• 소음진동
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• 제6권5호
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• pp.661-669
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• 1996

Proposed is an aero-acoustic performance prediction method of axial fan. The fan aerodynamic performance is predicted by combining pitch-averaged quasi 3-D flow analysis with pressure loss models for blade boundary layer and wake, secondary flow, endwall boundary layer and tip leakage flows. Fan noise is assumed to be radiated as dipole distribution type, and its generation is assumed to be mainly due to the vortex street shed from blade trailing edge. The fluctuating pressure and lift on the blade surface are analyzed by incorporating the wake vortex stree shed from blade trailing edge. The fluctuating pressure and lift on the blade surface are analyzed by incorporating the wake vortex street model with thin airfoil theory. The aero-acoustic performance prediction results by the present method are in good agreement with the measured results of several axial fans. With the present prediction method, parametric studies are carried out to investigate the effects of blade chord length and spacing on the efficiency and the noise level of fan. In the case of lightly loaded fan, both efficiency improvement and noise reduction can be achieved by decreasing chord length or by increasing blade specing. However, when fan is designed at highly loaded condition, the noise reduction by increasing blade spacing penalizes the attaninable efficiency of fan.

• 한국유체기계학회 논문집
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• 제3권3호
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• pp.31-40
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• 2000

A computer program is developed for the prediction of the aerodynamic performance and the noise characteristics in the basic design step of axial flow fan. The flow field and the performance of fan are analyzed by using the streamline curvature computing scheme with total pressure loss and flow deviation models. Fan noise is assumed to be generated due to the pressure fluctuations induced by wake vortices of fan blades and to radiate via dipole distribution. The vortex-induced fluctuating pressure on blade surface is calculated by combining thin airfoil theory and the predicted flow field data. The predicted performances, sound pressure level and noise directivity patterns of fan by the present method are favorably compared with the test data of actual fan. Furthermore, the present method is shown to be very useful in optimizing design variables of fan with high efficiency and low noise level.

• 소음진동
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• 제8권5호
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• pp.870-878
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• 1998

The cross-flow fan which constitutes a fan-duct system with a stabilizer and a scroll casing is widely used in many air-ventilating and air-conditioning devices. Its ooperating points of high efficiency and loading conditions frequently induce a annoying sharp tonal component of discrete frequency on the noise spectrum, which is open called as a BPF(Blade-Passing-Frequency) noise and degrades the sound quality of the devices. this BPF tone has been one of the defects of the cross-flow fan. This study proposes two methods in order to reduce this tonal noise component, which are the random distributions of the fan blades and the skewed shapes of the stabilizer. The proposed methods are verified by a simple analytical model and are applied in manufacturing the cross-flow fan and the stabilizer samples. Some experiments are carried out to verify the reduction capability of BPF tones of above two schemes and the experimental results are analyzed. The comparison between two method is also carried out.

• 소음진동
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• 제10권3호
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• pp.457-464
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• 2000

Vibrations of a fan are often generated by mechanical unbalance magnetic force and air flow. These vibrations depend on the design of a fan the machining accuracy of each element and assembled conditions. An experimental study is carried out to reduce the vibration and noise of an industrial fan in this paper. In order to identify the vibration sources of a fan the signal analysis and system analysis are performed, It is shown that the industrial fan studied in this paper has a natural frequency at 144 Hz and resonance occurs when the running speed of the fan is 1750 rpm. The results may be helpful to design a fan with low vibration and noise.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 I
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• pp.529-535
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• 2001

A centrifugal fan design code was developed and packaged together with iDesignFan／sup TM／ as new models. This code generate centrifugal forward curved and backward curved bladed impeller optimally. It also predicts the aerodynamic performance and the overall sound pressure level of the rotating fan by assuming steady blade loading. The overall sound pressure level is used as an input parameter from the third loop of the designing process to acquire the most silent fan for the given aerodynamic performance parameters. With this kind of inverse design concept used in the code, the period of designing a fan is significantly shortened. A centrifugal fan design code, developed in this study and included in iDesignFan／sup TM／, predicts the aerodynamic performance such as design flow rate and static pressure. The aerodynamic performance in the design and off-design conditions is calculated by using the mean line analysis. For the steady loading calculation, the lift force distribution in a blade is used.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.279-284
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• 2002

In this study, it has been developed the program for predicting the noise spectrum of axial flow fan. The radiated acoustic pressure is expressed the discrete frequency noise peaks at BPF(Blade passage frequency) and its harmonics by Wu's method and the line spectrum at the broad band by Wright's method. And this paper presents the characteristics of a fan noise due to modify the design parameters. Accordingly, it is obtained the design parameter values for noise reduction of fan.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.116-121
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• 2002

Axial fans are widely used in heavy machines due to their ability to produce high flow rate for cooling of engines. At the same time, the noise generated by these fans causes one of the most serious problems. This work is concerned with the low noise technique of discrete frequency noise. To calculate the unsteady resultant force over the fan blade in an unsymmetric engine room. Time-Marching Free-Wake Method is used. From the calculations of unsteady force on fan blades, noise signal of an engine cooling fan is calculated by using an acoustic similarity law. Noise optimization is obtained from Neural Network which is constructed based on the calculated flow rate and noise spectrum.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.212-217
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• 2008

Acoustic noises generated during motor operation in mechanical system are from electromagnetic, mechanical, aerodynamic, and electrical sources. For identification of mechanical noise origins, misalignment, unbalance, fan shape, resonance, and vibration modes have been extensively considered to describe noise behavior. An experiment-based approach as well as a mathematical approach needs to be adopted for a realistic study into noise and vibration of the motor, because motor noise characteristics differ from type to type due to various noise sources. In this paper, a brushless DC motor for air-conditioner fan is analyzed by finite element method to identify noise source, and the analysis results are verified by experiments, and sensitivity analysis is performed by design of experiments.

• 한국소음진동공학회논문집
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• 제19권5호
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• pp.454-461
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• 2009

Internal aeroacoustics of an axial fan used for circulating cold air in refrigerators are computed by using the hybrid method where CFD, acoustic analogy and BEM techniques are utilized. The unsteady flow field around the axial fan is predicted by solving the incompressible RANS equations with the conventional CFD techniques. Then, main noise sources are extracted from this unsteady flow field predictions using Acoustic Analogy. Lastly, BPF noise generated from an axial fan are predicted using these modeled sources combined with the tailed Green function techniques, which are numerically solved by the BEM technique. This hybrid model is validated by comparing the prediction with the experiment. Then, parameter studies are carried out, which suggest a capability of the current method as a design tool for the low-noise of the current axial fan system in a refrigerator.

• 소음진동
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• 제7권1호
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• pp.99-106
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• 1997

Centrigugal fans are widely used due to their ability to achieve relatively high pressure ratios in a short axial distance compared to axial fans. Because of their widespread use, the noise generated by these machines causes one of serious problems. In general, centrigugal 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 periodic flow discharged radially from the impeller and the stator blades or the cutoff. But in vacuum cleaner fan the noise is dominated by not only the discrete tones of BPF but also broadband frequencies. In this study we investigate the mechanism of broadband noise and predict for the unsteady flow field and the acoustic pressure field associated with the centrifugal fan. DVM(discrete vortex method) is used to calculates the flow field and the Lowson's method is used to predict the acoustic pressures. From the results we find that the broadband noise of a circular casing centrifugal fan is due to the unsteady force fluctuation around the impeller blades related to the vortex shedding. The unsteady forces associated with the shed vortices at impeller and related to the interactions to the diffuser and the exit.