The near-wake of an axisymmetric body has been investigated using base pressure tappings and large scale Tomographic Particle Image Velocimetry (TPIV) at a Reynolds number of ReD = 3.2 × 105, based upon model diameter. Insights into the near-wake dynamics are provided by the application of Proper Orthogonal Decomposition (POD) to the pressure and the TPIV datasets. The first two POD modes show that the axisymmetric topology seen in the time averaged field is the result of the combination of different reflectional symmetry preserving states, each one featuring a hairpin vortex surrounded by an annular structure developing in proximity to the wake closure. The “head” and the “tails” of each hairpin vortex appear to be dynamically linked, as also proven by the existence of a second pair of modes, visible only in the TPIV dataset, featuring a twisted two-lobe structure. The analysis of the temporal evolution of the radial position of the centre of pressure over the model base reveals the existence of two different low-drag scenarios, characterised by the restoration of the axial symmetry or the selection of a single plane of reflectional symmetry. The first state is reported to become the only admissible low-drag configuration when the short-time wake dynamics are removed from the unsteady pressure signal.
As the automotive industry strives to increase the amount of digital engineering in the product development process, cut costs and improve time to market, the need for high quality validation data has become a pressing requirement. While there is a substantial body of experimental work published in the literature, it is rarely accompanied by access to the data and a sufficient description of the test conditions for a high quality validation study. This paper addresses this by reporting on a comprehensive series of measurements for a 25% scale model of the DrivAer automotive test case. The paper reports on the measurement of the forces and moments, pressures and off body PIV measurements for three rear end body configurations, and summarises and compares the results. A detailed description of the test conditions and wind tunnel set up are included along with access to the full data set.
Sports Utility Vehicles (SUVs) often have blunt rear end geometries for design and practicality, which is not typically aerodynamic. Drag can be reduced with a number of passive and active methods, which are generally prioritised at zero yaw, which is not entirely representative of the "on road" environment. As such, to combine a visually square geometry (at rest) with optimal drag reductions at non-zero yaw, an adaptive system that applies vertical side edge tapers independently is tested statically.A parametric study has been undertaken in Loughborough University's Large Wind Tunnel with the ¼ scale Windsor Model. The aerodynamic effect of implementing asymmetric side tapering has been assessed for a range of yaw angles ( ∘ , ± . ∘ , ± ∘ and ± ∘ ) on the force and moment coefficients. This adaptive system reduced drag at every non-zero yaw angle tested, from the simplest geometry (full body taper without wheels) to the most complex geometry (upper body taper with wheels) with varying levels of success; providing additional drag reductions from 3% to 125%. The system also shows potential to beneficially modify the cross wind stability of the geometry.
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