• Title/Summary/Keyword: Turbulent Noise

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Characteristics of Flow-Induced Noise around a Sphere (구 주위의 유동으로 인해 발생하는 유동 소음의 특성)

  • Yun, Gi-Woong;Choi, Hae-Cheon
    • Proceedings of the KSME Conference
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    • 2003.11a
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    • pp.810-815
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    • 2003
  • Flow-induced noise propagated from flow over a sphere is numerically investigated for laminar flow at Re = 300 and 425, and for turbulent flow at Re = 3700 and $10^4$, where the Reynolds number is based on the freestream velocity and the sphere diameter. The numerical method used for obtaining the flow over a sphere is based on an immersed boundary method in a cylindrical coordinate system. The Curle’s solutions of the Lighthill’s acoustic analogy with and without the far-field and compact-source approximation are used in order to investigate the noise field from flow over a sphere. Since the drag and lift forces change irregularly in time at Re = 425, 3700 and $10^{4}$, the noise propagates in a complicated manner. At Re = 300, 425 and $10^{4}$, the noise from dipole sources is much larger than that from quadrupole sources. On the other hand, at Re = 3700, the quadrupole source becomes dominant. The temporal variation of the flow-induced noise around a sphere is obtained at some observation points, which shows that the peak frequency corresponds to the Strouhal number associated with the wake instability.

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Combining CFD/FEM/BEM/SEA to Predict Interior Vehicle Wind Noise - Validation Case CAA German Working Group (자동차 유동기인 실내소음 예측을 위한 CFD/FEM/BEM/SEA 의 조합 및 검증 - CAA German Working Group)

  • Blanchet, D.;Golota, A.
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2014.10a
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    • pp.800-811
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    • 2014
  • Recent developments in the prediction of the contribution of windnoise to the interior SPL have opened a realm of new possibilities in terms of i) how the convective and acoustic sources terms can be identified, ii) how the interaction between the source terms and the side glass can be described and finally iii) how the transfer path from the sources to the interior of the vehicle can be modelled. This work discusses in details these three aspects of wind noise simulation and recommends appropriate methods to deliver required results at the right time based on i) simulation and experimental data availability, ii) design stage at which a decision must be made and iii) time available to deliver these results. Several simulation methods are used to represent the physical phenomena involved such as CFD, FEM, BEM, FE/SEA Coupled and SEA. Furthermore, a 1D and 2D wavenumber transformation is used to extract key parameters such as the convective and the acoustic component of the turbulent flow from CFD and/or experimental data whenever available. This work focuses on the validation of the wind noise source characterization method and the vibro-acoustic models on which the wind noise sources are applied.

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The Effect of Scaling of Owl's Flight Feather on Aerodynamic Noise at Inter-coach Space of High Speed Trains based on Biomimetic Analogy

  • Han, Jae-Hyun;Kim, Tae-Min;Kim, Jung-Soo
    • International Journal of Railway
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    • v.4 no.4
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    • pp.109-115
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    • 2011
  • An analysis and design method for reducing aerodynamic noise in high-speed trains based on biomimetics of noiseless flight of owl is proposed. Five factors related to the morphology of the flight feather have been selected, and the candidate optimal shape of the flight feather is determined. The turbulent flow field analysis demonstrates that the optimal shape leads to diminished vortex formation by causing separation of the flow as well as allowing the fluid to climb up along the surface of the flight feather. To determine the effect of scaling of the owl's flight feather on the noise reduction, a two-fold and a four-fold scaled up model of the feather are constructed, and the numerical simulations are carried out to obtain the aerodynamic noise levels for each scale. Original model is found to reduce the noise level by 10 dBA, while two-fold increase in length dimensions reduces the noise by 12 dBA. Validation of numerical solution using wind tunnel experimental measurements is presented as well.

