• Title/Summary/Keyword: 홴 광대역 소음

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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.

Prediction of Internal Broadband Noise of a Centrifugal Fan Using Stochastic Turbulent Synthetic Model (통계적 난류합성 모델을 이용한 원심홴 내부 광대역 소음 예측)

  • Heo, Seung;Kim, Dae-Hwan;Cheong, Cheol-Ung;Kim, Tae-Hoon
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.21 no.12
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    • pp.1138-1145
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    • 2011
  • The internal broadband noise of a centrifugal fan in a household refrigerator is predicted using hybrid CAA techniques based on stochastic turbulent synthetic model. First, the unsteady flow field around the centrifugal fan is predicted using computational fluid dynamics(CFD) method. Then, the turbulent flow field is synthesized by applying the stochastic turbulent synthetic technique to the predicted flow field. The aerodynamic noise sources of the centrifugal fan are modeled on a basis of the synthesized turbulent field. Finally, the internal broadband noise of the centrifugal fan is predicted using the boundary element method(BEM) and the modeled sources. The predicted noise spectrum is compared with the experimental data. It is found that the predicted result closely follows the experimental data. The proposed method can be used as an effective tool for designing low-noise fans without expensive computational cost required generally for the LES and DNS simulations to resolve the turbulence flow field responsible for the broadband noise.

Prediction of internal broadband noise of a centrifugal fan using stochastic turbulent synthetic model (통계적난류합성모델을 이용한 원심홴 내부 광대역 소음 예측)

  • Heo, Seung;Kim, Dae-Hwan;Cheong, Cheol-Ung;Kim, Tae-Hoon
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2011.10a
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    • pp.627-632
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    • 2011
  • The internal broadband noise of a centrifugal fan in a household refrigerator is predicted by using hybrid CAA technique based on stochastic turbulent synthetic model. First, the unsteady flow field around the centrifugal fan is predicted using Computational Fluid Dynamics (CFD) method. Then, the turbulent flow field is synthesized by applying the stochastic turbulent synthetic technique to the predicted flow field. The aerodynamic noise sources of the centrifugal fan are modeled on a basis of the synthesized turbulent field. Finally, the broadband noise of the centrifugal fan is predicted using Boundary Element Method (BEM) and the modeled sources. The predicted result is compared with the experimental data. It is found that the predicted result closely follows the experimental data. The proposed method can be used as an effective tool for designing low-noise fans without expensive computational cost required generally for the LES and DNS simulations to resolve the turbulence flow field responsible for the broadband noise.

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High-frequency Approximate Formulation for the Prediction of Broadband Noise of Airfoil Cascades with Inflow Turbulence (유입 난류에 의한 에어포일 캐스케이드 광대역 소음장의 고주파 근사 예측식의 개발)

  • Jung, Sung-Soo;Cheung, Wan-Sup;Lee, Soogab;Cheong, Cheolung
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.15 no.10 s.103
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    • pp.1177-1185
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    • 2005
  • This paper investigates the noise radiated by a cascade of flat-plate airfoils interacting with homogeneous, isotropic turbulence. At frequencies above the critical frequency, all wavenumber components of turbulence excite propagating cascade modes, and cascade effects are shown to be relatively weak. In this frequency range, acoustic power was shown to be approximately proportional to the number of blades. Based on this finding at high frequencies, an approximate expression is derived for the power spectrum that is valid above the critical frequency and which is in excellent agreement with the exact expression for the broadband power spectrum. The approximate expression shows explicitly that the acoustic Power above the critical frequency is proportional to the blade number, independent of the solidity, and varies with frequency as ${\phi}_{ww}(\omega/W$), where ${\phi}_{ww}$ is the wavenumber spectrum of the turbulence velocity and W is mean-flow speed. The formulation is used to perform a parametric study on the effects on the power spectrum of the blade number stagger angle, gap-chord ratio and Mach number. The theory is also shown to provide a close fit to the measured spectrum of rotor-stator interaction when the mean square turbulence velocity and length-scale are chosen appropriately.

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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Characteristics of 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 특성)

  • Cheong, Cheol-Ung;Jurdic, Vincent;Joseph, Phillip
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.18 no.1
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    • pp.61-70
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    • 2008
  • 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.

