• Title, Summary, Keyword: 유동소음

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Evaluation and analysis of the acoustic performance of ducted silencers based on ISO 7235 (공조용 소음기의 성능시험 평가 및 분석 (ISO 7235))

  • Kim, Doo-Hoon
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.191-196
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    • 2000
  • 본 논문에서는 공조용 소음기에 대한 삽입손실 및 압력손실과 같은 음향성능 평가를 위해 필요한 제반 사항을 ISO 7235에 근거하여 소개하였다. 이를 위해 시험설비의 종류 및 구비조건, 측정방법, 측정시 유의사항 등을 기술하였고, 이로서 공조용 소음기의 보다 정확한 음향성능평가가 이루어지도록 검토 하였다.

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A Numerical Study on the Generation and Propagation of Intake Noise in the Reciprocating Engine (엔진 흡기계의 소음발생 및 전파에 관한 수치연구)

  • 김용석;이덕주
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.65-70
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    • 1996
  • 엔진소음을 소음특성에 따라 분류하면 공력소음(Aerodynamic Noise), 연소소음(Combustion Noise), 기계적인 소음(Mechanical Noise)으로 나눌 수 있으며 소음원의 종류에 따라 분류하면 배기계소음(Exhaust System Noise)으로 나눌 수 있으며 소음원의 종류에 따라 분류하면 배기계소음(Exhaust System Noise), 흡기계소음(Intake System Noise), 냉각계소음(Cooling System Noise), 엔진표면소음(Engine System Noise)등으로 분류할 수 있다. 이러한 여러소음중 엔진 내부의 유동에 의한 흡배기계통으로의 소음방출은 자동차 실 내외 소음의 중요한 문제로 대두되는데, 이를 줄이기 위해 그 동안 소음기 등의 서브시스템의 형태와 그 위치조정에 관한 연구가 수행되어 왔다. 그러나 이것이 비용 또는 성능에 영향을 미치므로 본질적인 소음원을 규명해 내는 것이 필요하게 되었다. 흡배기계의 소음은 엔진의 흡입, 배기행 정시 피스톤의 운동에 의해 팽창 및 압축파 형태의 압력파(pressure wave)로 발생하게 되고, 밸브근방에서는 유동의 박리(separation)에 의해 발생하게 된다. 소음기 등의 서브시스템에서도 유동의 박리에 의해 발생하게 되며 특히 배기행정시 발생하는 압력파는 비선형영역에 있게된다. 흡기소음은 배기에 비해 그 크기가 작아서 그동안 등한시 되어왔으나 이것이 소비자의 불평요인으로 작용하므로써 이에 대한 연구도 활발히 수행되어야 한다. Bender, Bramer[1]는 흡배기계 소음의 외부 방사에 관하여 전반적으로 기술하였고 Sierens등[2]은 흡기계에서 1차원 MOC(Method of Characteristics)방법으로 비정상 유동해석을 하고 실험결과와 비교하였다. J.S.Lamancusa 등[3]은 흡기 소음원을 실험을 통해 예측하였고, 흡기소음도 비선형 거동을 보인다고 밝혔다. Yositaka Nishio 등[4]은 새로운 흡기실험장치를 고안하여 공명기(resonator)의 위치 변화에 의한 저소음 흡기계를 설계 초기단계에서부터 적용하려 하였다. 일반적으로 흡배기계의 복잡한 형상 때문에 대부분 실험을 통해 문제를 해결하려 하였고, 수치해석은 피스톤의 운동을 배제한 단순화한 흡배기계의 정상상태 유동해석이 주를 이루어왔다. Taghaui and Dupont 등[5]은 KIVA코드를 사용하여 흡기포트와 연소실 그리고 밸브의 움직임을 동시에 고려한 수치해석을 도입하였다. 하지만 이들이 밸브의 운동을 고려하기 위해 사용한 이동격자는 격자점은 시간에 따라 변화하지만 그 격자의 수가 일정하게 유지되어 있어서 밸브의 완전개폐를 해석할 수가 없다. 강희정[6]은 단일 실린더와 단일 배기밸브를 갖는 문제로 단순화하여 피스톤과 밸브의 움직임을 고려하므로써 배기행정 후 소음이 어떻게 전파해 나가는가를 연구하였다. 본 연구에서도 최소밸브간격과 최대밸브간격 사이에서만 계산이 가능하나 흡기의 경우는 밸브가 닫힐 때 생기는 압력파가 중요하므로 실린더와 밸브사이에 벽면조건을 주어 밸브의 개폐를 모사하였다.

