Quarterly Report of RTRI

PAPERS

Distortion of Compression Wave Propagating through Slab Track Tunnel with Side Branches

Takashi FUKUDA, Masanobu IIDA, Kaoru MURATA

2001 Volume 42 Issue 2 Pages 71-76
Published: 2001
Released on J-STAGE: July 11, 2007

DOIhttps://doi.org/10.2219/rtriqr.42.71

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When a high-speed train enters a tunnel, a compression wave is generated and propagates to the tunnel exit. At this moment, an impulsive pressure wave (micro-pressure wave) is emitted out of the exit. If its magnitude is large, it poses environmental problems. The magnitude of the micro-pressure wave is closely related to the pressure gradient of the compression wave arriving at the tunnel exit. Hence, to estimate the magnitude of the micro-pressure wave, it is required to investigate distortion of the compression wave propagating through tunnels. In this study, we investigate the distortion of the compression wave propagating through a slab track tunnel with short side branches by field measurement, numerical analysis and model experiment.

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Countermeasures for Reducing Pressure Variation due to Train Passage in Open Sections

Katsuhiro KIKUCHI, Yasuyuki TANAKA, Masanobu IIDA, Nobuaki YAMAUCHI, Y ...

2001 Volume 42 Issue 2 Pages 77-82
Published: 2001
Released on J-STAGE: July 11, 2007

DOIhttps://doi.org/10.2219/rtriqr.42.77

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As train velocity increases, aerodynamic problems become increasingly important for railways. In open sections, passing of a train nose, train tail and pantograph shield generate pressure variation along the wayside to cause environmental problems, such as rattling of window frames and shutters of houses near the railway. These phenomena are classified as infrasound. It is necessary to solve the problem of operating high-speed trains in the densely populated residential areas along the railways. This paper describes the results of recent researches conducted to develop effective countermeasures to reduce the pressure variation. We investigated the effect of the pressure barrier and train nose configuration as countermeasures.

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Pressure Waves Radiated Directly from Tunnel Portals at Train Entry or Exit

Masanobu IIDA, Yasuyuki TANAKA, Katsuhiro KIKUCHI, Takashi FUKUDA

2001 Volume 42 Issue 2 Pages 83-88
Published: 2001
Released on J-STAGE: July 11, 2007

DOIhttps://doi.org/10.2219/rtriqr.42.83

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It is well known that when a compression wave generated by a high-speed train entering a tunnel propagates through the tunnel and arrives at the far exit, a "micro-pressure wave" is radiated from the exit portal toward the surrounding area. In addition, the entering train generates impulsive pressure waves outside the tunnel, which are radiated directly from the entrance toward the neighboring area. A similar phenomenon also occurs when the train leaves the tunnel. We call the former a "tunnel entry wave", and the latter a "tunnel exit wave". Although the tunnel entry/exit wave is usually weaker than the micro-pressure wave, they could cause an environmental problem with increases in the train speed. In this paper, fundamental characteristics of the tunnel entry/exit wave are described based on the results of field measurement, model experiments and simple acoustic analysis.

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Unsteady Aerodynamic Force Acting on High Speed Trains in Tunnel

Masahiro SUZUKI

2001 Volume 42 Issue 2 Pages 89-93
Published: 2001
Released on J-STAGE: July 11, 2007

DOIhttps://doi.org/10.2219/rtriqr.42.89

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Vibration of high-speed trains increases in tunnels by aerodynamic force whose mechanism is unknown. To investigate this aerodynamic force, running tests and a numerical simulation were conducted. Analysis of the running test data showed that large-scale coherent structures exist in the space between the tunnel wall and the train. These flow structures develop from the head toward the 6th - 8th cars and become steady thereafter to the tail of the train set. Our computation revealed the mechanism of the generation of these flow structures. The flow becomes unstable by the difference in the velocity profile between the flow under the train and that on the side of the train. The resulted vortices are spread on the train side by the tunnel wall, and then the unsteady aerodynamic force is generated when the vortices pass.

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Wind Tunnel Tests to Reduce Aerodynamic Drag of Trains by Smoothing the Under-floor Construction

Atsushi IDO, Yoshihiko KONDO, Tsuyoshi MATSUMURA, Minoru SUZUKI, Tatsu ...

