• Title, Summary, Keyword: Aerodynamic Noise

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Numerical Study on Discrete and Broadband Noise Generated from Horizontal Axis Wind Turbine Blade (수평축 풍력터빈 블레이드의 이산소음과 광역소음의 수치해석)

  • Ryu, Ki-Wahn;Yu, Byung-Min
    • 한국신재생에너지학회:학술대회논문집
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    • pp.315-318
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    • 2008
  • Numerical calculation for the 1MW class horizontal axis wind turbine blade has been carried out to estimate the magnitude between discrete noise and random noise. Farassat formula 1A was adopted to get the discrete noise signal, and blade element momentum theory was used to obtain the distribution of the aerodynamic data along the blade span. Fukano's approach was also adopted to calculate the unsteady aerodynamic random noise due to the Karman vortex generation at the trailing edge of the wind turbine blade. From the noise prediction for the 1MW class horizontal axis wind turbine, the frequency band of the discrete noise lies in the infrasound region, and that of the random noise lies in the audible band region.

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Aerodynamic Noise Prediction of Subsonic Rotors

  • Lee, Jeong-Han;Lee, Soo-Gab
    • The Journal of the Acoustical Society of Korea
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    • v.16 no.1E
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    • pp.29-34
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    • 1997
  • Numerical prediction of aerodynamic noise radiated by subsonic rotors are carried out. A computer program has been developed which incorporates both the discrete frequency noise as well as the broadband noise arising from the ingestion of turbulence. Acoustic analogy is used in conjunction with Homicz's formulation of turbulence ingestion noise. Formulation 1A of Farassat is used to enhance the numerical analysis performance of Ffowcs-Williams Hawkings equation by eliminating the numericla time differentiation. Homicz's trubulence ingestion noise prediction technique is used to understand the characteristics of broadband noise radiated by isotropic trubulence in gestion. Numerical predictions are carried out for a number of rotor configurations and compared with experimental data. Monopole consideration of transonic rotor agrees well with both the experimental data and the linear theory. Noise radiation characteristics of rotor at lifting hover are investigated utilizing simple blade loading obtained by thin wing section theory. By incorporating discrete noise prediction of steady loading with broadband spectrum, much better agreement with experimental data is obtained in the low frequency region. The contributions from different noise mechanisms can also be analyzed through this method.

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A Study on the Aerodynamic Noise of a Supersonic Exhaust Nozzle of Perforated Tube (다공관형 초음속 배기노즐의 공력소음에 관한 연구)

  • 이동훈
    • Journal of KSNVE
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    • v.9 no.1
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    • pp.113-120
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    • 1999
  • A perforated tube nozzle as an exhaust noise suppressor of a high-speed civil transport(HSCT) is proposed. The experimental results for the near and far field sound. the visualization of jet structures and the static pressure distributions in the jet passing through a perforated tube are presented and discussed in comparison with those for a simple tube. It is shown that the perforated tube has an excellent performance to greatly reduce the shock-associated noise and that also the turbulent mixing noise is reduced in the range of a limited jet pressure ratio. This considerable noise reduction is due to the pressure relief caused by the through-flow through the perforated holes. Such a pressure relief results in the transformation of normal shock waves into weak Mach waves of X -type and increases the thrust force of the perforated tube nozzle.

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Development of Hybrid Method for the Prediction of Internal Flow-induced Noise and Its Application to Throttle Valve Noise in an Automotive Engine

  • Cheong, Cheol-Ung;Kim, Sung-Tae;Kim, Jae-Heon;Lee, Soo-Gab
    • The Journal of the Acoustical Society of Korea
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    • v.22 no.4E
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    • pp.183-196
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    • 2003
  • General algorithm is developed for the prediction of internal flow-induced noise. This algorithm is based on the integral formula derived by using the General Green Function, Lighthill's acoustic analogy and Curl's extension of Lighthill's. Novel approach of this algorithm is that the integral formula is so arranged as to predict frequency-domain acoustic signal at any location in a duct by using unsteady flow data in space and time, which can be provided by the Computational Fluid Dynamics Techniques. This semi-analytic model is applied to the prediction of internal aerodynamic noise from a throttle valve in an automotive engine. The predicted noise levels from the throttle valve are compared with actual measurements. This illustrative computation shows that the current method penn its generalized predictions of flow noise generated by bluff bodies and turbulence in flow ducts.

