Influence of Base Slant on the Wake Structure and Drag of Road Vehicles

Ahmed, Shehzad

doi:10.1115/1.3241024

Cited by 75 publications

(31 citation statements)

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“…Moving road vehicles induce a range of aerodynamic flow features which include: separation bubbles, edge and horseshoe vortices, separating shear layers and eddying turbulent wake structures [27,28]. The presence of a moving ground plane (relative to the vehicle) and rotating wheels introduce further complexity which makes the simulation of road vehicle aerodynamics a non-trivial exercise.…”

Section: Ahmed Bodymentioning

confidence: 99%

Dealing with numerical noise in CFD-based design optimization

Gilkeson¹,

Торопов²,

Thompson³

et al. 2014

Computers & Fluids

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SUMMARYNumerical noise is an inevitable by-product of Computational Fluid Dynamics (CFD) simulations which can lead to challenges in finding optimum designs. This article draws attention to the issue, illustrating the difficulties it can cause for road vehicle aerodynamics simulations. Firstly a benchmark problem is used to assess a range of turbulence models and grid types. Large noise amplitudes up to 22% are evident for solutions computed on unstructured tetrahedral grids whereas computations on hexahedral and polyhedral grid structures exhibit substantially less noise. The Spalart Allmaras turbulence model is shown to be far less susceptible to noise levels than two other commonly-used models for this application.Secondly, multi-objective aerodynamic shape optimization is applied to a fairing for a practical road vehicle which is parameterised in terms of three design variables. Moving Least Squares (MLS) metamodels are constructed from 50 highfidelity CFD solutions for two objective functions. Subsequent optimization is successful for the first objective, however numerical noise levels in excess of 7% give rise to difficulties for the second one. A revision to the problem leads to success and the construction of a small Pareto Front. Further analysis underlines the inherent capability of MLS metamodels in dealing with noisy CFD responses.

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Section: Ahmed Bodymentioning

confidence: 99%

Dealing with numerical noise in CFD-based design optimization

Gilkeson¹,

Торопов²,

Thompson³

et al. 2014

Computers & Fluids

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“…Those have a very negative effect on the high-speed trains, which not only increases the pressure drag between the head and tail, but also seriously affects the lift and side force of the tail, causing the tail swinging more intensely. A pair of counter-rotating vortices occurs at many similar flow, such as blunt body's wake area, the modern car's wake area, et al It was discovered by Ahmed in the study of its generic road vehicle models [3] , and other researchers, like Vino and Krajnovic, also found the downward and outward movement of this pair of vortices [4,5] . Schulte-Werning used the commercial software Fluent to study the unsteady flow characteristics of the ICE2 trailing vortex, and obtained the streamlines on the surface of ICE2 tail in a vortex shedding cycle [6] , revealing the production mechanism of the side force of the train.…”

Section: Introductionmentioning

confidence: 99%

Effects of Different Train Speeds on the Dynamics of Wake Flow of a Full-Scaled High-Speed Train

Li¹,

Guo²,

Yang³

2017

dtetr

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The wake flow of high-speed train is an extremely complicated three-dimensional unsteady flow due to the vortices generated and shed from the trailing car periodically, which has great influence on the aerodynamic performance of the trailing car, such as comfortable performance and safety. In this paper, the dynamic characteristics of trailing vortices of a full-scaled model of CRH380A high-speed trains, consisting of a locomotive, a middle car and a trailing car, at different speeds is studied with delayed-detached eddy simulation (DDES). Two large helical vortices exist in the wake flow field and move sinusoidally and anti-symmetrically. As the speed increases, the ground effect on the wake flow is more obvious, the cores' height of the trailing vortices from the ground become much higher, and the intensity of the trailing vortices becomes much greater. In addition, the unsteady wake flow field is decomposed by proportional orthogonal decomposition method (POD). It is found that the vertex positions in the same mode shift at different speeds, but the overall spatial structure is similar. The periodicity and corresponding frequencies of different POD modes at different speeds are ________________________ 597obtained by analyzing the snapshots of POD modes, which are also compared with the FFT results of mode coefficients. It is found that the frequencies of modes 2 and 3 are approximately equal at each velocity, and the frequency of mode 4 is approximately twice as much as them.

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“…Looking into the literature shows that many notchback like geometry studies were done on simplified shapes and generic bodies [2,3,5,9,10,11,12]. These investigations show that the flow field is different, as for instance vortices are different in size and position, but on the other hand main features like saddle points and foci are present in a similar way for the different geometries.…”

Section: Introductionmentioning

confidence: 99%

“…The investigation of geometric parameters like the backlight angle, effective backlight angle, trunk deck length and the relation to each other give indications for an improved vehicle shape [9,10,11,15,16].…”

Section: Introductionmentioning

confidence: 99%

Investigations of the Rear-End Flow Structures on a Sedan Car

Kounenis

Bonitz

Ljungskog

et al. 2016

SAE Technical Paper Series

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The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. AbstractThe aerodynamic drag, fuel consumption and hence CO 2 emissions, of a road vehicle depend strongly on its flow structures and the pressure drag generated. The rear end flow which is an area of complex three-dimensional flow structures, contributes to the wake development and the overall aerodynamic performance of the vehicle.This paper seeks to provide improved insight into this flow region to better inform future drag reduction strategies. Using experimental and numerical techniques, two vehicle shapes have been studied; a 30% scale model of a Volvo S60 representing a 2003MY vehicle and a full scale 2010MY S60.First the surface topology of the rear end (rear window and trunk deck) of both configurations is analysed, using paint to visualise the skin friction pattern. By means of critical points, the pattern is characterized and changes are identified studying the location and type of the occurring singularities. The flow field away from the surface is then analysed using PIV measurements and CFD for the scale model and CFD simulations for the full scale vehicle. The flow field is investigated regarding its singular points in cross-planes and the correlation between the patterns for the two geometries is analysed.Furthermore, it is discussed how the occurring structures can be described in more generalized terms to be able to compare different vehicle geometries regarding their flow field properties.The results show the extent to which detailed flow structures on similar but distinct vehicles are comparable; as well as providing insight into the complex 3D wake flow.

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Influence of Base Slant on the Wake Structure and Drag of Road Vehicles

Cited by 75 publications

References 0 publications

Dealing with numerical noise in CFD-based design optimization

Dealing with numerical noise in CFD-based design optimization

Effects of Different Train Speeds on the Dynamics of Wake Flow of a Full-Scaled High-Speed Train

Investigations of the Rear-End Flow Structures on a Sedan Car

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