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Study on the flow and noise characteristic analysis for cooling fan in a server computer (서버용 냉각팬의 유동 및 소음 특성 분석에 관한 연구)

  • Lim, Tae-Gyun;Jeon, Wan-Ho;Hong, Hyun-Ki
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.773-778
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    • 2014
  • Recently both high performance and low noise for a cooling fan used in a server computer have been required. In this study, we measured the noise characteristics for a small cooling fan used in a computer or in a server, and compared the computational data to measured ones. SC/Tetra V10 and FlowNoise V4.3 was used for the unsteady flow field and the aeroacoustic analysis, respectively. The aeroacoustic analysis results have the good agreement with measured data within 3% errors in overall SPL. In the noise spectrum, we could find the peak tonal noise at lower frequency than 1st BPF, and confirm that the reason is caused by the asymmetry of bell mouth shape.

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Evaluation of Noise Reduction Performance of HVAC System for Ships (선박용 HVAC 시스템의 소음저감성능 평가)

  • Kim, Sang-Ryul;kim, Hyun-Sil;Kim, Jae-Seung;Kim, Bong-Ki;Lee, Sung-Hyun
    • The Journal of the Acoustical Society of Korea
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    • v.29 no.8
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    • pp.497-503
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    • 2010
  • In this paper, evaluation of noise reduction performance of HVAC system for ships by means of HVAC mock-up system is presented. Test is done for six different types of HVAC elements including room unit, silencer, etc. It is found that when diameter of silencer is small and air flow is large, flow noise degrades insertion loss. However, as diameter of silencer becomes larger, the effect of flow noise becomes smaller, and insertion loss up to 25 dB is measured. It is observed that insertion loss of diffuser type room unit is usually between zero and 10 dB, whereas that of the nozzle type room unit can be down to - 15 dB. In addition, it is shown that changing duct arrangement can reduce cabin noise by up to 2 dB, and providing same air flow to each room unit is crucial for generating less noise.

Turbulent-Induced Noise around a Circular Cylinder using Permeable FW-H Method (Permeable FW-H 방법을 이용한 원형 실린더 주변의 난류유동소음해석)

  • Choi, Woen-Sug;Hong, Suk-Yoon;Song, Jee-Hun;Kwon, Hyun-Wung;Jung, Chul-Min
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.20 no.6
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    • pp.752-759
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    • 2014
  • Varieties of research on turbulent-induced noise is conducted with combinations of acoustic analogy methods and computational fluid dynamic methods to analyze efficiently and accurately. Application of FW-H acoustic analogy without turbulent noise is the most popular method due to its calculation cost. In this paper, turbulent-induced noise is predicted using RANS turbulence model and permeable FW-H method. For simplicity, noise from 2D cylinder is examined using three different methods, direct method of RANS, FW-H method without turbulent noise and permeable FW-H method which can take into account of turbulent-induced noise. Turbulent noise was well predicted using permeable FW-H method with same computational cost of original FW-H method. Also, ability of permeable FW-H method to predict highly accurate turbulent-induced noise by applying adequate permeable surface is presented. The procedure to predict turbulent-induced noise using permeable FW-H is established and its usability is shown.

Numerical investigation of blade tip vortex cavitation noise using Reynolds-averaged Navier-Stokes simulation and bubble dynamics model (Reynolds-averaged Navier-Stokes 해석과 기포동역학 모델을 이용한 날개 끝 와류 공동 소음의 수치적 고찰)

  • Ku, Garam;Cheong, Cheolung;Seol, Hanshin
    • The Journal of the Acoustical Society of Korea
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    • v.39 no.2
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    • pp.77-86
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    • 2020
  • In this study, the Eulerian/Lagrangian one-way coupling method is proposed to predict flow noise due to Blade-Tip Vortex Cavitation (BTVC). The proposed method consists of four sequential steps: flow field simulation using Computational Fluid Dynamics (CFD) techniques, reconstruction of wing-tip vortex using vortex model, generation of BTVC using bubble dynamics model and acoustic wave prediction using the acoustic analogy. Because the CFD prediction of tip vortex structure generally suffers from severe under-prediction of its strength along the steamwise direction due to the intrinsic numerical damping of CFD schemes and excessive turbulence intensity, the wing-tip vortex along the freestream direction is regenerated by using the vortex modeling. Then, the bubble dynamics model based on the Rayleigh-Plesset equation was employed to simulate the generation and variation of BTVC. Finally, the flow noise due to BTVC is predicted by modeling each of spherical bubbles as a monople source whose strength is proportional to the rate of time-variation of bubble volume. The validity of the proposed numerical methods is confirmed by comparing the predicted results with the measured data.

