• Title/Summary/Keyword: Turbulent Noise

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A Study on Discrete Frequency Noise from a Symmetrical Airfoil in a Uniform Flow (에어포일 이산소음 특성에 관한 연구)

  • Kim, H.J.;Lee, S.B.;Fujisawa, N.
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2002.11b
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    • pp.646-651
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    • 2002
  • The flow field around a symmetrical airfoil in a uniform flow under the generation of noise was studied by experiments and numerical simulation. The experiments are conducted by visualizing the surface flow over the airfoil with a shear-sensitive liquid-crystal coating and by measuring the instantaneous velocity field around the trailing edge of the airfoil. The results indicate that the discrete frequency noise is generated when the separated laminar flow reattaches near the trailing edge of the pressure side and the turbulent boundary layer is formed over the suction side of the airfoil near the trailing edge. The periodic behavior of vortex formation was observed around the trailing edge and it persists further downstream in the wake. The frequency of the vortex formation in the wake was consistent with that of the discrete frequency noise.

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Trailing Edge Noise Modification in a Blade Cascade (익렬 날개 후단소음의 저감)

  • Son, J.M.;Kim, H.J.;Lee, S.B.;Cho, S.M.
    • The KSFM Journal of Fluid Machinery
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    • v.6 no.3 s.20
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    • pp.7-14
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    • 2003
  • It is addressed that the turbulent broadband sound power from a sirocco fan can be modeled by the trailing edge noise. The trailing edge noise is usually influenced by inflow turbulence, separation, and boundary layer thickness on the blade. The design parameters such as solidity (c/s) and stagger angle are specified to predict performance and noise level because the separation and slip velocity are strongly affected by them along with the flow coefficient. This paper reports the effects of the stagger angle upon the trailing edge noise for various trailing edge shapes. It is believed that the serrated trailing edge provides break-up mechanism for organized convecting vortices, thereby reduce the overall noise level for every case of stagger angle.

Experimental Study of Trailing Edge Shape of Forward Curved Blade upon Radiated Noise (원심 전향익 송풍기 날개 후단의 형상에 따른 소음 분석)

  • KIM, H.-J.;JUNG, K.-H.;LEE, C.-J.;LEE, S.
    • 유체기계공업학회:학술대회논문집
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    • 2000.12a
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    • pp.137-142
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    • 2000
  • The turbulent broadband sound power from a forward curved bladed fan can be modeled by the trailing edge noise. The trailing edge noise is usually influenced by inflow turbulence, separation, and boundary layer on the blade. This paper reports the effects of the solidity (C/s) and the stagger angles upon the trailing edge noise with respect to the trailing edge shapes of circular-arc cambered blade of multi-bladed fan, and discusses the major physical mechanism of reduced noise lot the circular trailing-edged case.

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Analysis of Trail-Edge Noise from Sirocco Fans (시로코 홴 날개후단 소음예측)

  • Kim, Kyoung-Ho;Lee, Seung-Bae;Kim, Ji-Sung;Kwon, Yang-Hoon
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2000.06a
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    • pp.396-401
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    • 2000
  • It is addressed that the turbulent broadband sound power from a sirocco fan can be modeled by the trailing edge noise. The trailing edge noise is usually influenced by inflow turbulence, separation, and boundary layer on the blade. The design parameters such as solidity(c/s) and stagger angle are specified to predict performance and noise level because the separation and slip velocity are strongly affected by them along with the flow coefficient. This paper reports the effects of the solidity and the stagger angle upon the trailing edge noise from the circular arc-shaped blade of sirocco fan.

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The aero-acoustic noise reduction based on biomimetics : A case study (생체모방공학을 이용한 공력 소음 저감 기초 연구)

  • Han, Jae-H.;Kim, Tae-M.;Kim, Jung-S.
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2011.04a
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    • pp.144-151
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    • 2011
  • Recent years have witnessed speed up of moving vehicles such as high-speed of trains. Increase in speed entails concomitant increase in turbulent air flow which contributes toward aerodynamic noise. The proposed method for aerodynamic noise reduction is based on a biomimetic design of owl feather. The five morphological parameters of the owl feather is extracted from close observation, and simulation cases are constructed by applying design of experiments methodology. Swirling strength for each case is obtained through steady-state CFD analysis, and key morphological parameters that affect the turbulence are identified. Large eddy simulations (LES) are then performed on selected cases to predict the air turbulence. Different cases show varying vorticity distribution levels which is expected to lead to varying aerodynamic noise levels.

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A Study of The Tilt-up Sunroof Wind Noise (자동차 선루프 틸트업 바람소리 연구)

  • Lee, Myunghan;Cho, Munhwan;Ih, Kangduck;Choi, Euisung
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2013.04a
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    • pp.788-792
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    • 2013
  • There are three significant noises from the sunroof while driving. Among them, sunroof tilt-up noise has mainly high-frequency characteristics in the side and rear openings of sunroof. Because of complex structures to operate sunroof, significant flow disturbance makes strong turbulent noise. In this study, sunroof tilt-up noise was predicted by using numerical simulation code and the results were compared with experimental data.

