Since recent years governmental legislation and consumer demands are driving the development of more energy efficient road vehicles. One of the aspects considered when increasing efficiency is the aerodynamic performance of the vehicle. The focus of this paper is on side wind effects on drag on a vehicle with tapered rear extensions. For this, numerical simulations are analysed using post-processing techniques such as Proper Orthogonal Decomposition (POD) and Two-point correlation.The extensions protrude 150mm from the perimeter of the base and are investigated in two configurations: with a smooth taper and with an added kick, which realigns the perimeter base flow to the vehicle's driving direction.As the incoming flow angle is increased drag increases for the investigated angles. The smooth extensions provide the greatest drag improvement at 0°-yaw while the extensions with a kick yield addition benefit at yaw, effectively reducing the vehicles drag sensitivity to side wind. A large scale twisting motion is present at yaw for the baseline and smooth extensions configurations which is reduced when adding a kick to the extension.
Governmental regulations and increased consumer awareness of the negative e ects of greenhouse gases has led the automotive industry to massive invest in the energy e ciency of its fleet. One way towards accomplishing reduced fuel consumption is minimizing the drag of vehicles by improving its aerodynamics. Fuel consumption is measured by standardized driving cycles which do not consider aerodynamic losses during cornering. It is uncertain whether cornering has a significant impact on the drag, and the present study intends to investigate this numerically, using a generic vehicle model called the DrivAer. The model is considered in two di erent configurations: the notchback and the squareback. Cornering in various radiuses is modelled using a Moving Reference Frame approach which provides the correct flow conditions when simulating a stationary vehicle where the wind and ground are moving instead. Simulations are also performed for straight ahead driving conditions to provide data for comparison to a cornering vehicle. Results indicate that the drag increases when the cornering radius is small. This implies a higher fuel consumption than the standardized driving cycles suggest using straight-ahead drag coe cients. The detailed underbody of the DrivAer model is not symmetrical which, for large turning radiuses, results in a decrease of drag for left turns, while turning right results in an increase of drag. Cornering a ects the squareback and the notchback similarly, although the squareback experiences a slightly higher drag throughout the cases investigated.
Regulations on global greenhouse gas emission are driving the development of more energy-efficient passenger vehicles. One of the key factors influencing energy consumption is the aerodynamic drag where a large portion of the drag is associated with the base wake. Environmental conditions such as wind can increase the drag associated with the separated base flow. This paper investigates an optimised yaw-insensitive base cavity on a square-back vehicle in steady crosswind. The test object is a simplified model scale bluff body, the Windsor geometry, with wheels. The model is tested experimentally with a straight cavity and a tapered cavity. The taper angles have been optimised numerically to improve the robustness to side wind in relation to drag. Base pressures and tomographic Particle Image Velocimetry of the full wake were measured in the wind tunnel. The results indicate that a cavity decreases the crossflow within the wake, increasing base pressure, therefore lowering drag. The additional optimised cavity tapering further reduces crossflow and results in a smaller wake with less losses. The overall wake unsteadiness is reduced by the cavity by minimising mixing in the shear layers as well as dampening wake motion. However, the coherent wake motions, indicative of a balanced wake, are increased by the investigated cavities.
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