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Reduction of Aerodynamic Noise for a High-Speed Slim-Type Optical Disk Drive by Applying the Principle of Resonator (공명기를 이용한 고배속 슬림형 드라이브의 유동기인 소음저감에 관한 연구)

  • Yang, Tae-Man;Choi, Moon-Ho;Rhim, Yoon-Chul;Lee, In-Hwan;Lee, Han-Beak;Cha, Ik-Joo
    • Transactions of the Society of Information Storage Systems
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    • v.3 no.4
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    • pp.196-201
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    • 2007
  • As the demand for the lap-top computer has been increased, most users ask quiet environment to work comfortably. Therefore, noise problems of an ODD are of great interest. For the high speed ODD, the flow induced noise is caused by the turbulent flow[1], which is known to be a major source of overall noise of a slim type ODD. In this study, we introduce a new attempt to reduce the noise level using the concept of Helmholtz resonator[2].The experimental analysis is carried out for several cases at different resonance frequencies and different hole patterns. The results show reductions in the noise level from the acoustic noise absorption point of view.

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Noise and vibration reductions in exhaust duct system of cogeneration power plants (열병합발전소 배기 덕트 시스템의 소음 진동 저감)

  • Kim, W.H.;Joo, W.H.;Bae, J.G.
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2004.11a
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    • pp.641-646
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    • 2004
  • Noise and vibration was encountered in exhaust duct system which is connected with a gas turbine and a heat recovery steam generator(HRSG) of a cogeneration power plants. Especially, these problems occurred when water was added to the fuel injection to reduce NOx contents of the exhaust gas. Through the cavity mode analysis and measurements, It was concluded that these problems occurred due to the acoustic resonance between the duct cavity mode and the excitation force induced by turbulent gas flow during water injection. To reduce the noise and vibration, optimal baffle plate to change the cavity mode was installed inside of duct and noise levels of about 8 dB(A) are reduced in duct system. The effects of baffle plate and guide vane to the HRSG or inlet duct vibration were also evaluated and it was verified that there is no relation to the resonance phenomena. So, vibration of inlet duct was easily reduced by the reinforcement of structures.

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Estimation and Application of Turbulent Flow-Induced Input Power for Vibrational Power Flow Analysis (진동파워흐름해석을 위한 난류흐름에 의한 입력파워 추정 및 적용)

  • Lim, Gu-Sub;Hong, Suk-Yoon;Park, Young-Ho;Choi, Young-Dal;Joung, Tea-Seok
    • Special Issue of the Society of Naval Architects of Korea
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    • 2008.09a
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    • pp.96-105
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    • 2008
  • Turbulent flow-induced vibrations generate the structural fatigue and noise problems. In this paper, using Corcos, Smol' yakov-Tkachenko, Ffowcs Williams and Chase models, the input power generated by distributed fluid force is predicted for power flow analysis (PFA) of turbulent flow-induced vibration. Additionally, the Fast Fourier Transform (FFT) is used to raise the calculation efficiency PFA results obtained are compared with the classical modal solutions for verifications. Analytic results using the fluid models show good agreements with those of modal analysis, respectively.

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Experimental Study on the Three-Dimensional Topology of Hairpin Packet Structures in Turbulent Boundary Layers (난류경계층의 3차원 헤어핀 다발구조에 대한 실험적 연구)

  • Kwon, Seong-Hun;Yoon, Sang-Youl;Kim, Kyung-Chun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.7
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    • pp.834-841
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    • 2004
  • Experimental study on the three-dimensional topology of hairpin packet structures in turbulent boundary layers were carried out. Two different Reynolds number based on momentum thickness, Re$\sub$$\theta$/=514 and 934 were generated in a blowing type wind tunnel under the condition of zero pressure gradient. Simultaneous measurements of velocity fields at a wall-normal plane and wall-parallel plane by a plane PIV and a Stereo-PIV systems. The two Nd:Yag laser systems and three CCD cameras were synchronized to obtain instantaneous velocity fields at the same time. To avoid optical noise at the crossing line by the two laser light sheets, a new optical arrangement using polarization was applied. The obtained velocity fields show the existence of hairpin packet structure vividly and the idealized hairpin vortex signature is confirmed by experiment. Two counter-rotating vortex pair which reflects the cutting plane of hairpin legs are found both side of a strong streaky structure when the wall-normal plane cuts the hairpin head.

