• The Journal of the Acoustical Society of Korea
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• v.39 no.6
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• pp.515-523
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• 2020

This study aims to improve the flow and noise performances of an axial-flow fan for cooling the machine room in a refrigerator by using airfoil-cascade analysis and surface ridge shape. First, the experimental evaluations using a fan performance tester and an anechoic chamber are performed to analyze the flow and noise performances of the existing fan system. Then, the corresponding flow and noise performances are numerically assessed using the Computational Fluid Dynamics (CFD) techniques and the Ffowcs-Williams and Hawkings (FW-H) equation, and the validity of numerical results are confirmed through their comparisons with the experimental results. The analysis for the flow of a cascade of airfoils constructed from the existing fan blades is performed, and the pitch angles for the maximum lift-to-drag ratio are determined. The improved flow performance of the new fan applied with the optimum pitch angles is confirmed. Then, the fan blades with surface ridges on their pressure sides are devised, and the reduction of aerodynamic noise of the ridged fan is numerically confirmed. Finally, the prototype of the final fan model is manufactured, and improvements in the flow and noise performances of the prototype are experimentally confirmed.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.4
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• pp.92-102
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• 2012

The process of the wind noise analysis around an OSRVM is developed and is verified by simulating unsteady flow field past a generic OSRVM mounted on the flat plate at the Reynolds number of $Re_D=5.2{\times}10^5$ based on the mirror diameter. The transient flow field past a generic OSRVM is simulated with various turbulence models, namely DES-SA, LES Constant SGS, and LES Dynamic SGS. The sound radiation is predicted using the Ffowcs- Williams and Hawkings analogy. For the present simulation, the 6.35million cells are generated. Time averaged pressure coefficients at 34 locations on the surface of the generic OSRVM are compared with the available experimental data. Also, 12 Sound Pressure Levels located on the surrounding mirror are compared with the available experimental data. Both of them show good agreements with experimental data.

• The Journal of the Acoustical Society of Korea
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• v.37 no.6
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• pp.396-403
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• 2018

In this paper, a high-performance and low-noise centrifugal fan is developed for cooling automotive seats which provide a driver with pleasant driving environment. First, the flow characteristics of the existing fan unit was analyzed using a fan performance tester and CFD (Computational Fluid Dynamics) simulations. The analysis of the predicted flow field indicated vortex flow near the tip of fan hub and stagnation flow on the top of fan hub. Two design points are devised to reduce the vortex flow and the stagnation flow observed in the existing fan unit. First, the cut-off clearance which is the minimum distance between the fan blade and the fan housing is increased to reduce the vortex strength and, as a result, to reduce the overall sound pressure level. Second, the hub shape is more modified to eliminate the stagnation flow. The validity of proposed design is confirmed through the numerical analysis. Finally, a prototype is manufactured with a basis on the numerical analysis result and its improved flow and noise performances are confirmed through the P-Q curves measured by using the Fan Tester and the SPL (Sound Pressure Level) levels measured in the anechoic chamber.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.6
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• pp.765-771
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• 2019

With the increase in the speed of ships and the size of ocean structures, the importance of flow noise has become increasingly critical in meeting regulatory standards. However, unlike active investigations in aeroacoustics fields for airplanes and trains, which are based on acoustic analogy methods for tonal and broadband frequency noise, only the discrete blade passing frequency noise from propellers is considered in marine fields. In this study, prediction methods for broadband noise in marine propellers and underwater appendages are investigated using FW-H Formulation1B, which can consider the mechanism of primary noise generation of trailing edge noise. The original FW-H Formulation 1B is based on the pressure correlation function tolackitsgeneralityandaccuracy. To overcome these limitations, wall-pressure spectrum models are adopted to improve the generality in fluid mediums. The comparison of the experimental results obtained in air reveals that the proposed model exhibits a higher accuracy within 5 dB. Furthermore, the prediction procedures for broadband noise for hydrofoils are established, and the estimation of broadband noise is conducted based on the results of the computational fluid dynamics.

• The Journal of the Acoustical Society of Korea
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• v.37 no.5
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• pp.263-270
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• 2018

In most industry fields concerning external flow noise problems, the hybrid computational aeroacoustic techniques based on the FW-H (Ffowcs Williams and Hawkings) equation are widely used for its numerical efficiency. However, when the surface integral form of FW-H equation is used without volume quadrupole sources, it is known to generate significant non-physical noise in a certain case. Especially, in the case of a flow in which the tip vortex cavitation is formed in the distant downstream direction such as flow driven by an underwater propeller, the accuracy in noise prediction becomes poor unless it is not properly modelled. Therefore, in this study, the nonphysical acoustic waves caused by the surface integral form of FW-H equation is reduced by adding the quadrupole correction term. First, to verify the accuracy of the in-house code of FW-H equation, the noise by an axial fan used in the outdoor unit of air conditioner was calculated and compared with the results of ANSYS Fluent. In order to verify the effects of the quadrupole correction term, the noise prediction for isentropic vortex convection is performed and it is confirmed that the error is reduced by the quadrupole correction term. Finally, the noise prediction is performed for the flow field generated by the Clark-Y hydrofoil in underwater. It is confirmed that the error caused by the cavitation passing through the integral surface can be reduced by the quadrupole correction term.