• 한국유체기계학회 논문집
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• 제2권3호
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• pp.45-51
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• 1999

Centrifugal fans are widely used and the noise generated by these machines causes one of the most serious problems. In general, the centrifugal fan noise is often dominated by tones at BPF(blade passage frequency) and its higher harmonics. This is a consequence of the strong interaction between the flow discharged from the impeller and the cutoff in the casing. However, only a few researches have been carried out on predicting the noise due to the difficulty in obtaining detailed information about the flow field and casing effects on noise radiation. The objective of this study is to develop a prediction method for the unsteady flow field and the acoustic pressure field of a centrifugal fan and to calculate the effects of rotating velocity, flow rate, cut-off distance and the number of blades and its effects on the noise of the fan. We assume that the impeller rotates with a constant angular velocity and the flow field around the impeller is incompressible and inviscid. So, a discrete vortex method (DVM) is used to model the centrifugal fan and to calculate the flow field. The force of each element on the blade is calculated with the unsteady Bernoulli equation. Lowson's method is used to predict the acoustic source. The cut-off distance is the most important factor effecting the noise generation. Acoustic pressure is proportional to 2.8, which shows the same scaling index as the experimental result. In this paper, the cut-off distance is found to be the dominant parameter offecting the acoustic pressure.

• 대한기계학회논문집B
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• 제25권9호
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• pp.1157-1164
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• 2001

Centrifugal fans are widely used and the noise generated by these machines causes one of the most serious problems. In general, the centrifugal fan noise is often dominated by tones at BPF(blade passage frequency) and its higher harmonics. This is a consequence of the strong interaction between the flow discharged from the impeller and the cutoff in the casing. However, only a few research have been carried out on predicting the noise because of the difficulty in obtaining detailed information about the flow field and casing effects on noise radiation. The objective of this study is to understand the generation mechanism of sound and to develop a prediction method for the unsteady flow field and the acoustic pressure field of a centrifugal fan. We assume that the impeller rotates with a constant angular velocity and the flow field of the impeller is incompressible and inviscid. So, a discrete vortex method(DVM) is used to model the centrifugal fan and to calculate the flow field. The force of each element on the blade is calculated by the unsteady Bernoulli equation. Lowsons method is used to predict the acoustic source. In order to compare the experimental data, a centrifugal impeller and wedge introduced by Weidemann are used in the numerical calculation and the results are compared with the experimental data. Reasonable results are obtained not only for the peak frequencies but also for the amplitudes of the tonal.

• 한국유체기계학회 논문집
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• 제5권3호
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• pp.15-24
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• 2002

This paper presents an experimental study on the unsteady flow phenomena such as leakage flow and rotating stall which have influences on the performance and stability of an axial flow fan. For this study, unsteady pressure were measured using high frequency pressure transducers mounted on the easing wall of rotor passage and analyzed by Double Phase-Locked Averaging Technique. As the flow rate was reduced to near stall point, the pressure difference between the pressure and the suction side of the blade was increased especially new the leading edge and the lowest pressure zone of suction side was gradually developed. From the result of unsteady pressure field on the casing wall, one period of rotating stall was divided into three zones and the flow characteristics on each zone were described in detail.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.365-370
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• 2000

A computational study on the effect of sweep angle of axial fan on its noise is performed in the present paper. The forward swept axial fan was designed by numerical optimization method incorporated with three dimensional flow analysis. The objective function was defined by the ratio of generation rate of turbulent kinetic energy to pressure head. And, two variables related with sweep angle distribution are used for design variables. The swept fan has better performance characteristics and noise level. The experimental result shows that spectrums of no-sweet and swept fans have differences in the blade passage frequency, especially in the broadband. And the overall noise level of swept fan is lower 10dB(A) than that of no-sweep fan. For the comparison of flow fields between no-sweep fan and swept fan, CFX-TASCflow computational fluid dynamics software is used. Standard k-${\varepsilon}$ model is used for the turbulence model. Distributions of pressure and turbulent kinetic energy distributions are compared in order to find what happen in the low-noise swept fan.

• 소음진동
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• 제9권5호
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• pp.955-965
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• 1999

Centrifugal fans are widely used and the noise generated by the these machines causes one of the most serious problems. In general, the centrifugal fan noise is often dominated by tones at BPF(blade passage frequency) and its higher harmonics. This is a consequence of the strong interaction between the flow discharged form the impeller and the cutoff in the casing. However, only a few researches have been carried out on predicting the noise because of the difficulty in obtaining detailed information about the flow field and casing effects on noise radiation. The objective of this study is to understand the generation mechanism of sound and to develop a prediction method for the unsteady flow field and the acoustic pressure field of a centrifugal fan. We assume that the impeller rotates with a constant angular velocity and the flow field of the impeller is incompressible and inviscid. So, a discrete vortex method (DVM) is used to model the centrifugal by the unsteady Bernoulli equation. Lowson's method is used to predict the acoustic source. A centrifugal impeller and wedge introduced by Weidemann are used in the numerical calculation and the results are compared with the experimental data. Reasonable results are obtained not only for the peak frequencies but also for the amplitudes of the tonal sound.

• 한국소음진동공학회논문집
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• 제25권2호
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• pp.75-82
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• 2015

Noises from the large scale marine propeller are calculated numerically on non-cavitation condition. The hydrodynamic analysis is carried out by potential based panel method with time marching free wake approach. The distribution of hydrodynamic loads on the propeller surface and noise signals are obtained using the unsteady Bernoulli's equation and the Farasssat's formula respectively. It turns out that the noise signal at the narrow band shows strong peak at the blade passage frequency, and the peak value at the 1/3 octave band also shows the same trend. Noise signals and directivity patterns for both the thickness and the loading noise are compared with each other. The directivity pattern for the loading noise shows minor lobe at the backward side of the rotating disc plane.

• 항공우주시스템공학회지
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• 제14권1호
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• pp.28-35
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• 2020

본 논문은 회전익 항공기의 동체에 특정 장비를 장착하기 위한 지지 구조물에서 균열이 발생하여 이를 개선하기 위한 목적으로 수행한 연구이다. 회전익 항공기 동체의 스킨(Skin) 구조물에 추가된 지지 구조물인 더블러(Doubler)는 개발 단계에서의 하중을 기반으로 설계 및 제작 되었으며, 항공기 운용 중 특정 시점에 더블러의 표면에서 균열이 발견되었다. 균열의 원인을 찾기 위해서 장비 장착 시 체결 조건으로 발생할 수 있는 원 구조물의 초기 변형을 고려하고, 항공기 날개 통과 주파수와 해당 구조물의 고유 주파수를 동특성 해석 조건으로 고려 하였다. 이러한 시나리오의 검토 결과로 초기 변형을 유발하는 패스너 체결 부위의 물리적인 틈(Gap) 제거를 위한 심(Shim)구조물을 추가하고, 두께가 보강된 더블러를 장착하였다. 개선된 설계의 구조적 검증을 위한 동특성 해석 결과를 검토하여 구조 강도의 증가를 확인하고, 더블러에 대한 피로 평가 수행을 통해 항공기 요구 수명 조건 또한 충족함을 확인하였다.