Time-domain Computation of Broadband Noise due to Turbulence - cascade Interaction (난류-캐스케이드 상호 작용에 의한 광대역 소음장의 시간영역 계산)

  • Jung, Sung-Soo;Cheung, Wan-Sup;Lee, Soo-Gab;Cheong, Cheol-Ung
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.16 no.3 s.108
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    • pp.263-269
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    • 2006
  • The objective of the present work is to develop a time-domain numerical method of broadband noise in a cascade of airfoils. This paper focuses on dipolar broadband noise sources, resulting from the interaction of turbulent inflows with the flat-plate airfoil cascade. The turbulence response of a two-dimensional cascade is studied by solving both of the linearised and the full nonlinear Euler equations employing accurate higher order spatial differencing, time stepping techniques and non-reflecting inflow/outflow boundary condition. The time-domain result using the linearised Euler equations shows good agreement with the analytical solution using the modified LINSUB code. Through the comparison of the nonlinear time-domain result using the full nonlinear Euler equations with the linear, it is found that the acoustic mode amplitude of the nonlinear response is less than that of the linear response due to the energy cascade from low frequency components to the high frequency ones. Considering the merits of the time-domain methods over the typical time-linearised frequency-domain analysis, the current method is expected to be promising tools for analyzing the effects of the airfoil shapes, non-uniform background flow, linear-nonliear regimes on the broadband noise due to turbulence-cascade interaction.

Time-domain Computation of Broadband Noise due to Turbulence-Cascade Interaction (난류-캐스케이드 상호 작용에 의한 광대역 소음장의 시간영역 계산)

  • Cheong, Cheol-Ung;Jeong, Sung-Su;Cheung, Wan-Sup;Lee, Soo-Gab
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2005.11a
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    • pp.812-817
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    • 2005
  • The objective of the present work is to develop a time-domain numerical method of broadband noise in a cascade of airfoils. This paper focuses on dipole broadband noise sources, resulting from the interaction of turbulent inflows with the flat-plate airfoil cascade. The turbulence response of a two-dimensional cascade is studied by solving both of the linearised and full nonlinear Euler equations employing accurate higher order spatial differencing, time stepping techniques and non-reflecting inflow/outflow boundary condition. The time-domain result using the linearised Euler equations shows good agreement with the analytical solution using the modified LINSUB code. Through the comparison of the nonlinear time-domain result using the full nonlinear Euler equations with the linear, it is found that the acoustic mode amplitude of the nonlinear response is less than that of the linear response due to the energy cascade from low frequency components to the high frequency ones. Considering the merits of the time-domain methods over the typical time-linearised frequency-domain analysis, the current method is expected to be promising tools for analyzing the effects of the airfoil shapes, non-uniform background flow, linear-nonliear regimes on the broadband noise due to gust-cascade interaction.

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Design of Automotive Engine Cooling Fan and Study on Noise Reduction through Modification of System (자동차용 냉각홴의 설계와 시스템 개선을 통한 저소음화 연구)

  • 김병주;강상규;김규영;이재영;이덕호;신동수
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.14 no.11
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    • pp.1107-1114
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    • 2004
  • Axial fans are widely used for automotive engine cooling device due to their ability to produce high flow rate to keep engine cool. At the same time, the noise generated by these fans causes one of the most serious problems. Especially, engine cooling fan noise in idle condition of a car is noticeable. Therefore. the high efficient and low-noise fan is seriously needed. When a new fan system is designed, system resistance and non-uniform inflow are the key factors to get the high performance and low noise fan system. In this study, aerodynamic and acoustic calculations are carried out on the automotive cooling fan and system. Effects of various design parameters are studied through the free wake analysis and experiments. Better performance and noise characteristic are obtained for the new design fan using the methodology. Furthermore through the modification of the fan system geometry parameters, the fan system produce more flow rate and become less noisy.

Fan Noise Prediction Method of Air Cooling System (공기 냉각 시스템의 홴 소음 예측 기법)

  • Lee, Chan;Kil, Hyun-Gwon
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.18 no.9
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    • pp.952-960
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    • 2008
  • Fan noise prediction method is presented for air conditioning, automobile and electronic cooling system applications where fan acts as an internal equipment having very complicated flow interaction with other various system components. The internal flow paths and distribution in the fan-applied systems such as computer or air conditioner are analyzed by using the FNM(flow network modeling). Fan noise prediction method comprises two models for the discrete frequency noise due to rotating steady aerodynamic lift and blade interaction and for the broadband noise due to turbulent boundary layer and wake vortex shedding. Based on the fan operation point predicted from the FNM analysis results and fan design parameters, the present far noise model predicts overall sound pressure level and spectrum. The predictions for the flow distribution, the fan operation and the noise level in air cooling system by the present method are well agreed with 3-D CFD and actual noise test results.