• 한국음향학회지
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• 제41권6호
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• pp.698-704
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• 2022

본 논문에서는 노즐 내부 유동의 소음원으로부터 발생되어 방사되는 공력 소음을 정량적으로 분석하였으며, 이를 외부 방사소음 결과와 비교하였다. 세가지 종류의 노즐 형상에 대해 내부 및 외부 유동을 정확히 예측하기 위해 고해상도 수치해석 기법인 비정상 압축성 대와류모사(Large Eddy Simulation, LES) 기법을 사용하였다. 와류소음원(Vortex Sound Source)을 통해 유동소음원을 확인하였으며, 이를 통해 노즐 내부 형상에서 주요 유동소음원의 분포를 확인하였다. 노즐 내부 유동의 와류소음원 레벨과 외부 방사 소음의 예측결과 및 측정결과와 비교하였으며, 이를 통해 정량적 분석을 검증하였다.

• 대한기계학회논문집A
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• 제21권6호
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• pp.942-950
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• 1997

Far field acoustic pressure from the evolution and interaction of three-dimensional vortex filament is calculated numerically. A vortex ring is a typical example of the three-dimensional vortex filament. An elliptic vortex ring emits a strong sound signal due to significant distortion and stretching of the vortec filament. The far field acoustic pressure is linearly dependent on the third time derivatives of the vortex positions. A numerical scheme of high resolution is employed to describe in detail the elliptic vortex ring motions which ar highly nonlinear. Descretized vortex filaments are interpolated by using a parametric blending function to remove a possible numerical instability. The distorted vortex filament, owing to the self-induced and the induced velocity from the other vortex segments, is redistributed at each time step. The accuracy and efficiency of the scheme are validated by comparisons with the analytic solution of circular vortex ring interaction.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 추계 학술대회논문집
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• pp.22-25
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• 2006

Direct simulations of aerodynamic sound, especially sound emitted by rapidly rotating elliptic cylinder by the finite difference lattice Boltzmann method (FDLBM). Effect of pile-fabrics for noise reduction is also studied by the finite volume LBM (FVLBM) using an unstructured grid. Second order time integration and third order upwind scheme are shown to be enough for these simulations. Sound sources are detected to be doublets for both cases. For the elliptic cylinder, the doublet is generated in the interaction between the vortex and the edge. For the circular cylinders, they are generated synchronizing with the Karman vortex street, and it is also shown that the pile-fabrics covering the surface of the cylinder reduces the strength of the source.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2000년도 춘계 학술대회논문집
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• pp.45-50
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• 2000

We study a conceptual numerical model on shock-vortex interaction setting an impulsive shock in a compressible vertex. Navier-Stokes equations are solved for the investigation of interactive structure and acoustic wave propagation. The rotationally symmetric vortex enforces two compression-expansion pairs resultantly forming a quadrupolar shape. These compressive and expansive waves cylindrically propagate to the far field and turn to acoustic waves. Using a fine uniform Cartesian grid system and a TVD-high resolution method, the flow data irl: precisely obtained to extend our interest to the sound source.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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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.

• 대한기계학회논문집B
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• 제26권9호
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• pp.1319-1324
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• 2002

A theoretical model on shock-vortex interaction is investigated using a numerical technique to solve Navier-Stokes equations. The shock-vortex interaction generated by this model based on the classical Rankin vortex is precisely investigated for a benchmark problem: Dosanjh and Weeks experiment. In terms of shock dynamics, the interaction is categorized to three stages: shock distortion, shock split, and shock-shock interaction. The quadrupolar structure of the sound source produced by the interaction is far supported with the present model, and the difference between experiment and theoretical model is also discussed in this paper.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.71-77
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• 2000

An axisymmetric supersonic jet is simulated at a Mach number of 1.5 and a Reynolds number of $10^5$ to identify the mechanism of sound radiation from the jet. The present simulation is performed based on the high-order accuracy and high-resolution ENO(Essentially Non-Oscillatory) schemes to capture the time-dependent flow structure representing the sound source. In this simulation, optimum expansion jet is selected as a target, where the pressure at nozzle exit is equal to that of the ambient pressure, to see pure shear layer growth without effect of change in jet cross section due to expansion or shock wave generated at nozzle exit. Shock waves are generated near vortex rings, and discernible pressure waves called Mach wave are radiated in the downstream direction with an angle from the jet axis, which is characteristic of high speed jet noise. Furthermore, vortex roll-up phenomena are observed through the visualization of vorticity contours.

• 대한기계학회논문집
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• 제18권3호
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• pp.584-590
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• 1994

A theoretical model has been developed to analyze the jet-edge interaction and the sound radiation. The edge responding to the sinuous impinging jet is regarded as an array of dipoles and their strength is determined by the boundary condition on the edge surface. The surface pressure distribution and the edgeforce are estimated using these dipoles. Then the pressure amplitude and directivity of the sound field is obtained by summing the radiating sounds from the dipole sources. It is found that the effective source is located a little distance downstream from the edge tip. And the directivity of the sound radiation is cardioid pattern near the edge but dipole pattern far from the edge. The theoretical model is confirmed by comparing the theoretical prediction of the edgeforce and sound pressure level with available experimental data.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 춘계학술대회 논문집
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• pp.504-507
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• 2009

The purpose of this work is to predict the low frequency aero-acoustic noise generated from the horizontal axis wind turbine, NREL Phase VI using large eddy simulation and Ffowcs-Williams and Hawkings model provided in the commercial code, FLUENT. Calculated aerodynamic performances such as shaft torque and power are compared with experimentally measured value. Performance results show a good agreement with experimental data within about 0.8%. If the distance by two times is changed from 32D to 64D toward the downstream region, sound pressure level is reduced by about 6.4dB.

• 한국항공우주학회지
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• 제30권1호
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• pp.28-35
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• 2002

공동흐름에서 직각 계단은 커다란 소음의 원인이 되어 많은 사람들의 와류와 직각계단의 상호 작용 시에 발생되는 소음의 저감 방안을 연구하여 왔다. 본 연구에서는 2차원 저아음속 와류 흐름이 전향계단을 지날 때 발생되는 유동 소음을 전향계단의 형상 변화를 통한, 즉, 계단의 모따기 양과 각도를 바꾸어 가면서 수치적으로 계산하였다. 내부 유동장을 구하기 위해서 비압축성 비점성 이산와류 모델을 가정하였으며, 유동정보로부터 원거리로의 음향장 계산은 MAE 이론을 적용하여 구하였다. 음원에서의 음압과 음압강도를 모따기 높이 및 모따기 각도와 최기 와류의 높이를 변화시켜가면서 다양하게 수치적인 결과를 얻어내었다. 본 연구를 통해서 계단에 접근하는 와류에 의한 원거리 음압은 모따기 양이 계단 높이의 30%에서 모따기 각도가 $15^{\circ}C$에서 $30^{\circ}C$°사이일 때 가장 소음이 적게 발생되는 결과를 얻어내었다.