Identifications and Reductions of Aerodynamic Noise Sources in High Speed Rotating CD-Rom Drive (고속으로 회전하는 CD-Rom 드라이브의 공력 소음원 규명 및 소음 저감)

  • Heo, Dae-Nyoung;Kim, Yong-Seok;Han, Seung-Jin;Kim, Young-Chan;Lee, Duck-Joo
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.771-776
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    • 2000
  • Major noise source in high speed rotating CD-Rom drives arises due to the high-speed airflow produced from the upper and lower surfaces on the rotating disk. The present paper deals with the experimental approach how to identify the noise source based on the fundamental principles of aeroacoustics and to propose a reduction method of the noise source. Experimental studies were carried out in the anechoic wind tunnel with various design modifications, such as tray geometry and window size, to identify and reduce the major aerodynamic noise source and significant reductions of the noise source were obtained.

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A Study on the Effect of Mud-flap on the Cabin Noise in KTX (고속열차의 객실 소음에 미치는 머드플랩의 영향에 관한 연구)

  • Choi, Seong-Hun;Chung, In-Soo;Seo, Sung-Il
    • Journal of the Korean Society for Railway
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    • v.9 no.5
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    • pp.550-554
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    • 2006
  • In the early stage of operation of KTX, passengers complained of the excessive cabin noise as the passes the tunnel. The noise is caused partly by wheel-rail contact and partly by airflow around the carbody. In this study, to reduce the cabin noise, the effect of the mud-flaps located between the cars is investigated. A series of tests was conducted to clarify the influences of the type and length of mud-flap, and train speed on the cabin noise. The optimum length of mud-flap was found. The shedding vortices around the mud-flap is thought to be the cause of the aerodynamic noise. Strouhal number and the resonant shedding frequency around the mud-flap correlated well with the cabin noise level.

Analysis on Performance of Axial Flow Fan for Outdoor Unit of Air-conditioner: Noise Characteristics (에어컨 실외기용 축류홴의 성능에 관한 연구: 소음 특성)

  • Kim, Yong-Hwan;Lee, Jang-Ho
    • The KSFM Journal of Fluid Machinery
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    • v.13 no.5
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    • pp.29-34
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    • 2010
  • In this paper, aerodynamic noise of axial flow fans for outdoor unit of air-conditioner was analyzed by both experiment and numerical simulation. The three-dimensional incompressible turbulent flow was predicted by the commercial computational fluid dynamics code SC/Tetra, while the aeroacoustic noise of an axial flow fan was predicted by FlowNoise. Computations and experiments were performed with two types of axial flow fans, in which very different noise source distributions were presented. The results obtained from this study are expected to show the way to reduce the noise of axial flow fans in industrial applications.

Prediction of Aeroacoustics Noise of Pantograph via Low Speed Wind Tunnel Test and Flow Simulation (저속풍동실험 및 유동해석을 통한 고속전철 판토그라프의 유동소음 해석)

  • 조운기;이종수
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.1207-1214
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    • 2001
  • The paper deals with the computational approach in analysis and design of pantograph panhead strips of high-speed railway in aerodynamic and aeroacoustic concerns. Pantograph is an equipment such that the electric power is supplied from catenary system to train. Due to the nature of complexity in high-speed fluid flow, turbulence and downstream vortices result in the instability in the aerodynamic contact between panhead strips and catenary system, and consequently generate the considerable levels of flow-induced sound. In this paper, based on the preceding low speed wind-tunnel test and simulations, the aerodynamic and aeroacoustic characteristics in low speed are analyzed.

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Flow Field Analysis inside Intake Nozzles of a Household Vacuum Cleaner

  • Daichin Daichin;Lee Sang Joon
    • Proceedings of the KSME Conference
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    • pp.733-736
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    • 2002
  • The inside configuration of intake nozzle of vacuum cleaner greatly affects the dust-collection efficiency and acoustic-noise effect generated from flow separation Interaction between high-speed flow and internal structure. In order to improve the performance of the vacuum cleaner, flow fields inside the intake nozzles were investigated using flow visualization and FIV (Particle Image Vetocimetry) technique. The measurement to aerodynamic power, suction efficiency and noise level were also carried out. Valuable information was obtained from the experiments, revealing how to modify the intake nozzle. In this paper, the results of visualization, velocity distribution of flow fields, aerodynamic power, suction efficiency and noise level are discussed.

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