• International Journal of Aeronautical and Space Sciences
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• 제18권1호
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• pp.144-153
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• 2017

In recent years, unmanned aerial vehicles (UAVs) have been developed and studied for various applications, including drone deliveries, broadcasting, scouting, crop dusting, and firefighting. To enable the wide use of UAVs, their exact aeroacoustic characteristics must be assessed. In this study, a noise prediction method for a ducted fan UAV with complicated geometry was developed. In general, calculation efficiency is increased by simulating a ducted fan UAV without the struts that fix the fuselage to the ducts. However, numerical predictions of noise and aerodynamics differ according to whether struts are present. In terms of aerodynamic performance, the total thrust with and without struts is similar owing to the tendency of the thrust of a blade to offset the drag of the struts. However, in aeroacoustic simulations, the strut effect should be considered in order to predict the UAV's noise because noise from the blades can be changed by the strut effect. Modelling of the strut effect revealed that the dominant tonal noises were closely correlated with the blade passage frequency of the experimental results. Based on the successful detection of noise sources from a ducted fan UAV system, using the proposed noise contribution contour, methods for noise reduction can be suggested by comparing numerical results with measured noise profiles.

• 한국소음진동공학회논문집
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• 제12권1호
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• pp.42-47
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• 2002

Sirocco fans are widely used in HVAC and air conditioning systems, and the noise generated by these machines causes one of the most serious problems. In general, the sirocco fan noise is often dominated by tones at BPF(blade passage frequency) and broadband noise. However, only a few researches have been carried out on predicting the aeroacoustic 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 develop a prediction method for the unsteady flow field and the acoustic pressure field of a sirocco 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 by the unsteady Bernoulli equation. Lowson\`s method is used to predict the acoustic source. Reasonable results are obtained not only fur the tonal noise but also far the amplitudes of the broadband noise. Acoustic pressure is proportional to (Ω)2.3, which is the similar value with the measured data.

• 한국음향학회지
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• 제33권1호
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• pp.40-47
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• 2014

원심팬 날개 깃에서 발생한 와류와 원심팬 볼루트 사이의 상호작용은 원심팬의 주요한 소음원으로 알려져 있다. 본 연구에서는 저소음 설계의 기초 자료로 활용하기 위하여 원심팬의 주요한 소음원 영역으로 고려되는 원심팬 볼루트 영역을 세분화하여 볼루트 영역내의 상대적 기여도를 분석한다. 주요한 소음원으로부터 방사되는 소음을 예측하기 위해 내부 음장용 복합 전산공력음향학(CAA, Computational Aero-Acoustics) 방법을 사용한다. 이 방법은 전산유체역학(CFD, Computational Fluid Dynamics)과 음향상사법(Acoustic Analogy), 그리고 경계요소법(BEM, Boundary Element Method)을 사용하여 원심팬 내부 유동장으로부터 방사한 소음을 원심팬 외부 음향장에서 예측하는 방법이다. 복합 CAA 방법을 이용한 원심팬 볼루트 영역내의 소음원의 상대적 기여도 분석은 컷-오프영역으로부터 출구영역보다 컷-오프영역으로부터 원심팬 스크롤영역이 전체 소음에 대한 기여도가 높고, 날개 깃의 쉬라우드 영역보다 허브 영역이 전체 소음에 대한 기여도가 높다는 것을 보여준다. 이러한 결과는 향후 저소음 원심팬 개발을 위한 유용한 자료로 활용될 것이다.

• 한국음향학회지
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• 제31권6호
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• pp.391-398
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• 2012

본 연구에서는 기존의 RANS(Reynolds Averaged Navier Stokes) 방정식을 이용하는 복합 CAA(Computational AeroAcoustics) 방법에 광대역 소음원 생성을 위한 FRPM(Fast Random Particle Mesh) 기법을 적용하여 원심팬 광대역 소음 예측을 수행하였다. 먼저, RANS 방정식을 이용하여 원심팬 주위의 유동장을 예측하여 주요한 소음원 영역을 추론하고, 추론된 소음원 영역에 FRPM 기법을 적용하여 통계적 특성을 만족하는 난류를 재생하였다. RANS 방정식으로부터 해석된 유동장과 FRPM 기법으로부터 재생된 유동장을 이용하여 합성한 유동장에 음향상사법(Acoustic Analogy)을 적용하여 원심팬의 소음원을 생성하였다. 생성된 원심팬의 소음원을 경계요소법(Boundary Element Method)으로 구현된 선형전파모델에 적용하여 원심팬의 광대역 소음을 예측하였다. 원심팬에 대한 소음 측정값과의 비교를 통하여 제안된 기법이 원심팬의 순음 소음 및 광대역 소음 예측에 효과적임을 확인하였다.

