PARAMETRIZATION OF HIGH-SPEED TRAIN STREAMLINE SHAPE

In the past decade, the high speed trains (HSTs) in China have experienced a booming development, with the design of CRH380A as a predominant example. A series of brand new HSTs have been developed with high aerodynamic performance, which includes the running resistance, the lift of the trailing car, pressure waves when trains pass by each other, aerodynamic noise in the far field, etc. In order to design HSTs with better aerodynamic performance, it is necessary to perform aerodynamic shape optimization, especially to optimize the streamline shape of HSTs. Parametrization is the basis for the whole optimization process, since good parametrization approach not only affects the optimization strategy, but also determines the design space and optimization efficiency. In the present paper, a series of work related to the streamline shape parametrization performed by the author in recent years have been introduced. Four different parametrization approaches have been exhibited, which are Local Shape Function method (LSF) and Free-Foam Deformation method (FFD), Modified Vehicle Modeling Function method (MVMF), Class function/Shape function Transformation method (CST). These methods could be categorized into two kinds: shape disturbance approach (LSF and FFD) and shape description approach (MVMF and CST). Among these four methods, some are developed by the authors while some are locally modified so as to meet the parametrization of the streamline shape. The detailed process of these four approaches are exhibited in the present paper and the characteristics of these four approaches are compared.</p

Surrogate Based Optimization of Aerodynamic Noise for Streamlined Shape of High Speed Trains

Aerodynamic noise increases with the sixth power of the running speed. As the speed increases aerodynamic noise becomes predominant and begins to be the main noise source at a certain high speed. As a result aerodynamic noise has to be focused on when designing new high-speed trains. In order to perform the aerodynamic noise optimization the equivalent continuous sound pressure level (SPL) has been used in the present paper which could take all of the far field observation probes into consideration. The Non-Linear Acoustics Solver (NLAS) approach has been utilized for acoustic calculation. With the use of Kriging surrogate model a multi-objective optimization of the streamlined shape of high-speed trains has been performed which takes the noise level in the far field and the drag of the whole train as the objectives. To efficiently construct the Kriging model the cross validation approach has been adopted. Optimization results reveal that both the equivalent continuous sound pressure level and the drag of the whole train are reduced in a certain extent

Study on the critical diameter of the subway tunnel based on the pressure variation

When the subway train operates at a speed higher than 100 km/h, the corresponding aerodynamic issue becomes severe. To meet the future requirement for the speedup of subway trains, a research on the critical diameters of the subway tunnel for trains operating at 120 and 140 km/h has been performed based on passengers' aural discomfort caused by rail tunnel pressure variation. A three-dimensional computational fluid dynamic approach has been adopted for analysis. Meanwhile, trains with different airtight indices are considered and the pressure variations inside and outside the trains are both under investigation. Based on the corresponding criteria for different airtight indices, critical tunnel diameters for trains running at different speeds have been determined. This study would aid in the tunnel section design for future high-speed subway trains

Optimization design for aerodynamic elements of high speed trains

The complex wake flow of high speed trains severely influences the running safety and amenity of the trailing car. In this paper, based on the streamlined shape of CRH380A high speed train, taking the aerodynamic lift force of the trailing car and the volume of the streamlined head as the objectives, an efficient multi-objective optimization process based on the response surface has been constructed. The Kriging model has been constructed based on the cross-validation method and genetic algorithm (GA). This approach could decrease the number of training samples and improve the optimization efficiency while without decreasing its generalization. After the Pareto optimal solutions being obtained, four design points are chosen for comparative study with the original shape, and one of these points is chosen for the unsteady aerodynamic study together with the original shape. The results reveal that the variation trends of the lift force and the side force of the trailing car are the same as that of the drag of the whole train. After optimization, the volume of the streamlined head is almost the same as that of the original shape. Compared to the original shape, the lift force of the trailing car decreases by 27.86% of and the drag of the whole train decreases by 3.34% in conditions without crosswind, and the lift force of the trailing car decreases by 5.43%, the side force of the whole train decreases by 72.09% and the drag of the whole train decreases by 2.1% in the crosswind conditions. The optimal train benefits from low fluctuations of lift and side force of the trailing car. Besides, better wake flow could be obtained, and the wake vortices are suppressed, too. Consequently, the running safety and amenity of HST are improved a lot after optimization. (C) 2014 Elsevier Ltd. All rights reserved

