• The KSFM Journal of Fluid Machinery
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• v.3 no.2 s.7
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• pp.15-23
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• 2000

The present work describes the prediction method for the unsteady flow field and the acoustic pressure field of a ducted axial fan. The prediction method is comprised of time-marching free-wake method, acoustic analogy, and the Kirchhoff-Helmholtz BEM. The predicted sound signal of a rotor is similar to the experiment one. We assume that the rotor rotates with a constant angular velocity and the flow field around the rotor is incompressible and inviscid. Then, a time-marching free-wake method is used to model the 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 newly developed Helmholtz-Kirchhoff BEM lot thin body is used to calculate tile sound field of the ducted fan. The ducted fan with 6 blades is analysed and the sound field around the duct is calculated.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.755-758
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• 2002

The physical phenomena of rectangular open cavity are numerically investigated in this paper Two-dimensional cavity problems with laminar boundary layers in upstream are simulated by using the compressible Wavier-Stokes equations. The high-order and high-resolution numerical schemes are used for the evaluation of spatial derivatives and the time integration. Cross-correlation is used to analyze the characteristics of wave propagation along time and spatial. Sudden phase shifting of 90 degrees is appeared near downstream edge, and this is coincident with the phase lag suggested in original Rossiter's equation. The results give a further understanding of the physical phenomenon of noise generation, and the resonance of flow and acoustic in cavity. Moreover, modified Rossiter's equation, which is more accurate and can be applied in various conditions, is suggested. The distance from the point of vortex generation to the point of vortex collapsing acts as effective distance of cavity resonance, and the phase difference between the point of vortex collapsing and the point of acoustic source acts as phase lag. The mechanism of acoustic generation is fully understood in this paper. The mechanism of acoustic generation is fully understood in this paper.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.8
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• pp.532-538
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• 2015

In a reciprocating compressor, highly impulsive pressure fluctuations induced by a reciprocating piston give rise to serious noise and vibration problems. A muffler is frequently used to reduce this impulsive noise, but also has adverse effects on compressor performance due to additional pressure drop and heat transfer of refrigerants through it. Therefore, the flow and acoustic performances of mufflers used in a compressor should be considered simultaneously. In this study, both of flow and acoustic performances of mufflers are investigated using computational fluid dynamic techniques by solving full three-dimensional compressible Reynolds-Averaged Navier-Stokes equations. For validation purpose, the numerical method is initially applied to predict the transmission loss of a simple expansion muffler, and its predicted results show good agreements with theoretical and experimental results. Then, the flow and acoustic performances of an existing muffler is numerically investigated. On the basis of the analysis results, a new muffler is purposed and its performances are compared with the existing one. Improved performances of the new muffler are confirmed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.103-108
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• 2001

The structure of hard disk drive(HDD) is excited by dynamic motion of a disk-spindle motor, and it makes sound noise. Therefore, the cover and the base of HDD should be designed to reduce noise and vibration induced by spindle motor. The prediction technique of sound pressure level(SPL) of a given structural shape enables us to design a cover and a base with much less vibration and noise. In this paper, we measured the force of disk-spindle motor and predicted SPL from HDD by computational simulation. To get a SPL of HDD by computational simulation, modal analysis and forced vibration analysis were performed with ANSYS, and sound radiation was computed using SYSNOISE. The calculated results were compared with experimental results and a good agreement was obtained. With this computer simulation procedure and design of experiment(DOE), optimal thickness of noise barrier and damper was calculated.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.759-764
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• 2000

The accurate prediction of aeroacoustic analysis is necessary for designers to control and reduce airflow-induced sound pressure levels in high speed rotating DVD drives. This paper focuses on 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. The strength of sound pressure level with respect to rotating speed is discussed to meet upfront demand on the high fidelity product development. The present study also focuses on the noise directivity and examines how much the sound noise is sensitive to change in rotating speed. 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, so it generates different sound noise patterns compared with those in the near field.

• The Journal of the Acoustical Society of Korea
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• v.33 no.1
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• pp.40-47
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• 2014

Interaction between the unsteady flow emitted from the blade of the centrifugal fan and the volute tongue region of fan duct is known as the main noise source of the centrifugal fan. In this paper, the relative contributions of the volute tongue region of the centrifugal fan is analyzed to utilize as the foundation data of low noise design. The internal hybrid CAA (Computational Aero-Acoustics) method is used to predict noise radiated from the main noise source. This method is the noise prediction technique using CFD (Computational Fluid Dynamics), Acoustic analogy, and BEM(Boundary Element Method). The relative contributions of the centrifugal fan volute tongue region using the hybrid CAA method show that the region between the cut-off and the scroll has high contribution than the region between the cut-off and the outlet and the hub region of blade has high contribution than the shroud region of blade. These results is utilized as the important data for the development of low noise centrifugal fan.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.6
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• pp.427-435
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• 2021

An analysis considering the fluid-structure interaction is required to strictly evaluate the seismic behavior of facilities such as, environmental facilities and dams, that store fluids. Specifically, in the case of an infinite domain in the upstream direction, such as a dam-reservoir system, this should be carefully considered. In this study, we proposed a practical numerical model for both wave propagation and fluid-structure interaction analyses of an infinite domain, for a system with a semi-infinite domain such as a dam-reservoir system. This method was applicable to the time domain, and enabled accurate boundary analysis. For an infinite fluid domain, a small number of mid-point integrated acoustic finite elements were applied instead of a general acoustic finite element, and a viscous boundary was imposed on the outermost boundary. The validity and accuracy of the proposed method were secured by comparing analytic solutions of a reservoir having infinite domain, with the parametric analysis results, for the number of elements and the size of the modeling region. Furthermore, the proposed method was compared with other fluid-structure interaction methods using additional mass.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11a
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• pp.291-296
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• 2001

Recently, many methods are studied to analyze the noise of HDD and to reduce it. In this study, the simulation tool(SPATH) was developed to analyze a noise of HDD. The prediction technique of sound pressure level(SPL) of a given structural shape enables us to design a cover and a base with much less vibration and noise. In this paper, we measured the force of disk-spindle motor and predicted SPL from HDD by computational simulation. To get a SPL of HDD by computational simulation, modal analysis and forced vibration analysis were performed with ANSYS, and sound radiation was computed using SYSNOISE. The calculated results were compared with experimental results and a good agreement was obtained.

• Proceedings of the KSME Conference
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• 2001.06b
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• pp.210-215
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• 2001

CD-ROM Drives Rotating high speed as 10000 rpm cause serious noise and vibration problems. At the high speed, dominant noise is Air Borne Noise produced from high-speed airflow and Structure Borne Noise produced from structural vibration. In this research, vibration and sound characteristics in CD-ROM Drive were studied by the use of experimental analysis and computational simulation. Sound intensity techniques and ODS(Operational Deflection Shape) techniques are applied to identify the acoustic noise source of CD-ROM drive. And Computational simulation using SYSNOISE is conducted for describing the noise behavior.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.297-301
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• 2008

The flight vehicles have cavities such as wheel wells and bomb bays. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves. Resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. The flow field is observed to oscillate in the "shear layer mode" with low aspect ratio. In the present study, numerical analysis was performed for cavity flows by the unsteady compressible three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Wilcox's $\kappa$-$\omega$ turbulence model. The flow field is observed to oscillate in the shear layer mode" with large aspect ratio. Based on the SPL(Sound Pressure Level) analysis of the pressure variation at the cavity trailing edge, the dominant frequency was analyzed and compared with the results of Rossiter's formul. The aero-acoustic wave analyzed with CPD(Correlation of Pressure Distribution).