Complexity

Volume 2018, Article ID 3087312, 12 pages

https://doi.org/10.1155/2018/3087312

## Complexity Simulation on Application of Asymmetric Bionic Cross-Section Rod in Pantographs of High-Speed Trains

School of Mechatronic Engineering, Xi’an Technological University, Xi’an 710021, China

Correspondence should be addressed to Yan Cao; moc.361@zynotnaj

Received 25 May 2018; Accepted 11 July 2018; Published 1 August 2018

Academic Editor: Changzhi Wu

Copyright © 2018 Yan Cao et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

Ground transportation means and aircrafts with high-speed running are composed of many rod components. Aerodynamic noise generated therefrom is very outstanding. Reduction of the aerodynamic noise of rods becomes a hot topic in recent years. Most reported studies are tentative researches on aerodynamic noise of a pantograph or involve noise reduction of the pantograph with using porous materials or reshaping rod surfaces. Through using porous materials and reshaping rod surface, the aerodynamic noise of pantograph can be reduced to a certain extent, but the aerodynamic resistance will be increased and it is not convenient for practical application in engineering. Regarding this situation, the paper explores noise reduction performance of a feather on the back of a carrier pigeon and conducts the bionic design on rod surface. Through numerical simulation, the paper researches noise reduction performance of the bionic structure on the rod surface, reveals the mechanism of bionic noise reduction, and explores noise reduction effects of bionic structural rods on pantographs of the high-speed trains.

#### 1. Introduction

With the continuous increase of running speed, noise problems of high-speed trains become more and more obvious. When the running speed reaches over 250 km/h, the aerodynamic noise generated from high-speed train running will exceed wheel track noise and become the major noise source [1–4]. A pantograph is an equipment used by a high-speed train to obtain electric energy from a contact electric grid. It is composed of parts such as a slide plate and an arm rod. The complicated structure form of it brings huge influences on the aerodynamic performance of the high-speed train. When the train runs at a high speed, the concave and convex parts on the train will bring serious disturbance to airflows. As a result, complicated flow separation and a series of eddy shedding and crushing will take place, so that strong far-field aerodynamic pulsation pressure fields will be generated and transformed to aerodynamic noise. When the train running speed reaches 300 km/h, the aerodynamic noise of the pantograph will become the overriding noise source of high-speed railways. If the train speed is further increased, the aerodynamic noise of the pantograph will become more serious [5–8]. Reduction of pantograph aerodynamic noise has become one of the key technologies used to control the aerodynamic noise of high-speed trains [9–11].

At present, a lot of achievements have been achieved on simulation and reduction of aerodynamic noise of the high-speed train pantograph. King [12] used the dipole point acoustic source to describe aerodynamic noise caused by eddy shedding of the pantograph, finding the linear relationship between far-field aerodynamic noise of the pantograph and the logarithm of train speed. Noger et al. [13] tested the aerodynamic noise source of the pantograph in a low-noise wind tunnel, finding that the leeward side on the pantograph head is a major aerodynamic noise source. Sueki [14] used a porous material on the PS207 pantograph of a Shinkansen high-speed train and conducted a wind tunnel experiment, finding that noise was reduced by 1.9 dBA when the pantograph ran at 360 km/h. This result indicates that material attributes have great influences on the aerodynamic noise of the pantograph. Hence, material attributes shall be taken into account in a low-noise design of the pantograph. Kurita [15] optimized the structural shape of the pantograph head and adopted the novel low-noise pantograph. Noise reduction effects of the low-noise pantograph head shape and novel pantograph were verified in the wind tunnel experiment. Yu et al. [16] designed 3 fairing structures and carried out numerical simulation analysis of the pantograph, finding that noise reduction effects were obvious and the sound pressure level decreased by about 3 dB after the application of the fairing similar to a windshield structure. Liu et al. [17] adopted a hybrid computation method in which LIU used large eddy simulation to obtain the equivalent aerodynamic noise source of flow fields and then applied it on boundary elements of sound fields, so as to make detailed research of dipole noise source characteristics on the pantograph surface. It was found that the main energy of the pantograph ranged under 1000 Hz and was mainly centralized within 100~700 Hz. Under the certain train speed, with the increase of frequency, the amplitude of dipole noise source on the pantograph surface decreased. When the frequency increased from 20 Hz to 5000 Hz, the amplitude of dipole noise source under different train speeds decreased by over 30 dB. Xiao and Shi [11] carried out the simulation computation of different cross-section shapes of the pantograph insulator, finding the noise reduction rule that the optimal insulator cross-section shape is oval, and the long axis of oval shall accord with airflow direction. Zhang et al. [18] conducted numerical simulation researches on different structures and different installation positions of pantograph fairings as well as different arc-rise modes of the twin-type pantograph and other aspects, finding the optimal pantograph layout scheme that the far-field sound pressure level of a whole train can be reduced by 3.2 dBA to the most. Du et al. [19] used the separated eddy turbulence model and acoustic analogy theory to conduct far-field aerodynamic noise prediction of the simplified pantograph. Results show that the cross beam on the pantograph top is the main aerodynamic noise source. Lee and Cho [20] optimized the cross-section shape of the pantograph head and opened holes for drainage on the point pressure positions to reduce the airflow disturbance of the pantograph head. Wind tunnel testing results show that the improved pantograph shape can reduce disturbance at the tail part of the pantograph head and reduce aerodynamic noise.