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Prediction Method for Trailing-edge Serrated Wind Turbine Noise (풍력발전기 톱니형 뒷전 블레이드 소음 예측 기법)

  • Han, Dongyeon;Choi, Jihoon;Lee, Soogab
    • New & Renewable Energy
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    • v.16 no.2
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    • pp.1-13
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    • 2020
  • The reduction of noise from wind turbines has been studied using various methods. Some examples include controlling wind turbine blades, designing low-noise-emitting wind turbine blades, and using trailing-edge serrations. Among these methods, serration is considered an effective noise reduction method. Various studies have aimed to understand the effects of trailing-edge serration parameters. Most studies, however, have focused on fixed-wing concepts, and few have analyzed noise reduction or developed a prediction method for rotor-type blades. Herein, a noise prediction method, composed of two noise prediction methods for a wind turbine with trailing-edge serrations, is proposed. From the flow information obtained by an in-house program (WINFAS), the noise from non-serrated blades is calculated by turbulent ingestion noise and airfoil self-noise prediction methods. The degree of noise reduction caused by the trailing-edge serrations is predicted in the frequency domain by Lyu's method. The amount of noise reduction is subtracted from the predicted result of the non-serrated blade and the total reduction of the noise from the rotor blades is calculated.

Effect of Nozzle Lip Thickness on the Characteristics of Supersonic Jet Noise (노즐립 두께가 초음속 제트의 소음특성에 미치는 영향)

  • Kweon, Yong-Hun;Aoki, Toshiyuki;Kim, Heuy-Dong
    • Proceedings of the KSME Conference
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    • 2003.11a
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    • pp.520-525
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    • 2003
  • Supersonic jet issuing from a nozzle invariably cause high-frequency noises. These consist of three principal components ; the turbulent mixing noise, the broadband shock-associated noise, and the screech tone. In present study, it was experimentally investigated to the effect of nozzle lip thickness on the characteristics of supersonic jet noise. The convergent-divergent nozzle of a design Mach number 2.0 was used in experiment. With three different nozzle-lip thicknesses, the jet pressure ratio was varied in the range between 2.0 and 12.0. Acoustic measurements were conducted by microphones in an anechoic room, and the major structures of the supersonic jets were visualized by a Schlieren optical system to investigate the effect of nozzle lip thickness. The measured results show that the characteristics of supersonic jet noise, such as overall sound pressure level (OASPL) and screech frequency, strongly depend upon the thickness of nozzle-lip.

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Statistical study of turbulence from polarized synchrotron emission

  • Lee, Hyeseung;Cho, Chungyeon;Lazarian, Alexandre
    • The Bulletin of The Korean Astronomical Society
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    • v.42 no.1
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    • pp.56.1-56.1
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    • 2017
  • When turbulent motions perturb magnetic field lines and produce magnetic fluctuations, the perturbations leave imprints of turbulence statistics on magnetic field. Observation of synchrotron radiation is one of the easiest ways to study turbulent magnetic field. Therefore, we study statistical properties of synchrotron polarization emitted from media with magnetohydrodynamic (MHD) turbulence, using both synthetic and MHD turbulence simulation data. First, we obtain the spatial spectrum and its derivative with respect to wavelength of synchrotron polarization arising from both synchrotron radiation and Faraday rotation. The study of spatial spectrum shows how the spectrum is affected by Faraday rotation and how we can recover the statistics of underlying turbulent magnetic field as well as turbulent density of electrons from interferometric observations that incorporate the effects of noise and finite telescopic beam size. Second, we study quadrupole ratio to quantitatively describe the degree of anisotropy introduced by magnetic field in the presence of MHD turbulence. We consider the case that the synchrotron emission and Faraday rotation are spatially separated, as well as the situation that the sources of the synchrotron radiation and thermal electrons causing Faraday rotation exist in the same region. In this study, we demonstrate that the spectrum and quadrupole ratio of synchrotron polarization can be very informative tools to get detailed information about the statistical properties of MHD turbulence from radio observations of diffuse synchrotron polarization.

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Large Eddy Simulation of Turbulent Flows over Backward-facing Steps (후향 계단에서 난류 유동에 대한 대와동모사)

  • Hwang, Cheol-Hong;Kum, Sung-Min
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.10 no.3
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    • pp.507-514
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    • 2009
  • Large eddy simulation code was developed to predict the turbulent flows over backward-facing steps including a recirculating flow phenomena. Localized dynamic ksgs-equation model was employed as a LES subgrid model and the LES solver was implemented on parallel computer consisting of 16 processors to reduce computational costs. The results of laminar flow showed qualitative and quantitative agreements between current simulations and experimental results availablein literatures. The simulation of the turbulent flows also yielded reasonable results. From these results, it can be expected that developed LES code will be very useful to analyze the combustion in stabilities and noise of a practical combustor in the future.