• Journal of Mechanical Science and Technology
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• 제18권2호
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• pp.185-192
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• 2004

The aeroacoustic characteristics of a centrifugal fan for a vacuum cleaner and its noise reduction method are studied in this paper. The major noise source of a vacuum cleaner is the centrifugal fan. The impeller of the fan rotates at over 30000 rpm, and generates very high-level noise. It was revealed that the dominant noise source is the aerodynamic interaction between the rotating impeller and stationary diffuser. The directivity of acoustic pressure showed that most of the noise propagates backward direction of the fan-motor assembly. In order to reduce the high tonal sound generated from the aerodynamic interaction, unevenly pitched impeller and diffuser, and tapered impeller designs were proposed and experiments were performed. Uneven pitch design of the impeller changes the sound quality while the overall sound power level (SPL) and the performance remains similar. The effect of the tapered design of impeller was evaluated. The trailing edge of the tapered fan is inclined. This reduces the flow interaction between the rotating impeller and the stationary diffuser because of some phase shifts. The static efficiency of the new impeller design is slightly lower than the previous design. However, the overall SPL is reduced by about 4 dB(A). The SPL of the fundamental blade passing frequency (BPF) is reduced by about 6 dB (A) and the 2$\^$nd/ BPF is reduced about 20 dB (A). The vacuum cleaner with the tapered impeller design produces lower noise level than the previous one, and the strong tonal sound was dramatically reduced.

• 한국정밀공학회지
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• 제22권3호
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• pp.46-51
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• 2005

The vacuum cleaner motor runs at very high speed for suction power. Specially, motor power is provided by the impeller being rotated at very high speed. The centrifugal fan consists of the impeller, the diffuser, and the circular casing. Due to the high rotating speed of the impeller and small gap distance between the impeller and the diffuser, the level of noise in the centrifugal fan is at BPF(Blade Passage Frequency) and its harmonic frequencies. In order to calculate the sound pressure of centrifugal fan, unsteady flow data are needed. The cause of noise is obtained by dividing the fluid noise by exhaust flow of fan and vibration noise by rotational vibration of vacuum cleaner fan motor. Until now, an accelerometer has been used to measure vibration. However, it can not measure vibration in some parts of brush and commutator because of motor construction and 3-D vibrating mode. This study was conducted to perform accurate analysis of vibration and aerodynamic sound for fan motor in a vacuum cleaner using a laser vibration analyzer. A silent fan motor can be designed using the data measured in this study.

• 전기학회논문지
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• 제62권9호
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• pp.1217-1222
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• 2013

It is very important to diminish noise source of electric motor systems that are used for home appliance area. We have studied on the noise reduction of BLDC motor, mainly focusing on reducing noise source from cogging torque. This noise source causes resonance of fan & motor systems. This study showed that the higher harmonic component of the cogging torque was the main factor for noise generation. Therefor, to reduce noise of bldc motor for refrigerator, this study suggested peanut shaped magnet which surface flux has similar sinusoidal wave form.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.658-664
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• 2002

Unsteady flow characteristics and associated blade tonal noise of a cross-flow fan are predicted by a computational method. The incompressible Navier-Stokes equations are time-accurately solved for obtaining the pressure fluctuations between the rotating blades and the stabilizer, and sound pressure is predicted using Curie's equation. The computed fan performance is favorably compared with experimental data, and also indicates that the performance is not significantly altered by the random pitch effect at ${\phi}>0.4$. In the present study, the narrow-band noise characteristics of three impellers with a uniform and two random Pitch (type-A and-B) blades are compared by the SPL (Sound Pressure Level) spectra, and their frequency modulation characteristics of the BPF (Blade Passing Frequency) noise are also discussed.

• 한국전산유체공학회지
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• 제15권4호
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• pp.60-66
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• 2010

Unsteady Reynolds Averaged Navier-Stokes(URANS) and Large Eddy Simulation(LES) simulation of an axial flow fan are calculated upon same conditions and computational grids in order to study aeroacoustic noise of an axial flow fan numerically. Results of computed performance and predicted noise are compared with those of measurement. Both performances show accurate results with a significant difference of less than 5%. However, noise of LES result is more close to measured noise qualitatively than URANS. Levels of tonal noises of both LES and URANS are quite similar with those of measured at BPF(Blade Passing Frequency) in sound spectrum. However, as leading edge separation and tip vortex shedding phenomena of LES are showed more clearly than those of URANS, sound level of broadband noise of LES corresponds better than that of URANS, especially.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2597-2602
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• 2007

In this paper, the performance analysis is experimentally carried out in order to select the best cooling fan and shroud considering both cooling performance and noise reduction. 4 cooling fans have been tested in the fan tester and the real excavator. In order to obtain the performance of the cooling fans, flow capacity has been estimated by measuring flow velocity using a hot wire anemometer, and noise radiation has been also measured to estimate the fan noise. Characteristics of a box-type and a streamlined shroud have been examined by changing the immersion depth of cooling fans. Based upon the results, the best cooling fan is selected. Finally, the criterion to select the best cooling fan has been set up.