Most studies above are tentative researches on the aerodynamic noise of the pantograph or involve the noise reduction of the pantograph with coating of porous materials or reshaping of rod surfaces. Through coating of porous materials and rod surface reshaping, the aerodynamic noise of the pantograph can be reduced to a certain extent, but the aerodynamic resistance will be increased and it is not convenient for practical application in engineering. The paper explores the noise reduction performance of the feather on the back of a carrier pigeon and conducts bionic reshaping design on the rod surface. Through numerical simulation, the paper researches the noise reduction performance of the bionic structure on the rod surface, reveals the mechanism of bionic noise reduction, and explores noise reduction effects of bionic structural rods on the pantograph of the high-speed train.

#### 2. Theory of Numerical Computation

The basic idea of LES is that spatial low-pass filtering is conducted to turbulence; N-S equation is solved directly for large-scale values; momentum and energy transport effects of small-scale eddies on large-scale eddies are simulated by a subgrid scale model. During transmission of turbulence energy, large-scale eddies nearly contain all the turbulence energy, while small-scale eddies mainly dissipate turbulence energy. Through direct computation of large-scale eddies, most flow information in turbulence motion can be kept. In addition, large-scale eddies are closely correlated with geometric boundary conditions of flow. Small-scale eddies are approximately isotropous and are deemed to suffer little influences from geometric boundaries and large-eddy motion. Hence, application of the subgrid mode in the simulation of small-scale eddies is applicable to various types of turbulence motion. It is fair to say that the LES method is a neural method between DNS and RANS. In comparison with the RANS method, the LES method can further reflect true details of turbulence, so high computation accuracy can be ensured. The control equation of LES is still the N-S equation of incompressible fluids. The large-scale speed in LES is the smoothing speed, which is defined as where is a smoothing function, which is used to calibrate large eddies and filter out small eddies and denotes the size of the filtering mesh. It is assumed that the filtering course and the derivation course can be changed. It is applied to the N-S equation of the incompressible fluid. Regardless of the form of , we can obtain

It is set that , so Formula (2) can be changed into

The subgrid scale Reynolds stress is an unknown quantity needing to be modeled. It is assumed that

Formula (5) denotes the small-scale motion. The speed resolution formula is substituted into the expression of the subgrid scale Reynolds stress, so

In the above equations, is the space position, is the computational time, is the coordinate in the direction, is the velocity in the direction, is the coordinate in the direction, is the velocity in the direction, is the derivative, is the density, is the pressure, is the subgrid scale Reynolds stress, and is the turbulent viscosity coefficient. In the equation, the first item denotes the Leonard item, namely, the interaction between two large eddies, which can generate small-scale turbulence. The second item is a crossover item which represents the interaction between large and small eddies, wherein the energy between them can be transmitted from large eddies to small eddies. It can also be transmitted reversely from small eddies to large eddies. However, as an average whole, the energy is mainly transferred from large eddies to small eddies. The third item is the antiscatting item, representing the interaction between small eddies, which can generate large eddies and lead to the transmission of energy from small eddies to large eddies.

#### 3. Flow Noise of Bionic Asymmetric Cross-Section Rod

##### 3.1. Model of Bionic Asymmetric Cross-Section Rod

A carrier pigeon is a kind of flying animal. Its flying speed can reach up to 177 km/h [21–24]. In general, a carrier pigeon flies at 80 km/h. This speed is roughly equivalent to 75 times the length of the pigeon per second. A carrier pigeon has a streamline body, strong wings, and soft feather. For these characteristics, they can fly freely in the air. Carrier pigeons can fly far very quickly, indicating that they can effectively solve the problem of energy saving and resistance reduction in air medium motion. This is closely correlated with the unique surface appearance and special forms of feather surface. The diethyl ether solution was used to narcotize an experimental carrier pigeon. The epidermis with a feather was taken out from the back of the carrier pigeon. The epidermis was spread and fixed on a plane with the same size of the epidermis. Here, a specimen was made. Planar image collection was conducted to the specimen. As for the collection method, images were shot by a digital camera at first. Then, different multiples of images of the specimen were collected under the microscope. Finally, the surface appearance image of the carrier pigeon can be obtained, as shown in Figure 1(a). Each feather presents a surface structure which is formed through tile-tail covering from outside to inside. The root of each feather is covered by the tail end of the feather of the previous row. They are arranged in a staggered manner. The overlaid arrangement between feathers forms a curved groove structure and an overlaid curved edge line structure. The curvature of the curved groove and the curved edge line is the same with that of feather edges. King and Pfizenmaier [25] conducted aerodynamic noise testing of rods with different cross-section shapes, finding that the aerodynamic noise of the oval cross-section rod was lower than that of other cross-section rods. In combination with feather edge curved lines in Figure 1(a), the bionic asymmetric cross-section was established, as shown in Figure 1(b). As a whole, the rod cross-section is approximate to an oval structure.