half of the models were investigated using balance measurements, flow visualisations, surface pressure and PIV (Particle Image Velocimetry) measurements. For a small geometry change between the two models, the changes to the aerodynamic loads and wake flow structures were unexpectedly large with significant differences to the strength and location of the trailing vortices in both the time averaged and unsteady results. The square edged model produced a flow field similar to that found on an Ahmed model with a sub-critical backlight angle. The round edged model produced a flow structure dominated by trailing vortices that mix with the wake behind the base of the model and are weaker. This flow structure was more unsteady than that of the square edged model. Consequently, although both models can be described as having a wake dominated by trailing vortices, there are significant differences to both the steady state and unsteady flow fields that have not been described previously. This also shows that the fastback wake structure described by Ahmed is not definitive. , trailing vortices, unsteadiness, Davis model, Ahmed model, fastback Wake

This paper investigates the influence that different unsteady aerodynamic components have on a vehicle's handling. A simulated driver and vehicle are subject to two time-dependent crosswinds, one representative of a windy day and the second an extreme crosswind gust. Initially a quasi-static response is considered and then 5 additional sources of aerodynamic unsteadiness, based on experimental results, are added to the model.From the simulated vehicle and driver, the responses are used to produce results based on lateral deviation, driver steering inputs and also to create a 'subjective' handling rating. These results show that the largest effects are due to the relatively low frequency, time-dependent wind inputs. The additional sources of simulated unsteadiness have much smaller effect on the overall system and would be experienced as increased wind noise and reduced refinement rather than a worsening of the vehicle's handling. KeywordsUnsteady Aerodynamics, Vehicle Dynamics, Driver Model, Crosswinds, Vehicle Handling

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This paper investigates the surface pressures found on the sides of a Davis model under steady state conditions and during yawed oscillations at a reduced frequency which would generally be assumed to give a quasi-static response. The surface pressures are used to investigate the flow field and integrated to infer aerodynamic loads. The results show hysteresis in the oscillating model's results, most strongly in the A-pillar flows. The changes to the flow field reduce strength of the flows around the rear pillars, reduce the strength and extent of the A-pillar vortex and cause the surface pressures to couple with the oscillating motion. This work shows the flows around the front of a vehicle may be more important to a vehicle's unsteady aerodynamics than is generally accepted and also leads to the conclusions that the reduced frequency parameter may not fully describe the onset unsteadiness.