• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.645-645
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• 2009

In many practical applications of the centrifugal fan, the impeller-diffuser interaction noise is considered as a main source of fan noise. The housing for an electric motor is also expected to play an important role on noise propagation because of its complicated configuration. This study investigates the impeller-diffuser interaction noise and its sources by computing three-dimensional, incompressible flow field of the centrifugal fan in motor housing. The effect of motor case on fan noise characteristic is then investigated using the Brinkman penalization method, while the noise source associated with impeller-diffuser interaction is mathematically modeled. It is found that the present methodology combined with mathematical description of noise source provides a fairly good agreement with the experimental results, indicating that the motor housing has significant effect on noise characteristics. Finally, aeroacoustic noise prediction for various impeller-diffuser blade count ratios is conducted for noise reduction.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.4
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• pp.280-286
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• 2002

It has been long suspected that the transition region may give rise to local pressure fluctuations and radiated sound that are different from those created by the fully-developed turbulent boundary layer at equivalent Reynolds number. Experimental investigation described in this paper concerns the characteristics of pressure fluctuations at the transition. Flush-mounted microphones and hot wires are used to measure the pressure fluctuations and local flow velocities within the boundary layer in the low noise wind tunnel. From this experiment we could observe the spatial and temporal development process of T-S wave using Wigner-Ville method and find the relations between the characteristic frequency of T-S wave and free stream velocity and the boundary layer thickness based on nondimensional pressure spectra scaled on outer variables.

• The KSFM Journal of Fluid Machinery
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• v.18 no.6
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• pp.71-75
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• 2015

The flow and noise characteristics of the regenerative blower are evaluated experimentally. To decrease the noise of regenerative blower at a high frequency, we arrange the impeller vanes unevenly by special formula. The uneven pitch formular consists of the combination of trigonometric function. The magnitude of degree between each vanes and the control parameters of trigonometric functions are main design parameters for the uneven pitch. The flow characteristics of even and uneven impellers are tested by the fan tester and compared each results. The efficiency of a blower is calculated by the axial power using a dynamo system. The noise property of designed impeller is measured in an anechoic room. In this study, we certify that the uneven pitch impeller is effective in the noise reduction at a high frequency.

• Journal of the Korean Society of Visualization
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• v.15 no.3
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• pp.52-56
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• 2017

In this study, we investigate the flow characteristics of lift-type disk which behaves the up-down motion using the large eddy simulation (LES) and immersed boundary method (IBM). Also, we perform the noise analysis using pressure field at 1.35 m distance and reveal the cause of noise to observe the vortical structure analysis of flow result. It is observed that vortical structure and wind shear were generated at leading edge and tower with high velocity deficit and flow separation. High magnitude of flow noise was observed in low frequency range which is from 30 Hz to 60 Hz. It was observed that vortical structure at leading edge was generated in frequency range from 33.3 Hz to 41.6 Hz. Temporal characteristic in vortical structure at leading edge was similar to noise characteristics, having the similar frequency ranges.

• International Journal of Fluid Machinery and Systems
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• v.2 no.1
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• pp.80-91
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• 2009

In this study, a prediction theory for specific noise that is the overall characteristic of the fan has been proposed. This theory is based on total pressure prediction and broadband noise prediction. The specific noises of two forward curved fans with different number of blades were predicted. The flow around the impeller having 120 blades (MF120) was more biased at a certain positions than the impeller with 40 blades (MF40). An effective domain of the energy conversion of MF40 has extended overall than MF120. The total pressure was affected by the slip factor and pressure loss caused by the vortex flow. The suppression of a major pressure drop by the vortex flow and expansion of the effective domain for energy conversion contributed to an increase in the total pressure of MF40 at the design point. The position of maximum relative velocity was different for each fan. The relative velocity of MF120 was less than that of MF40 due to the deviation angle. The specific noise of MF120 was 2.7 dB less than that of MF40 due to the difference in internal flow. It has been quantitatively estimated that the deceleration in the relative velocity contributed to the improvement in the overall performance.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.502-507
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• 2000

This paper presents the numerical prediction of airflow-induced sound in DVD drives. Computational fluid dynamics (CFD) is first conducted to evaluate flow field characteristics due to the high-speed disk rotation, and to support the acoustic analysis. The acoustic analogy based on Ffowcs Williams-Hawkings (FW-H) equation is adopted to predict aeroacoustic noise patterns. The integral solution for quadrupole volume source is included to identify the turbulence noise generated inside the DVD tray. Near-field noise is strongly affected by the flow field characteristic, which is caused by the complex shape of the tray. For a mid-field, the quadrupole noise play as a counterpart of thickness noise or loading noise, resulting in a different pattern compared with those in the near field.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.300-305
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• 2001

The unsteady flow structure and the related noise generation, which are caused by the separation of a two-dimensional, incompressible, laminar boundary-layer on the flat plate under the influence of local adverse pressure gradient, are numerically examined. The characteristic lines of the wall pressure are examined to understand the unsteady behavior of vortex shedding near the reattachment point of the separation bubble. Also, the generation and propagation of the vortex-induced noise in the separated boundary-layer are calculated by the method of computational aero-acoustics (CAA), and the effects of Reynolds number, Mach number and the strength of the adverse pressure gradient on the unsteady flow and noise characteristics are examined.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.345-349
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• 2003

The dynamic behavior of CANDU nuclear fuel channel was analyzed by the use of 3-dimensional finite element method, under the various fault conditions such as a fault in the end fitting support and the removal/migration of the garter spring in the fuel channel, in order to predict the dynamic behavior for a degraded symptoms of CANDU nuclear fuel channel. Moreover, the frequency response analysis for possible fault conditions was also peformed considering the effects of the pressure tube vibration and flow-induced vibration by the coolant flow. From the analysis of the frequency responses, defects in the garter spring have influenced the changes of 2nd and 3rd modes and all the important modes are varied for the failure in the journal bearing in the end fitting body.

• The Journal of the Acoustical Society of Korea
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• v.33 no.6
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• pp.351-357
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• 2014

In this paper, flow noise characteristics of the hybrid vertical-axis wind turbine is investigated. Hybrid vertical-axis wind turbines consisting of two types of vertical-axis wind turbines, Savonius and Darrieus, are devised to maximize merits of one turbine and thus minimize demerits of the other turbine. In order to predict flow noise radiating from hybrid vertical-axis wind turbines, hybrid computatioinal aero acoustic techniques are used. First, unsteady flow fields around the turbine are predicted using computational fluid dynamics method. Then, the flow noise radiations from the turbines are predicted by applying acoustic analogy to the predicted flow fields. Based on numerical results, noise characteristics of a hybrid vertical-axis wind turbine is investigated and is compared with those of Savonius and Darrieus wind turbines.

• 한국가시화정보학회:학술대회논문집
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• 2003.11a
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• pp.99-102
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• 2003

PIV(Particle Image Velocimetry)was used to visualize the interaction of reed valve of the reciprocating compressor. The valve is the key part which governs the efficiency, noise and reliability of the compressor, so the development of analytical model about valve performance is necessary. As the valve reed is opened and closed by pressure pulsation, the flow characteristic of the refrigerant passing the valve is very important. In the present study, a circular disk with inclination is assumed to be the valve reed of a reciprocating compressor, The mean velocity shows the vortical characteristic of this flow. It is found that the back flow is affected by the height of reed valve of reciprocating compressor.