A Study on the Noise Reduction through the Control of Internal Flow for a Slim Type External ODD (슬림타입 외장형 ODD 내부의 유동 안정을 통한 소음저감에 관한 연구)

  • Lee, Woo-Jin;Seo, Jun-Ho;Rhim, Yoon-Chul
    • Transactions of the Society of Information Storage Systems
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    • v.8 no.2
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    • pp.72-77
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    • 2012
  • The demand for the laptop computer has been increased day by day and most of users ask quiet computer and devices to work in comfortable environment. One of the devices which generate acoustic noise is an external ODD. Unlike the internal ODD, the external ODD is easy to emit noise because it runs outside of the computer and also it is packed with a thin plastic covers. As the disk rotates, vortex flow is generated inside of the cavity due to various and complicated mold parts of the cover. In addition, there is a gap between the disk tray and the upper/lower cases, through which the air flows as well as the noise leaks. In this study, we have proposed how to reduce the acoustic noise of an external ODD using numerical and experimental analysis. The pressure fluctuations and turbulent kinetic energy distributions are calculated for the developed model. The results show that the sound pressure level is reduced by 2.3dB through simple modifications of ribs of the top cover, which remove or suppress flow instabilities inside of the cavity.

Modal acoustic power of broadband noise by interaction of a cascade of flat-plate airfoils with inflow turbulence (평판 에어포일 캐스케이드와 입사 난류의 상호작용에 의한 광대역 소음의 모달 음향 파워)

  • Cheong, Cheol-Ung;Jurdic, Vincent;Joseph, Phillip
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2007.11a
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    • pp.1467-1475
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    • 2007
  • This paper investigates the modal acoustic power by a cascade of flat-plate airfoils interacting with homogeneous, isotropic turbulence. Basic formulation for the acoustic power upstream and downstream is based on the analytical theory of Smith and its generalization due to Cheong et al. The acoustic power spectrum has been expressed as the sum of cut-on acoustic modes, whose modal power is the product of three terms: a turbulence series, an upstream or downstream power factor and an upstream or downstream acoustic response function. The effect of these terms in the modal acoustic power has been examined. For isotropic turbulence gust, the turbulent series are only reducing factor of the modal acoustic power. The power factor tends to reduce the modal acoustic power in the upstream direction, although the power factor is liable to increase the modal acoustic power in the downstream direction. The modes close to cut-off are decreasing strongly, especially in the downstream direction. Therefore the modes close to cut-off don't contribute highly to the radiated acoustic power in the downstream direction, although the modal acoustic pressure is high for these modes.

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Computation of Broadband Noise of a 2-B Flat-airfoil Cascade Subject to Ingested Turbulence (난류 와류의 입사에 의한 이차원 평판 에어포일 캐스케이드의 광대역 소음장의 계산)

  • Cheong, Cheolung;Joseph Phillip;Lee, Soogab
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.15 no.6 s.99
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    • pp.687-696
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    • 2005
  • Acoustic power spectrum of the upstream and downstream sound field due to an isotropic frozen turbulent gust impinging on a cascade of flat plate airfoils are computed by using a analytic formulation derived from Smith's method, and Whitehead's LINSUB codes. A parametric study of the effects on sound power of the number of blades and turbulence length scale is performed with an emphasis on analyzing the characteristics of sound power spectrum. Through the comparison of the computed results of sound power, it is found that acoustic power spectrum from the 2-D cascade subject to a ingested turbulence can be categorized into two distinct regions. one is lower frequency region where some spectral components of turbulence do not contribute to the cut-on acoustic modes and therefore the effect of the cascade geometry is more dominant ; the other is higher frequency region where all of spectral components of turbulence make contributions to cut-on acoustic modes and thus acoustic power is approximately proportional to the blade number.