2001 Volume 42 Issue 2 Pages 94-97
Published: 2001
Released on J-STAGE: July 11, 2007

DOIhttps://doi.org/10.2219/rtriqr.42.94

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As a train runs at a higher speed, aerodynamic drag increases. On long train-sets such as Shinkansen trains, the aerodynamic drag is mainly generated by intermediate vehicles. In the previous researches, we proved that smoothing the under-floor construction reduces the aerodynamic drag. To investigate the mechanism of this effect, we performed wind tunnel tests with train models consisting of three vehicles (representing head, intermediate and tail vehicles) and measured the aerodynamic drag and the pressure distribution on the intermediate vehicle. Test results show that the reduced aerodynamic drag is mainly the effect of decreases in the pressure drag around bogies.

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Experimental Study on Aeroacoustic Noise Generated from Simplified Models on a Flat Base

Akio SAGAWA, Kiyoshi NAGAKURA

2001 Volume 42 Issue 2 Pages 98-103
Published: 2001
Released on J-STAGE: July 11, 2007

DOIhttps://doi.org/10.2219/rtriqr.42.98

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This report presents aeroacoustic characteristics of measured aerodynamic sounds radiated from simplified models on a flat base. The simplified models consist of a hemisphere, spheroid, half hemisphere and elongated hemisphere with an inserted half cylinder as an intermediate part of the hemisphere. An important purpose of these test models is to provide acoustic data which can be used to survey the aerodynamic noise from the upper parts of train front. An installation called the Maibara wind tunnel was used for experimental tests. As the results of analysis on the measured sound pressure from the test models, it is confirmed that a moving body which has an effectively smoothed and streamlined front shape can sufficiently decrease the aerodynamic noise generated from the upper parts even if its running speed reaches 350 km/h.

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Method of Analyzing the Wind Tunnel Test Data Measured with Directional Microphone Systems

Kiyoshi NAGAKURA

2001 Volume 42 Issue 2 Pages 104-109
Published: 2001
Released on J-STAGE: July 11, 2007

DOIhttps://doi.org/10.2219/rtriqr.42.104

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In order to clarify the characteristics of aerodynamic noise generated by high speed trains, wind tunnel tests are repeated and directional microphone systems, such as an acoustic mirror system, are generally used to localize the sources of aerodynamic noise. This paper explains the theoretical background of the principle of acoustic mirror and introduces an ellipsoidal shape chosen as the optimized shape of the mirror used for the Maibara large-scale low-noise wind tunnel. The characteristics of the acoustic mirror are verified experimentally and proved to be much better than those of old one which has a paraboloidal shape. Finally, the method to estimate the contributions of the localized noise sources to the far field noise level is proposed on the basis of the wind tunnel test data measured with directional microphone systems.

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Study on the Aeroacoustic Noise from Shinkansen with Mirror Image Models

Takehisa TAKAISHI, Yasuo ZENDA, Yasuhiro SHIMIZU

2001 Volume 42 Issue 2 Pages 110-114
Published: 2001
Released on J-STAGE: July 11, 2007

DOIhttps://doi.org/10.2219/rtriqr.42.110

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The effect of aeroacoustic noise on the sound level of Shinkansen train on the ground becomes increasingly important as the maximum speed increases. In order to simulate the effect of the ground that moves relative to the vehicle, a pair of mirror image models are tested at the Maibara Wind Tunnel which has an excellent low background noise level. Sound levels generated by several combinations of front shapes, bogie conditions and inter-car gaps are measured by a sound concentrating microphone with a paraboloidal reflector. Measurements of flow properties show that the noise is mainly generated by the vortices that are separated at the leading edge of the bogie section, travel leeward at the convective flow speed, and then impinge upon the trailing edge of the section.

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REVIEW

RTRI's Large-scale Low-noise Wind Tunnel and Wind Tunnel Tests

Tatsuo MAEDA, Yoshihiko KONDO

2001 Volume 42 Issue 2 Pages 65-70
Published: 2001
Released on J-STAGE: July 11, 2007

DOIhttps://doi.org/10.2219/rtriqr.42.65

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Four years have passed since the RTRI's Large-scale Low-noise Wind Tunnel was completed at Maibara in 1996. This wind tunnel was built to study aerodynamic noise and aerodynamic phenomena for high-speed trains and develop their reducing measures. This wind tunnel has two excellent features: one is the extremely low background noise which makes it possible to measure the noise generated from a model precisely and the other is a large and high-speed moving belt ground plane which enables the simulation of the flow between the model and the ground. This review reports the specifications of this wind tunnel and an outline of the tests performed over four years.

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