• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 I
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• pp.275-281
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• 2001

While basic input parameters for the performance and noise of axial fan are flow rate, pressure rise, rotating speed, and fan diameter, the geometric parameters of blade are sweep angle, solidity, and camber angle. The sweep angle does not affect fan performance much, but on fan noise significantly. Solidity and camber angle are very critical design parameters acting on the fan performance directly. The solidity and camber angle are closely related, therefore they have to be carefully determined for the low-noise and high-performance fan. In This paper, different design points are selceted and also geometric parameters are deliberately changed for the comparison of fan noise. As a result, at the same performance, the input rotational speed affects radiated noise more significantly than others. When solidity and camber angle are increased more than those by iDesignFan／sup TM／ program, more noise is experienced. The blade sweep method and blade numbers at same solidity are observed to results in different levels of performance and noise.

• 한국소음진동공학회논문집
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• 제15권10호
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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.

• 설비공학논문집
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• 제15권6호
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• pp.518-523
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• 2003

The purpose of this study was to reduce the noise emitted from the package air-conditioner. The optimum design methods of the fans ware investigated experimentally through the analysis of noise problem caused by the conventional PAC system. New PAC system had decreased 6 dBA in overall noise level as compared with the conventional system by various technology.

• 한국소음진동공학회논문집
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• 제19권8호
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• pp.795-801
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• 2009

This paper presents an optimal design of a magnetorheological(MR) fan clutch based on finite element analysis and also presents torque control of engine cooling fan using a sliding mode control. The MR fan clutch is constrained in a specific volume and the optimization problem identifies the geometric dimension of the fan clutch that minimizes an objective function. The objective function for the optimization problem is determined based on the solution of the magnetic circuit of the initially designed clutch. Under consideration of spatial limitation, design parameters are optimally determined using finite element analysis. After describing the configuration of the MR fan clutch, the viscous torque and controllable torque are obtained on the basis of the Bingham model of MR fluid. Then, a sliding mode controller is designed to control the torque of the fan clutch according to engine room temperature and control performance is evaluated through computer simulation.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2000년도 유체기계 연구개발 발표회 논문집
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• pp.129-136
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• 2000

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 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 centrifugal fan, and to calculate the effects of small vanes that are attached in original impeller - Splitter impeller. 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. The splitter impeller changes the acoustic characteristics as well as performance. Two-splitter type impeller and splitter impeller which splitter locates in jet region are good for acoustic characteristics.

• 대한기계학회논문집B
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• 제27권3호
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• pp.286-293
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• 2003

The unsteady flow characteristics and associated blade tonal noise of a cross-flow fan are predicted by computational methods. The incompressible Navier-Stokes equations are time-accurately solved for obtaining the pressure fluctuations between the rotating blades and the stabilizer. and the sound pressure is predicted using Curie's equation. The discrete noise characteristics of three impellers with a uniform and two random pitch (type-A and -B) blades are compared by their SPL (Sound Pressure Level) spectra. and the frequency modulation characteristics of the BPF (Blade Passing Frequency) noise are discussed. Besides. a mathematical model is proposed for the prediction of discrete blade tonal noise and is validated with available experimental data. The fan performance is also compared with experimental data. indicating that the random pitch effect does not significantly alter the performance characteristics at ${\phi}$ 〉 0.4

• 한국소음진동공학회논문집
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• 제26권4호
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• pp.383-390
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• 2016

In this paper, experiment and dynamics simulations were carried out to identify and reduce the out-of-plane vibration that occurs in a centrifugal fan of an air conditioner installed to a wall. In a wall-installed air conditioner, large space between a case and heat exchanger is often required for the fan to avoid the collision with the case and exchanger. This large space hinders the slim design of the air conditioner even if air conditioner market demands a slim air conditioner. In the present study, in order to determine the cause of the vibration in the centrifugal fan, the out-of-plane vibration and the physical properties were investigated, and the dynamic characteristics of the centrifugal fan were obtained by experiments. Based on these experiments, a dynamic simulation model was established to determine the cause of the out-of-plane vibration of the centrifugal fan. It was found that the main factor of out-of-plane vibration in the centrifugal fan is the axial misalignment between the centrifugal fan and the motor shaft.

• 한국소음진동공학회논문집
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• 제18권9호
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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.

• 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.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문초록집
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• pp.366.2-366
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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 Wavier-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 ø〉0.4. (omitted)