• The Journal of the Acoustical Society of Korea
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• v.43 no.1
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• pp.103-111
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• 2024

Axial-flow fans are used to transport fluids in relatively low-pressure flow regimes, and a variety of design variables are employed. The tip geometry of an axial fan plays a dominant role in its flow and noise performance, and two of the most prominent flow phenomena are the tip vortex and the tip leakage vortex that occur at the tip of the blade. Various studies have been conducted to control these three-dimensional flow structures, and winglet geometries have been developed in the aircraft field to suppress wingtip vortices and increase efficiency. In this study, a numerical and experimental study was conducted to analyze the effect of winglet geometry applied to an axial fan blade for an air conditioner outdoor unit. The unsteady Reynolds-Averaged Navier-Stokes (RANS) equation and the FfocwsWilliams and Hawkings (FW-H) equation were numerically solved based on computational fluid dynamics techniques to analyze the three-dimensional flow structure and flow noise numerically, and the validity of the numerical method was verified by comparison with experimental results. The differences in the formation of tip vortex and tip leakage vortex depending on the winglet geometry were compared through a three-dimensional flow field, and the resulting aerodynamic performance was quantitatively compared. In addition, the effect of winglet geometry on flow noise was evaluated by numerically simulating noise based on the predicted flow field. A prototype of the target fan model was built, and flow and noise experiments were conducted to evaluate the actual performance quantitatively.

• Journal of the Korea Convergence Society
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• v.12 no.2
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• pp.215-219
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• 2021

The flow analyses around the wing of airplane installed with winglet or sharkelt were carried out in this study. At the model without winglet, it can be seen that the air flows beside the wing and the flow is concentrated at the end of wing. At the model of winglet or sharklet, the pressure on the bottom of the wing happens to be lower in the wide area than for model without winglet. At the analysis result, the air flowing next to the wing can be seen to go over and rotates over the main wing. The model with the sharklet shows that the flow rate is the fastest. In case of model with sharklet, it is thought that the maximum total pressure of flow is distributed at the bottom of the wing, which can further improve the lift force of the wing. It is thought that the analysis results in this study on the air flow due to the configuration of aircraft edge wing can be helped at its convergent research.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.1
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• pp.37-46
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• 1999

The influence of the tip clearance upon the cavitation inception were investigated by experiments for ducted rotors having different tip clearances The axial and tangential mean velocities around the ducted rotors were measured using an L.D.V. system to investigate the correlation between tip vertex cavitation inception and hub vortex cavitation. Observation results for tip vortex cavitation and hub vortex cavitation show good agreement in trend with the analysis results of velocity measurement. An optimum tip clearance for ducted rotor was selected to delay the tip vortex cavitation.

• The Journal of the Acoustical Society of Korea
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• v.39 no.2
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• pp.77-86
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• 2020

In this study, the Eulerian/Lagrangian one-way coupling method is proposed to predict flow noise due to Blade-Tip Vortex Cavitation (BTVC). The proposed method consists of four sequential steps: flow field simulation using Computational Fluid Dynamics (CFD) techniques, reconstruction of wing-tip vortex using vortex model, generation of BTVC using bubble dynamics model and acoustic wave prediction using the acoustic analogy. Because the CFD prediction of tip vortex structure generally suffers from severe under-prediction of its strength along the steamwise direction due to the intrinsic numerical damping of CFD schemes and excessive turbulence intensity, the wing-tip vortex along the freestream direction is regenerated by using the vortex modeling. Then, the bubble dynamics model based on the Rayleigh-Plesset equation was employed to simulate the generation and variation of BTVC. Finally, the flow noise due to BTVC is predicted by modeling each of spherical bubbles as a monople source whose strength is proportional to the rate of time-variation of bubble volume. The validity of the proposed numerical methods is confirmed by comparing the predicted results with the measured data.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.4
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• pp.289-296
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• 2011

In this study, fairing configurations for an aircraft are designed and the aerodynamic analyses of the fairings are performed to find the best choice for the aircraft. Fairings considered are wing-tip fairing and wing-body fairing. Wing alone analyses are done for the wing-tip faring selection, while wing-body-tail analyses are done for the wing-body fairing selection. A 3-D RANS solver with Menter's ${\kappa}-{\omega}$ SST turbulence model are used for the aerodynamic analyses. The effects on the drag of the aircraft are examined by comparing the analysis results with and without the farings.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.1
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• pp.94-103
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• 1993

