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The aerodynamic characteristics of a conventional line pantograph in a crosswind were investigated by conducting large-eddy simulations (LESs). In a previous study, wind tunnel tests using a full-scale pantograph were performed at various attack angles of the crosswind to understand the lift force characteristics of a pantograph in crosswind conditions. These experiments revealed that the lift force increases significantly when the yaw angle is set to 56°; however, the mechanism of increment of the lift force has not been clarified. Therefore, the flow fields around the pantograph head were investigated. It was found that there are two main mechanisms: one is a stationary large-scale vortex generated on the upper surface of the pantograph head, and the other is a pressure increment on the lower surface of the pantograph head. In addition, LESs were conducted using modified pantograph head shapes to investigate methods for reducing the lift force of the pantograph head using the mechanisms above. Two changes to the pantograph head shape were considered: a diagonal cut on the lower surface of the pantograph head and opening sections on the upper and lower surfaces of the pantograph head. The former shape generates a negative pressure area under the pantograph head, while the latter attenuates the large-scale vortex on the upper surface of the pantograph head. Thus, they achieve lift reduction by different mechanisms and can be used together. The lift reduction rate reaches approximately 60% when both methods are used together, indicating that this is an effective lift force reduction method.

In this study, a large-eddy simulation (LES) is conducted to investigate meandering airflows generated throughout the underbody of a real-shaped train model in open air. In our previous study, this was shown by an LES of airflows around a simplified train model. The shape of the underbody affects the flow. However, thus far, no systematic analyses that consider bogies have been conducted. Our experimental results qualitatively reproduced the power spectra of lateral velocity fluctuations in the underbody obtained using a 1:8.4-scale train model on a moving belt in a wind tunnel. Results on the effects of various bogie shapes suggested that the meandering flow was primarily affected by the time-averaged profile of streamwise velocity. Thus, the effects of the bogie shape on airflow are considerable. Comparing bogie shapes with and without a side cover, that without a side cover generated meandering airflow with a slightly smaller peak frequency than that with a side cover, and a completely smooth bogie generated no meandering airflows. It was confirmed that this LES was useful as a technical tool to develop measures to reduce meandering airflows around high-speed trains.

To clarify the mechanisms underlying airflow-induced vibrations of high-speed trains running through tunnels, large-eddy simulation of a large-scale flow structure around a simplified 6-car train model was conducted. Since actual trains run on one of the double track lines, the position of the train model was made to deviate from the tunnel center and hence the gap between one of the sides of the train and the tunnel wall is narrower than that of the other side. A train running in the open air was also calculated for comparison. The results of this study shed light on the generation mechanism of the pressure fluctuations acting on the side of high-speed trains as follows. Firstly, in the open air, the air velocity in the space between the underbody and the ground gradually decreases from the head toward the tail of the train. Thus, the air velocity is slower than that on both sides of the train, which generates shear flows near the bottom edges of both sides of the train. The shear flows cause large Karman vortex-like vortices (staggered Karman vortex street), which in turn lead to a meandering airflow beneath the underbody of the train. Secondly, in the tunnel, the air velocity not only in the gap between the underbody and the ground but also in the narrower gap between the side of the train and the tunnel wall gradually decreases from the head toward the tail of the train. In the same mechanism as the open air, a meandering airflow is generated throughout the side and underbody of the train and causes pressure fluctuations along the side of the train. Finally, it is demonstrated that the wavelength of pressure fluctuations along the side of the actual train can be estimated from the present LES results.

Under the existing method based on a detailed equation for evaluating the wind speed that can cause a vehicle to overturn, it is assumed that the crosswind blows the vehicle at the same wind speed uniformly over the entire length of the vehicle body along the track. However, taking into consideration the actual wind state, there is a wind speed distribution over the length of the vehicle body and there is a high possibility that the crosswind does not blow at the same wind speed over the entire length of the vehicle body. Therefore, if the wind speed distribution is considered, it becomes possible to evaluate the critical wind speed in more detail. In previous research, an evaluation formula of aerodynamic force in consideration of the wind speed distribution has been proposed with the natural wind direction assumed to be 90 degrees. On the other hand, the calculation of the wind speed that can cause a vehicle to overturn requires extending the evaluation formula so as to be applicable to the other natural wind directions. In this study we proposed, extending the existing evaluation formula, a method of calculating the critical wind speed in consideration of the spatial fluctuation of wind speed. We also evaluated the critical wind speed for the combination of the vehicle and the track constructions with the proposed method. In addition, we also evaluated the critical wind speed in accordance with changes in the height of the center of the car body from the ground and the roughness length. As a result of the evaluation, we confirmed that the critical wind speed increases by up to 1.4m/s, provided that the vehicles and railway structures are those assumed in this study.

A pantograph mounted on a high-speed train roof is exposed to high-speed air flow while traveling, and lift force is generated in the pantograph. To ensure high current collecting performance of the pantograph, it is important to appropriately adjust the lift force generated in the pantograph. The flow velocity along the roof of a train has a significant influence on the lift force. In this study, we proposed a simple calculation method that enabled us to easily calculate the flow on the train roof in a tunnel using a personal computer. To validate the effectiveness of the proposed method, model experiments were carried out and calculation and experimental results were compared. Furthermore, the influence of hydraulic friction coefficients on train roof flow velocity was examined using the proposed method, which was not time consuming.