Experimental and Analytical Study on the Flow Noise Reduction of Construction Equipment (건설장비의 유동 소음 저감을 위한 해석 및 실험적 연구)

  • Kim, Hyung-Taek;Joo, Won-Ho;Bae, Jong-Gug
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.242-243
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    • 2010
  • The cooling system, including a fan is a one of the major sources to generate the radiated noise of construction equipment. Therefore, it is required to reduce the flow noise induced by a fan in order to reduce the noise level. In this study, we made an engine room model to carry out a variety of experiments. And then, the flow noise analysis technique using the CFD code was applied to the cooling system of construction equipment. These analyses results agree well with the measurement results. These results make it possible to understand the flow noise characteristics and to design the low noise cooling system in the design stage.

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Analysis of flow characteristics around the sunroof opening variation with sunroof deflector angle (썬루프 디플렉터 각도에 따른 썬루프 개구부 주변 유동 특성 연구)

  • Lee, Sung Won;Shin, Seongryong;Choi, Eui Sung;Yi, Juwan
    • The Journal of the Acoustical Society of Korea
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    • v.37 no.5
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    • pp.285-291
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    • 2018
  • In the present study, flow characteristics and wind noises around the sunroof opening are analyzed variation with panoramic sunroof deflector angle. A mesh deflector is attached to reduce wind noise while a car is driving with the panoramic sunroof opening. A new forward inclined type deflector was invented to improve wind noise. The effect of this new concept of mesh deflector on the open-panoramic flow characteristics and wind noises were studied with CAT (Computer Aided Test) and wind tunnel test, which shows the reduction of open-panoramic wind noises such as sunroof buffeting, sunroof booming, and turbulent noise. Therefore, the forward inclined type deflector can efficiently improve wind noise with the same production cost.

Broadband Noise Prediction of the Ice-maker Centrifugal Fan in a Refrigerator Using Hybrid CAA Method and FRPM Technique (복합 CAA 방법과 FRPM 기법을 이용한 냉장고 얼음제조용 원심팬의 광대역 소음 예측)

  • Heo, Seung;Kim, Dae-Hwan;Cheong, Cheol-Ung
    • The Journal of the Acoustical Society of Korea
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    • v.31 no.6
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    • pp.391-398
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    • 2012
  • In this paper, prediction of centrifugal fan was conducted through combination the hybrid CAA method which was used to predict the fan noise with the FRPM technique which was used to generate the broadband noise source. Firstly, flow field surround the centrifugal fan was computed using the RANS equations and noise source region was deducted from the computed flow field. Then the FRPM technique was applied to the source region for generation of turbulence which satisfies the stochastic features. The noise source of the centrifugal fan was modeled by applying the acoustic analogy to the synthesized flow field from the computed and generated flow fields. Finally, the broadband noise of the centrifugal fan was predicted through combination the modeled noise source with the linear propagation which was realized using the boundary element method. It was confirmed that the proposed technique is efficient to predict the tonal and broadband noises of centrifugal fan through comparison with the measured data.

An Experimental Study on Flow Noise with Swirl in a 180 Degree Circular Tube (선회가 있는 180°원형 곡관의 유동소음에 대한 실험적 연구)

  • Chang, Tae-Hyun
    • Journal of Advanced Marine Engineering and Technology
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    • v.33 no.6
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    • pp.903-911
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    • 2009
  • During the past three or four decades, the characteristics of turbulent swirling flow have been studied extensively because of their scientific and academic importance. This research deal with the periodic flow oscillation with and without swirling flow in a 180 degree circular tube using hot wire anemometry, microphone and accelerometer. The frequency regions are observed through the structured oscillation from spectrum. This work carried out to measure the sound level by using hot wire anemometry, microphone and accelerometer for each Reynolds number, $6{\times}10^4$, $8{\times}10^4$ and $1{\times}10^5$ respectively at the entry of the test tube with and without swirl flow.