An LES Investigation of the Near-Wake Flow Topology of a Simplified Heavy Vehicle

Anirudh N. Rao,Branislav Basara,Guglielmo Minelli,Siniša Krajnović,Jie Zhang

doi:10.1007/s10494-018-9959-6

Abstract

Recent experimental investigations by McArthur et al. (J. Fluids Struct. 66, 293–314, 2016) in the wake of a simplified heavy vehicle or commonly known as the ground transportation system (GTS) model has shown that the flow topology is invariant over a large range of Reynolds numbers [2.7 × 104 − 2 × 106]. Numerical simulations are performed to investigate the initial flow topology at a Reynolds number of 2.7 × 104, using well-resolved large eddy simulations (LES). In the vertical midplane behind the GTS, a flow state which is anti-symmetric to that reported in McArthur et al. (J. Fluids Struct. 66, 293–314, 2016) is observed here, thereby, confirming the possibility of occurrence of the complementary bi-stable flow state. The occurrence of this bi-stable state does not depend on the ground clearance between the GTS and the ground plane, as a similar flow topology is observed at both small and large gap heights. Furthermore, the flow topology in the vertical midplane is also found to be insensitive to the incoming flow for small yaw angles. However, complex flow behaviour is observed in the wake for larger yaw angles, where the flow topology in the vertical midplane becomes nearly symmetric, while an asymmetric flow topology is now observed in the lateral midplane in the near wake. Furthermore, the corner vortices which originate from either side at the front of the model merge in the far wake, leading to a large vortex structure nearly equal to the height of the model. The near-wake topology of the GTS is analysed and compared with previous studies for a range of scenarios, and the forces on the GTS are computed.

Highlights

The ground transportation system (GTS) model is a simplified cab-over-engine truck model and is representative of a tractor-trailer combination without any intermediate gap
A similar investigation by [65] using Reynolds-averaged Navier–Stokes (RANS) models failed to accurately capture the asymmetrical flow field in the vertical midplane of the model, the Wilcox 1988 k − ω model showed a larger degree of asymmetry as compared to the SA and the Mentor SST models
The results show that the locations of the vortex centres of the medium mesh are closer to the base as compared to the coarse and fine mesh, while those observed for the gap height of 1.1H are closer to its counterparts of the fine mesh for the GTS at a gap height of 0.14H

Summary

Introduction

The ground transportation system (GTS) model is a simplified cab-over-engine truck model and is representative of a tractor-trailer combination without any intermediate gap. The earliest experimental investigations of the GTS model by [10] and [71] were performed with the aim of reducing drag by the use of active and passive flow control devices (several addon devices such as slanted rear end and boat-tails to the base of the model) ([4, 8, 9, 14, 28, 44, 47, 54], and others). Roy et al [63] obtained steady state solutions at Re = 2 × 106 using Reynolds-averaged Navier–Stokes (RANS) k − ω Menter model and Spalart-Allmaras (SA) model. They assessed the capability of these model by comparing the flow structures and surface pressure data obtained from the work of [71]. A similar investigation by [65] using RANS models failed to accurately capture the asymmetrical flow field in the vertical midplane of the model, the Wilcox 1988 k − ω model showed a larger degree of asymmetry as compared to the SA and the Mentor SST models

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Methods

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Conclusion