• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.168-171
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• 2005

The present study describes the prediction of the flow induced noise level of a high-speed rotating hexagonal disk and proposes the way how to reduce it. Since a hexagonal disk, which is used in the laser printer and named a polygon mirror, has six sharp comers, there are low and high pressure regions on each of six edges when it rotates. Therefore, the Pressure difference generates three dimension flow field and causes aerodynamic noise. The Ffowcs-Williams and Hawkings(FWH) method is employed for the analysis. We have measured the sound pressure levels and compared them with the computational results. The calculated sound pressure levels agree well with the experimental results. We modified the shape of the edges of a hexagonal disk to reduce the noise level and confirm their effects through numerical computation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.371-379
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• 2000

A noise prediction method of axial flow fan is developed by incorporating through-flow method and vortex shedding noise model. Fan noise is assumed to be generated due to the pressure fluctuation induced by wake vortices of fan blades and radiate as diploe distribution. The wake vortices are analyzed by combining Karman vortex street model and through-flow analysis results, and the vortex-induced fluctuating pressure on blade surface is calculated by thin airfoil theory. The predicted sound pressure levels and directivity patterns of fan noise by the present method are favorably compared with fan noise test data. Furthermore, the present method is shown to be very useful for predicting the aero-acoustic performance map of the fan operated at off-design point.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.2
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• pp.205-213
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• 2011

The characteristics of noise generation in the suction nozzle of a vacuum cleaner are analyzed numerically and experimentally. First, the flow resistance induced by each element in the suction nozzle of a vacuum cleaner with a double-blade rotary fan is investigated numerically and its relation with flow-induced noise and suction performance is examined in an anechoic room. The flow resistance and vorticity in the suction nozzle are calculated, and it is found that they are closely related to flow-induced noise and that the upper limit of noise reduction is only 4 dBA. This upper limit can be achieved by changing the design of the brush nozzle. Two methods for noise reduction by enlargement of flow-inlet area and by optimization of the number of blades are tested. Finally, the effects of each method are verified experimentally.

• 정보저장시스템학회:학술대회논문집
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• 2005.10a
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• pp.71-74
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• 2005

The present study describes the prediction of the flow induced noise level of a high-speed rotating hexagonal disk and proposes the way how to reduce it. Since a hexagonal disk, which is used in the laser printer and named a Polygon mirror, has six sharp corners, there are low and high pressure regions on each of six edges when it rotates. Therefore, the pressure difference generates three dimension flow field and causes aerodynamic noise. The Ffowcs-Williams and Hawkings (FWH) method is employed for the analysis. We have measured the sound pressure levels and compared them with the computational results. The calculated sound pressure levels agree well with the experimental results. We modified the shape of the edges of a hexagonal disk to reduce the noise level and confirm their effects through numerical computation.

• Journal of KSNVE
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• v.9 no.4
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• pp.693-702
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• 1999

We study the characteristics of airflow and sound noise induced by disk rotation in optical disk drives. The characteristics of airflow around a rotating disk surrounded by various tray structures are numerically investigated using a commercial CFD program and then compared with experimental results. Sound pressure and intensity caused by the fluid-structure interactions in the CD/DVD-ROM drive are measured, and the effect of the ariflow on the sound noise and disk vibration is discussed. In order to reduce airflow-induced noise and vibration around the rotating disk, tray geometry is modified. Both numerical and experimental studies implemented with different tray models show that the improved tray model alters the characteristics of the disk-induced airflow, causing the reduction of the airflow-induced sound level.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1789-1794
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• 2004

The present study investigates flow characteristics in an optical disc drive. Detailed knowledge of the flow characteristics is essential to analyze flow-induced noise and vibration, forced convection and flow friction loss. The ODD used in the personal computer is used for the experiment and rotating velocity of disc is under the 4500 rpm. Time-resolved velocity components and velocity spectrum are obtained using the laser Doppler anemometry (LDA). The results show that the front holes reduce now-induced noise and the position of pickup body affects flow near the window. In addition, il is possible for cooling of heat sources in an optical disc drive through measuring the flow fields under the tray.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.2 s.233
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• pp.224-231
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• 2005

The present study investigates flow characteristics in an optical disc drive (ODD). Detailed knowledge of the flow characteristics is essential to analyze flow-induced noise and vibration, forced convection and flow friction loss. The ODD used in a personal computer is used for the experiment and rotating velocity of disc is under the 4500 rpm. Time-resolved velocity component and velocity spectrum are obtained using the laser Doppler anemometry (LDA), and the flow patterns induced by rotating disc in the ODD are calculated by a commercial finite volume method at the same time. The results show that the front holes reduce flow-induced noise and the position of pickup body only affects flow near the window. Furthermore, it is possible for cooling of heat sources in the drive through measuring the flow fields under the tray. In addition, the numerical results are well matched up to the experimental results, therefore, the validation of the numerical results can be achieved. From the validation of numerical results, it is possible to predict the flow characteristics of the region where it is unable to conduct the experiment.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.1
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• pp.39-48
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• 2016

The latest research has shown that the turbulence-induced noise is important in total characteristics of flow noise. Also, turbulence-induced noise have a significant influence for performance of sonar dome. In this paper, Flow analysis is performed on vicinity of the sonar dome model using Large Eddy Simulation method. Also, direct method that extracts perturbational sound pressure, FW-H method without turbulence-induced noise and permeable FW-H method that is able to calculate turbulence- induced noise were compared in order to show turbulence effect.

• Journal of KSNVE
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• v.6 no.5
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• pp.671-677
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• 1996

This paper presents the analytical method for predicting turbulence- induced noise in the multilayered cylinder composed of an outer hose, an inner fluid and an internal core. It is assumed that an infinite axisymmetric cylinder is located horizontally in water with free stream velocity and the turbulent boundary layer (TBL) surrounding the outer hose is fully developed and homogeneous. The transfer function at the core surface due to the propagation of the pressure fluctuation within the TBL is formulated using the linearized Navier-Stockes equation for solid and fluid. In the estimation of the energy spectrum of wall pressure fluctuation, the empirical formula proposed by Strawderman based on the Corcos model is used. A general algorithm for the calculation of the pressure level at the surface of a core, that is, turbulence- induced noise, is presented. Through the detailed numerical simulation, it is found that the major noise mechanism is the propagation of the bulge wave along hose.

• International Journal of Fluid Machinery and Systems
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• v.7 no.1
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• pp.7-15
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• 2014

In the present study, a computational analysis of the flow in a centrifugal blower is carried out to predict a performance and to explain noise characteristics of the blower. Unsteady, 3D Navier-Stokes equations were solved with k-${\varepsilon}$ turbulence model using CFX software. CFD results were compared with the experimental data that is acquired from an experiment conducted with the same blower. The pressure fluctuation in the blower was transformed into the frequency domain by Fourier decomposition to find the relationship between flow behaviors and noise characteristics. Sound pressure level (SPL) which is obtained from wall pressure fluctuation at impeller outlet represents relative overall sound level of the blower well. Sound spectra show that there are some specific peak frequencies at each mass flow rate and it can be explained by flow pattern.