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University of Southampton Research Repository ePrints Soton Copyright © and Moral Rights for this thesis are retained by the author and/or other copyright owners. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the copyright holder/s. The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the copyright holders. When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given e.g. AUTHOR (year of submission) "Full thesis title", University of Southampton, name of the University School or Department, PhD Thesis, pagination http://eprints.soton.ac.uk UNIVERSITY OF SOUTHAMPTON Faculty of Engineering and the Environment Aeronautics, Astronautics and Computational Engineering Aerodynamic Noise of High-speed Train Bogies by Jianyue Zhu Thesis for the degree of Doctor of Philosophy June 2015 UNIVERSITY OF SOUTHAMPTON ABSTRACT FACULTY OF ENGINEERING AND THE ENVIRONMENT Aeronautics, Astronautics and Computational Engineering Thesis for the degree of Doctor of Philosophy AERODYNAMIC NOISE OF HIGH-SPEED TRAIN BOGIES Jianyue Zhu For high-speed trains, aerodynamic noise becomes significant when their speeds exceed 300 km/h and can become predominant at higher speeds. Since the environmental requirements for railway operations will become tighter in the future, it is necessary to understand the aerodynamic noise generation and radiation mechanism from high- speed trains by studying the flow-induced noise characteristics to reduce such environmental impacts. The aim of this thesis is to investigate the flow behaviour and the corresponding aeroacoustic mechanisms from high-speed trains, especially around the bogie regions. Since the prediction of the flow-induced noise in an industrial context is difficult to achieve, this study focuses on scale models with increasing complexity. The aerodynamic and aeroacoustic behaviour of the flow past an isolated wheelset, two tandem wheelsets, a simplified bogie and the bogie inside the cavity with and without the fairing as well as considering the influence of the ground are investigated at a scale 1:10. A two-stage hybrid method is used consisting of computational fluid dynamics and acoustic analogy. The near-field unsteady flow is obtained by solving the Navier-Stokes equations numerically through the delayed detached-eddy simulation and the source data are applied to predict the far-field noise signals using the Ffowcs Williams-Hawkings acoustic analogy. All simulations were run with fully structured meshes generated according to the guidelines based on a grid independence study on a circular cylinder case. Far-field noise radiated from the scale models was measured in an open-jet anechoic wind tunnel. Good agreement is achieved between numerical simulations and experimental measurements for the dominant frequency of tonal noise and the shape of the spectra. Numerical results show that turbulent flow past the isolated wheelset is dominated by three-dimensional vortices. Vortex shedding around the axle is the main reason for the tonal noise generation with the dominant peak related to the vortex shedding frequency. The noise directivity shows a typical dipole pattern. Moreover, for both the tandem-wheelset and the simplified bogie cases, the unsteady flow developed around them is characterized by the turbulent eddies with various scales and orientations including the coherently alternating shedding vortices generated from the upstream axles. The vortices formed from the upstream geometries are convected downstream and impinge on the downstream bodies, generating a turbulent wake i behind the objects. Vortex shedding and flow separation as well as interaction around the bodies are the key factors for the aerodynamic noise generation. The radiated tonal noise corresponds to the dominant frequencies of the oscillating lift and drag forces from the geometries. The directivity exhibits a distinct dipole shape for the noise radiated from the upstream wheelset whereas the noise directivity pattern from the downstream wheelset is multi-directional. Compared to the wheelsets, the noise contribution from the bogie frame is relatively small. Furthermore, when the bogie is located inside the bogie cavity, the shear layer developed from the cavity leading edge has a strong interaction with the flow separated from the upstream bogie and cavity walls. Thus a highly irregular and unsteady flow is generated inside the bogie cavity due to the considerably strong flow impingement and interaction occurring there. Unlike the isolated bogie case, noise spectra from the bogie inside the cavity are broadband and a lateral dipole pattern of noise radiation is generated. The noise prediction based on the permeable surface source is formulated and programmed using the convective Ffowcs Williams-Hawkings method. Results show that the bogie fairing is effective in reducing the noise levels in most of the frequency range by mounting a fairing in the bogie area; and for the bogie inside the bogie cavity with the ground underneath, the far-field noise level is increased due to more flow interactions around the geometries and the ground reflection effect. ii Contents 1 Introduction ................................................................................................................ 1 1.1 Background ................................................................................................................. 1 1.2 Research Objectives ................................................................................................... 3 1.3 Structure of Thesis ..................................................................................................... 3 2 Literature Review ..................................................................................................... 5 2.1 Aeroacoustic Research on High-speed Trains .......................................................... 5 2.1.1 Bogie ..................................................................................................................... 6 2.1.2 Pantograph ......................................................................................................... 10 2.1.3 Pantograph recess ............................................................................................. 11 2.1.4 Inter-coach spacing ........................................................................................... 12 2.1.5 Nose of power car .............................................................................................. 13 2.1.6 Rear power car ................................................................................................... 14 2.1.7 Coach wall surfaces ........................................................................................... 14 2.1.8 Ventilators, louvres and cooling fans............................................................... 15 2.1.9 Concluding remarks .......................................................................................... 16 2.2 Theory on Aerodynamic Noise Prediction using Acoustic Analogy ...................... 16 2.2.1 General sound sources ...................................................................................... 17 2.2.2 Lighthill’s theory: acoustic analogy .................................................................. 17 2.2.3 Curle’s theory: effect of solid boundaries ....................................................... 21 2.2.4 Ffowcs Williams-Hawkings method: effect of source motion ......................... 22 2.2.5 Theory of vortex sound ..................................................................................... 25 2.3 Numerical Methods for Aeroacoustics .................................................................... 25 2.3.1 Direct computation methods ............................................................................ 26 2.3.2 Integral methods based on acoustic analogy .................................................. 27 2.3.3 Empirical methods ............................................................................................. 30 2.4 Experimental Techniques for Aerodynamics and Aeroacoustics .......................... 31 2.4.1 Wind-tunnel measurements .............................................................................. 31 2.4.2 Field and on-board measurements ................................................................... 35 2.5 Summary ................................................................................................................... 36 3 Research Description ........................................................................................... 37 3.1 Research Outline ....................................................................................................... 37 3.2 Numerical Approach ................................................................................................. 38 3.2.1 Computational mesh generation ...................................................................... 39 iii 3.2.2 CFD solution process ........................................................................................ 40 3.2.3 Far-field noise prediction .................................................................................. 47 3.2.4 Post-processing of simulation