When the fluid inside a completely filled cylinder is set in motion by the rotation of one endwall, steady and unsteady axisymmetric vortex breakdown is possible. Nonlinear dynamical systems theory is used to describe the changing kinematics of the flow as the speed of the rotating endwall is increased. Two distinct modes of oscillation have been found in the unsteady regime and the chaotic advection caused by the oscillations has been investigated. The results of this study are used to describe the filling and emptying processes of the vortex breakdown bubbles observed in flow visualization experiments.

As vehicle manufacturers work to reduce energy consumption of all types of vehicles, external vehicle aerodynamics has become increasingly important. Whilst production vehicle shape optimisation methods are well developed, the need to make further advances requires deeper understanding of the highly three-dimensional flow around bluff bodies. In this paper, the wake flow of a generic bluff body, the Windsor body, based on a square-back car geometry, was investigated by means of balance measurements, surface pressure measurements and 2D particle image velocimetry planes. Changes in the wake topology are triggered by the application of short tapers (4 % of the model length) to the top and bottom edges of the base, representing a shape optimisation that is realistic for many modern production vehicles. The base drag is calculated and correlated with the aerodynamic drag data. The results not only show the effectiveness of such small devices in modifying the time average topology of the wake but also shed some light on the effects produced by different levels of upwash and downwash on the bi-stable nature of the wake itself.

Author, co-author (Do NOT enter this information. It will be pulled from participant tab in MyTechZone)Affiliation (Do NOT enter this information. It will be pulled from participant tab in MyTechZone) AbstractThis paper looks into the effect on base pressure of applying a high aspect ratio chamfer to all edges of a simplified squareback model (the Windsor model). The effects are investigated using force and moment measurements along with surface pressure measurements on the slanted surface and vertical base. The work forms part of a larger study to develop understanding of the mechanisms that influence overall base pressure and hence the resulting aerodynamic drag.A short slant (approx. 4% of model length) was applied to the trailing edges of the simplified vehicle model, representing the small rear end optimisation typical of many real vehicle geometries. Two experiments were performed: the first applied a chamfer at varying angles to the top and bottom edges; the second test looked at the same chamfer angle applied to the sides of the model geometry while the top and bottom angle remained square. The changes in drag are discussed and explained in the context of the base pressures and area weighted pressure coefficients.

The use of simulation tools by vehicle manufacturers to design, optimize and validate their vehicles is essential if they are to respond to the demands of their customers, to meet legislative requirements and deliver new vehicles ever more quickly. The use of such tools in the aerodynamics community is already widespread, but they remain some way from replacing physical testing completely. Further advances in simulation capabilities depend on the availability of high quality validation data so that simulation code developers can ensure that they are capturing the physics of the problems in all the important areas of the flow-field. This paper reports on an experimental program to generate such high quality validation data for a SAE 20 degree backlight angle notchback reference model. This geometry is selected as a particularly powerful test case for the development and validation of numerical tools because the flow exhibits a realistic impingement and A pillar regime, significant three dimensional structures and the backlight/boot-deck exhibits a local separation and reattachment. The paper includes force and moment data, surface pressures for the centerline, slant, boot-deck and base and detailed PIV data for the impingement region, model centerline, A pillar and multiple planes on the slant and boot-deck. Time averaged, statistical and instantaneous data are presented.Results are discussed with regard to the overall flow features, the correlation between the different data sets and the accuracy and limitations of each of the experimental techniques in this particular application. Example data is included throughout the paper and full data sets are freely available in the Loughborough University Institutional Repository as a resource for future code development.

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