Studies of Two Aerodynamic Effects on High-Speed Trains : Crosswind Stability and Discomforting Car Body Vibrations Inside Tunnels

QC 2011011

Large Eddy Simulations of the Flow Around High-Speed Trains Cruising Inside Tunnels

Stability and ride comfort of high-speed rolling stock are, for reasons of external aerodynamics, dependent on the external design in conjunction with properties of the vehicle dynamics and the design of the infrastructure, herein referring to the confining tunnel walls. It is a fact that some Japanese high-speed trains are quite prone to tail vehicle vibrations only inside tunnels, while (to the authors knowledge) other nations comparable train systems are not. In this context the current work describes our results of external aerodynamics, calculated with large eddy simulations, about two simplified train models inside two double track tunnels with comparable blockage ratio. These models are based on the German Inter-City Express 2 and the Japanese Series 300 Shinkansen trains. The focal points of this study are the origin of unsteady aerodynamic tail forces, their spectral characteristics and the impact of spontaneously emerging coherent flow structures adjacent to the trains surfaces. Full scale tests of the above trains have shown that only the Shinkansen train is subjected to a reduced ride comfort inside tunnels, with a quite obvious lateral vibration at about 2 Hz at top speed (300 km/h). Our unsteady flow calculations have successfully predicted the more detrimental lateral aerodynamic forces. In addition, a spectral analysis of the unsteady side force resulted in a quite prominent frequency at the Strouhal number of 0.09 (based on the speed and height of the train), which correlates well with the Japanese full scale tests

Large Eddy Simulations of the Flow Around High-Speed Trains Cruising Inside Tunnels

Stability and ride comfort of high-speed rolling stock are, for reasons of external aerodynamics, dependent on the external design in conjunction with properties of the vehicle dynamics and the design of the infrastructure, herein referring to the confining tunnel walls. It is a fact that some Japanese high-speed trains are quite prone to tail vehicle vibrations only inside tunnels, while (to the authors knowledge) other nations comparable train systems are not. In this context the current work describes our results of external aerodynamics, calculated with large eddy simulations, about two simplified train models inside two double track tunnels with comparable blockage ratio. These models are based on the German Inter-City Express 2 and the Japanese Series 300 Shinkansen trains. The focal points of this study are the origin of unsteady aerodynamic tail forces, their spectral characteristics and the impact of spontaneously emerging coherent flow structures adjacent to the trains surfaces. Full scale tests of the above trains have shown that only the Shinkansen train is subjected to a reduced ride comfort inside tunnels, with a quite obvious lateral vibration at about 2 Hz at top speed (300 km/h). Our unsteady flow calculations have successfully predicted the more detrimental lateral aerodynamic forces. In addition, a spectral analysis of the unsteady side force resulted in a quite prominent frequency at the Strouhal number of 0.09 (based on the speed and height of the train), which correlates well with the Japanese full scale tests

Large Eddy Simulations of a typical European high-speed train inside tunnels

This article presents our results of external aerodynamics, obtained with Large Eddy Simulations (LES), about a typical European passenger-stock inside tunnels. The focal points are the aerodynamic forces and their typical frequencies applied to the tail. Two train lengths and three tunnels are employed in the study to model the conditions of double and single-track bores. Owing to the relatively high numerical cost associated with LES for external train aerodynamics we could only afford sufficient spatial grid resolution on our shortest train. The flow simulations confirm the existence of coherent structures alongside the body that give rise to continuously propagating pressure disturbances. These disturbances with a relatively small amplitude and high spatial frequency cannot affect the ride comfort. Still, they are found to influence the flow separation about the tail, which is regarded as one of the candidate mechanisms to impair the ride comfort and running stability

Time-Dependent Simulations for the Directional Stability of High Speed Trains Under the Influence of Cross Winds or Cruising Inside Tunnels

Large eddy simulation (LES) technique is used to study safety and comfort issues of cross-wind stability and lateral vehicle vibrations in double-track tunnels. A simplified train model is used to study flows at yaw angles of 90 and 35 degrees of the cross wind and Reynolds numbers of 300 000 and 370 000, respectively. LES results are compared with the experimental data and good agreement was found. For the LES investigation of lateral vibrations in tunnel, two high-speed trains are used, the German ICE2 and the Japanese Shinkansen S300. It is found that the lateral oscillations of the Shinkansen train originate from the shape of the rear end. Besides, the small vortices formed at the front of the train, on the center side of the tunnel, are found to govern the separation at the rear of the Shinkansen train. The frequency of the lateral oscillations of the Shinkansen train in LES is St=0.09 compared to St=0.1 measured at full scale tests. In the same time no dominant frequency is found on the ICE2 train

Time-Dependent Simulations for the Directional Stability of High Speed Trains Under the Influence of Cross Winds or Cruising Inside Tunnels

Large eddy simulation (LES) technique is used to study safety and comfort issues of cross-wind stability and lateral vehicle vibrations in double-track tunnels. A simplified train model is used to study flows at yaw angles of 90 and 35 degrees of the cross wind and Reynolds numbers of 300 000 and 370 000, respectively. LES results are compared with the experimental data and good agreement was found. For the LES investigation of lateral vibrations in tunnel, two high-speed trains are used, the German ICE2 and the Japanese Shinkansen S300. It is found that the lateral oscillations of the Shinkansen train originate from the shape of the rear end. Besides, the small vortices formed at the front of the train, on the center side of the tunnel, are found to govern the separation at the rear of the Shinkansen train. The frequency of the lateral oscillations of the Shinkansen train in LES is St=0.09 compared to St=0.1 measured at full scale tests. In the same time no dominant frequency is found on the ICE2 train

Vehicle dynamics of a high-speed passenger car due to aerodynamics inside tunnels

High train speeds inside narrow double-track tunnels using light car bodies can reduce the ride comfort of trains as a consequence of the unsteadiness of the aerodynamics. This fact was substantiated in Japan with the introduction of the series 300 Shinkansen trains more than a decade ago, where the train speed is very high also in relatively narrow tunnels on the Sanyo line. The current work considers the resulting effects of vehicle dynamics and ride comfort with multi-body dynamics using a model of the end car of the German high-speed train ICE 2. The present efforts are different from traditional vehicle dynamic studies, where disturbances are introduced through the track only. Here disturbances are also applied to the car body, which conventional suspension systems are not designed to cope with. Vehicle dynamic implications of unsteady aerodynamic loads from a previous study are examined. These loads were obtained with large eddy simulations based on the geometry of the ICE 2 and Shinkansen 300 trains. A sensitivity study of some relevant vehicle parameters is carried out with frequency response analysis (FRA) and time domain simulations. A comparison of these two approaches shows that results which are obtained with the much swifter FRA technique are accurate also for sizable unsteady aerodynamic loads. FRA is, therefore, shown to be a useful tool to predict ride comfort in the current context. The car body mass is found to be a key parameter for car body vibrations, where loads are applied directly to the car body. For the current vehicle model, a mass reduction of the car body is predicted to be most momentous in the vicinity of 2 Hz