TED-AJ03-300 AERODYNAMIC SOUND GENERATED BY INTERACTION BETWEEN VORTICES AND A BODY
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概要
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Recently, numerical calculations are regarded useful to design an air-conditioner, in which the prediction of temperature distribution at an air outlet nozzle is the most important factor. To predict temperature distribution exactly, it is essential to estimate the velocity distribution. However, since internal flow of an actual air-conditioner becomes a complex turbulent flow field with separation and vorticity generation, the aerodynamic sound generated by flow impingement and interaction between vortices and the solid boundary is a key issue. Furthermore, the noise reduction of the fans widely used in air-conditioners, is a technical problem to be resolved. Thanks to the progress of the recent Computational Fluid Dynamics, the performance such as the discharge flow rate and the mean temperature of an air-conditioner predictable before producing a prototype. However, noise prediction is still extremely difficult, so one must inevitably measure the actual noise generated by an actual product before mass-production. Thus far, technical improvements based on know-how from past experience have generally been adopted to reduce the air-conditioner noise for each product using the actual product at considerable cost and time. However, this approach is reaching its limits. Therefore, for the design of an air-conditioner, the prediction of fluid noise is as important as the accurate prediction of velocity and temperature distributions. Therefore, a comprehensive thermal fluid simulation tool is required. In this study, our final objective is to develop a simulation tool for the accurate prediction of temperature distribution and noise reduction. The purpose of this study is to obtain knowledge of the prediction of fluid noise by means of practical numerical analysis. Research on the prediction of the fluid noise is still only at the basic-model stage, and only a few reports have been published. Also, there are few examples from past research which explain the fluid noise in detail using the sound analytic technique, and to our knowledge they make no reference to the position of a sound source and the occurrence mechanism. Aerodynamic sound, which is the main factor in the noise of an air-conditioner and generated by interaction between vortices and an interfering body, has been the aim of our experimental study. A two-dimensional circular cylinder is used for the formation of vortices, and a two-dimensional wing is used as the body to provide interference on the downstream side of the cylinder. A sound with a remarkable peak has been confirmed from frequency analysis of the noise generated in this situation. Also, it is found that the noise originates in the flow-induced vortex because the peak frequency noise changes in proportion to the mainstream speed. Next, it is confirmed that the sound source is somewhere near the trailing edge of the wing, which provides the interference, as a result of analyzing this peak acoustic frequency by the acoustic intensity measurement method. Furthermore, from visualization of the flow near the sound source by a high-speed video camera, in order to determine the relationship with the sound, it is clarified that the noise is generated when the vortex developing from the cylinder to form the secondary vortex due to the vortex/wing interference breaks down near the trailing edge of the wing.[figure]
- 一般社団法人日本機械学会の論文
著者
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Miyata Manabu
Air-conditioning R & D Dept. 3 Denso Corporation
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NAGANO Yasutaka
Department of Mechanical Engineering, Nagoya Institute of Technology
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Nagano Yasutaka
Department Of Environmental Technology And Urban Planning Graduate School Of Engineering Nagoya Inst
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