This study deals with an investigation on the tip vortex generated by an elliptic wing with section shapes of NACA 0020. The flow structure on the wing surface is investigated by using tufts test as well as observing the cavitation pattern. The surface pressure on a foil surface is measured to complement the visualized flow field. Results show that a strong spanwise pressure gradient is a definite contributor on the formation of tip vorex, and the fluids from both sides contribute to the evolutionary process of tip vortex. On the other hand, a series of experiments are conducted to investigate the detailed structure of tip-vortex at various angles of attack. The tip-vortex formation and development are observed by producing a cavitation, and then by a laser sheet technique in conduction with a dye injection method. The shape of tip-vortex and the distance between a vortex core and the trailing vortex sheet are found to vary with the angle of attack. Overall features of tip flow are evaluated to complement the vortex model based on inviscid theory.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.9
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• pp.753-760
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• 2007

In a 3-D flapping motion, the spanwise flow is generated while the wing is moved on the stroke plane. And at the end of each stroke, the rotational circulation is generated due to a wing rotation. In this study, to evaluate the effect of spanwise flow and wing rotation on the aerodynamic characteristics in 3-D flap 753ping motion, a 3-D flapping motion was compared with a 2-D translating motion. In each flapping motion, the aerodynamic forces were measured with respect to the angles of attack and Reynolds number. The aerodynamic forces generated by 2-D translating motion were higher than those generated by 3-D flapping motion. While the lift of 3-D flapping motion was increased until the angle of attack $60^{\circ}$ at mid-stroke, the lift generated by 2-D translating motion was decreased above the angle of attack 40° at mid stroke. Also, at the end of each stroke, the aerodynamic forces were increased rapidly due to wing rotation.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.167-170
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• 2004

본 논문에서는 수중익 버블 캐비테이션과 날개 끝 볼텍스 캐비테이션의 거동 및 소음을 Eulerian-Lagrangian 기법을 이용하여 수치적으로 해석하였다. Eulerian-Lagrangian 기법은 캐비테이션 버블이 유동장에 미치는 영향이 거의 없다는 가정하에 유동장과 캐비테이션 거동을 일방으로 연계하여 해석하는 방식이다. 수중익 버블 캐비테이션 해석을 위한 유동장은 비압축성 RAMS 방정식을 해석하여 구하고 날개 끝 볼텍스 캐비테이션 유동장은 일반적 CFD 기법의 큰 수치 소산으로 그 특성이 잘 나타나지 않으므로 Sculley 볼텍스 모델을 이용하여 해석한다. 해석한 유동장 정보를 입력치로 하고 버블의 지배 방정식인 Rayleigh-Plesset 방정식과 Newton의 제2법칙에 근거한 궤적 방정식을 연계하여 캐비테이션의 성장-붕괴와 운동을 예측한다. 계산된 거동 정보를 이용하여 버블 캐비테이션과 날개 끝 볼텍스 캐비테이션의 소음을 예측하였다. 본 연구는 수중 운동체에서 발생하는 캐비테이션의 거동과 소음의 특성을 파악하고 그에 따른 대비책을 마련하는 기본 연구로서 활용할 수 있을 것이다.

• The Journal of the Acoustical Society of Korea
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• v.40 no.4
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• pp.261-269
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• 2021

Without any validation of the incompressible assumption, most of previous studies on cavitation flow and its noise have utilized numerical methods based on the incompressible Reynolds Average Navier-Stokes (RANS) equations because of advantage of its efficiency. In this study, to investigate the effects of the flow compressibility on the Tip Vortex Cavitation (TVC) flow and noise, both the incompressible and compressible simulations are performed to simulate the TVC flow, and the Ffowcs Williams and Hawkings (FW-H) integral equation is utilized to predict the TVC noise. The DARPA Suboff submarine body with an underwater propeller of a skew angle of 17 degree is targeted to account for the effects of upstream disturbance. The computation domain is set to be same as the test-section of the large cavitation tunnel in Korea Research Institute of Ships and Ocean Engineering to compare the prediction results with the measured ones. To predict the TVC accurately, the Delayed Detached Eddy Simulation (DDES) technique is used in combination with the adaptive grid techniques. The acoustic spectrum obtained using the compressible flow solver shows closer agreement with the measured one.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.6
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• pp.501-508
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• 2011

In order to control the tip vortex cavitation occurring around the tip of a rotating propeller blade, researches on the propeller cavitation and blade tip vortex flows have been increased. In this paper, the propeller tip vortex flow for a blunt and sharp tips was studied using an unsteady Reynolds-averaged Navier-Stokes equations solver based on a cell-centered finite volume method. In numerical open water test, torques, thrusts, pressure distributions and vortex flows were compared for various rotating speeds. To consider a hull wake, the nominal wake was specified in inlet boundary condition. Pressure distributions and vortex flows with the hull wake were investigated for various propeller rotating angles. From the results, it was confirmed that the blunt tip propeller delayed the tip vortex flow.