Aerodynamic Sound and Flow Field Generated from Combinational Inclined Tapered Cylinder

Kohei Sato, Ryutaro Machida, Toshiyuki Aoki

Graduate School of Engineering Sources, Kyushu University, Kasuga, Japan.

DOI: 10.4236/ojfd.2012.24A025                

Abstract

This study deals with the aerodynamic sound, especially the Aeolian tone. One of the problems with the aerodynamic sound, noise reduction along a railway line is significant engineering issue for further speed-up of a high-speed train. In particular, a pantograph is one of the main aerodynamic noise sources of a high-speed train. As one of the methods for the aerodynamic noise reduction, this study proposes the tapered cylinder by a pantograph. In this paper, the aerodynamic sound and the wake flow of the combinational inclined circular cylinder and tapered cylinder are experimentally and numerically investigated in knuckle upstream and knuckle downstream. Also, we suggest that the surface of grooves such as wood grain interacts with the aerodynamic sound generated from the model. Here, it is considered that the comparison of aerodynamic sound between the model with grooves and without grooves. Consequently, reduction of the maximum aerodynamic sound is possible for the tapered cylinder in the case of knuckle downstream. Furthermore, the noise reduction method is effective that the model surface with grooves such as wood grain.

Keywords

Aerodynamic Sound; Aeolian Tone; Inclined Tapered Cylinder; Flow Field

1. Introduction

This study deals with the aerodynamic sound, especially the Aeolian tone. One of the problems with the aerodynamic sound, noise reduction along a railway line is significant engineering issue for further speed-up of a highspeed train. The way of the noise reduction has strongly been required. As far as the present high-speed train is concerned, the contribution of aerodynamic sound is dominant when comparing with other kinds of the noises, such as rolling noise, concrete structure noise and so on. In particular, a pantograph is one of the main aerodynamic noise sources of a high-speed train. Therefore, researcher who develops the low noise pantograph has been continued [1-4]. The low noise pantograph is constructed to a configuration as simple as possible to reduce noise sources. The form of a pantograph should be aerodynamically-smoothed to reduce the aerodynamic sound.

The Aeolian tone generated from a circular cylinder has been widely studied by many researchers. In general, a straight circular cylinder generates narrowband peak noise. According to other researchers [5,6], the tapered cylinder generates lower level of Aeolian tone than the circular cylinder. Furthermore, when the side of the large diameter of the tapered cylinder is set downstream at the inclined from −40 to 40 degrees, the Aeolian tone becomes large compared with the zero degrees [7,8]. It is clear that the Aeolian tone is governed with the flow fluctuation in the wake.

As one of the methods for aerodynamic noise reduction, this study proposes the tapered cylinder by a pantograph as shown in Figure 1. Thus it is important that the characteristics of the combinational inclined tapered cylinder should be made clear.

In this paper, we experimentally and numerically investigate the aerodynamic sound and the wake flow of the combinational inclined tapered cylinder and circular cylinder in knuckle upstream and knuckle downstream.

2. Experimental Procedure

2.1. Test Models

Figure 2 shows the experimental models. There are three types of the models, that is, 1) Type A for combinational inclined circular cylinder (diameter: D = 12 mm); 2) Type B for combinational inclined tapered cylinder (increasing diameter to knuckle); and 3) Type C for combinational inclined tapered cylinder (increasing diameter from knuckle). The minimum diameter of each model is 12 mm. When diameter is 12 mm, it is enough to satisfy the aspect ratio for Aeolian tone generation. Here, the aspect ratio is 15 which calculated from the nozzle height and the model diameter. The tapered angle is 5 degrees, and knuckle angle is 60 degrees. The material of the

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	T. Sueki, M. Ikeda and T. Takaishi, “The Aerodynamic Noise Reduction by Porous Materials and Application to a Current Collector,” RTRI Report, Vol. 22, No. 5, 2008, pp. 26-31.
[2]	Y. Ijichi, T. Odo, N. Kondoh and T. Aoki, “Sound Characteristic of Aerodynamic Noise Generated from Pantograph on a High-Speed Train,” Journal of JSME, Vol. 61, No. 85-2, 2008, pp. 19-20.
[3]	M. Ikeda and T. Mitsumoji, “Method to Evaluate Structure of Low-Frequency Aerodynamic Noise Source Generated by Shinkansen Pantograph,” RTRI Report, Vol. 21, No. 12, 2007, pp. 47-52.
[4]	K. Shibata, M. Hirai, T. Hariyama and Y. Sasaki, “Development of Low Noise Pantograph Adopted to the Superexpress Hayate,” Mitsubishi Heavy Industries Technical Review, Vol. 40, No. 3, 2003, pp. 154-157.
[5]	K. Saito, H. Fujita and Y. Suzuki, “Experimental Study of the Characteristics of the Aeolian Tone and the Wake structures Generated from Tapered Circular Cylinders,” Journal of JSME Fluid Engineering Conference 2010, Vol. 1006, No. 88, 2010, pp. 271-272.
[6]	J. Fukutomi, Y. Nakase and M. Takikawa, “Vortex Wake from Tapered and Stepped Circular Cylinders in a Uniform Flow,” Journal of JSME, Vol. 59, No. 92, 1993, pp. 684-690.
[7]	T. Tsuchida, H. Hayashi, Y. Kodama, T. Fukano and S. Sasaki, “Relationship between Aeolian Tone and Wake of Inclined Tapered Cylinder,” Journal of JSME Environment Engineering Symposium 2006, Vol. 112, No. 16, 2006, pp. 65-68.
[8]	Y. Haramoto, K. Matsuzaki, M. Munekata and H. Ohba, “An Experiment and Numerical Simulation of Aerodynamic Sound Generated from Inclined Circular Cylinder,” Journal of the Acoustical Society of Japan, Vol. 301, No. 58, 2002, pp. 282-288.