RESEARCH ON RUNNING STABILITY OF CRH3 HIGH SPEED TRAINS PASSING BY EACH OTHER

Two scenarios of trains passing by each other are usually encountered, which are trains passing by each other in the tunnel and passing by each other in the open air, respectively. The prototype of the CRH3 high speed train is considered in the present paper, with bogies, windshields, pantograph shrouds, air conditioner shrouds and other complex structures taking into consideration. Aerodynamic loads and multi-body system response of this prototype are discussed under the conditions of both scenarios. The variations of aerodynamic loads and the pressure on the surface of the trains are mainly analyzed, and then the formation mechanism of the variations is discussed. A comparative study of the differences in both scenarios is also performed. In addition, the dynamic response of the high speed train has been studied by loading the unsteady aerodynamic forces and torques. Furthermore, the derailment coefficient, the wheel unloading rate, the wheel/rail lateral force and the wheel/rail vertical force are analyzed as assessment criteria to verify the running stability in the two scenarios. The most unsafe position during the process of trains passing by each other and the variation of the four parameters with the speed is obtained. Then the linear fit between the four parameters and the speed has been performed, and the limiting speed under these two scenarios are also obtained. As a result, the results of this paper could provide guidance for safe running of trains passing by each other in reality

Identification and suppression of noise sources around high speed trains

Aerodynamic noise would become a significant limiting factor as the running speed of high speed trains increases, and should be taken into consideration during the design of high speed trains. In the present work, the Nonlinear Acoustics Solver (NLAS) has been adopted to investigate the aerodynamic noise of high speed trains. The region around the streamlined head of the leading car and the trailing car, the bogie region, the upstream zone and the wake zone are discussed and the distribution characteristics of aerodynamic noise sources around a high speed train is exhibited. The acoustic characteristics of the streamlined head could be contaminated due to the unreasonable arrangement of cab windows or cowcatchers. As a result, different designs of cab windows and cowcatchers are investigated in this paper and advice on low noise design is given. Based on the above analysis, a new design of the streamlined head is proposed. Numerical results reveal that the noise level of the new streamline has been greatly suppressed. The analysis would aid in identification of noise sources around high speed trains and design of high speed trains with low noise

Numerical study on wake characteristics of high-speed trains

Intensive turbulence exists in the wakes of high speed trains, and the aerodynamic performance of the trailing car could deteriorate rapidly due to complicated features of the vortices in the wake zone. As a result, the safety and amenity of high speed trains would face a great challenge. This paper considers mainly the mechanism of vortex formation and evolution in the train flow field. A real CRH2 model is studied, with a leading car, a middle car and a trailing car included. Different running speeds and cross wind conditions are considered, and the approaches of unsteady Reynold-averaged Navier-Stokes (URANS) and detached eddy simulation (DES) are utilized, respectively. Results reveal that DES has better capability of capturing small eddies compared to URANS. However, for large eddies, the effects of two approaches are almost the same. In conditions without cross winds, two large vortex streets stretch from the train nose and interact strongly with each other in the wake zone. With the reinforcement of the ground, a complicated wake vortex system generates and becomes strengthened as the running speed increases. However, the locations of flow separations on the train surface and the separation mechanism keep unchanged. In conditions with cross winds, three large vortices develop along the leeward side of the train, among which the weakest one has no obvious influence on the wake flow while the other two stretch to the tail of the train and combine with the helical vortices in the train wake. Thus, optimization of the aerodynamic performance of the trailing car should be aiming at reducing the intensity of the wake vortex system