• Journal of the Korean Society of Marine Environment & Safety
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• v.20 no.6
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• pp.752-759
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• 2014

Varieties of research on turbulent-induced noise is conducted with combinations of acoustic analogy methods and computational fluid dynamic methods to analyze efficiently and accurately. Application of FW-H acoustic analogy without turbulent noise is the most popular method due to its calculation cost. In this paper, turbulent-induced noise is predicted using RANS turbulence model and permeable FW-H method. For simplicity, noise from 2D cylinder is examined using three different methods, direct method of RANS, FW-H method without turbulent noise and permeable FW-H method which can take into account of turbulent-induced noise. Turbulent noise was well predicted using permeable FW-H method with same computational cost of original FW-H method. Also, ability of permeable FW-H method to predict highly accurate turbulent-induced noise by applying adequate permeable surface is presented. The procedure to predict turbulent-induced noise using permeable FW-H is established and its usability is shown.

• The Journal of the Acoustical Society of Korea
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• v.37 no.2
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• pp.83-91
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• 2018

The noise sources of a tip-jet driven rotor can be separated by rotor blade noise and jet noise. The rotor blade noise consists of thickness noise, loading noise, nonlinear quadrupole noise, and jet noise is divided into nozzle momentum noise and jet radiation noise. The flow analysis for the prediction of rotor blade noise is performed by CFD (Computational Fluid Dynamics) analysis, and the noise source of the rotor blade noise is identified by simultaneously applying the permeable and impermeable surface based FW-H (Ffowcs Williams-Hawkings) acoustic analogy. The nozzle momentum noise is obtained by permeable surface FW-H, and jet radiation noise is predicted by using empirical method for the fixed-wing jet. Both of jet noises use nozzle exit condition for noise analysis. The accuracy of the technique is verified based on the noise measurements of the tip-jet driven rotor, and the unique noise characteristics of the tip-jet driven rotor is confirmed by spectrum analysis.

• Journal of KSNVE
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• v.9 no.5
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• pp.955-965
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• 1999

Centrifugal fans are widely used and the noise generated by the these machines causes one of the most serious problems. In general, the centrifugal fan noise is often dominated by tones at BPF(blade passage frequency) and its higher harmonics. This is a consequence of the strong interaction between the flow discharged form the impeller and the cutoff in the casing. However, only a few researches have been carried out on predicting the noise because of the difficulty in obtaining detailed information about the flow field and casing effects on noise radiation. The objective of this study is to understand the generation mechanism of sound and to develop a prediction method for the unsteady flow field and the acoustic pressure field of a centrifugal fan. We assume that the impeller rotates with a constant angular velocity and the flow field of the impeller is incompressible and inviscid. So, a discrete vortex method (DVM) is used to model the centrifugal by the unsteady Bernoulli equation. Lowson's method is used to predict the acoustic source. A centrifugal impeller and wedge introduced by Weidemann are used in the numerical calculation and the results are compared with the experimental data. Reasonable results are obtained not only for the peak frequencies but also for the amplitudes of the tonal sound.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.447-450
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• 2004

선박에서 발생하는 소음 가운데 수중 추진기 소음은 가장 우세한 소음이다. 추진기 소음은 소나에 의해 적을 탐지하는 군용 선박에 경우 생존과 직결된 문제가 되며 쾌적함과 정숙성을 요구하는 여객선의 경우에서도 중요한 문제로 대두되고 있다. 이러한 중요성과 필요성에 따라, 본 연구에서는 수중 추진기의 비공동 및 공동 소음을 수치적으로 해석하였다. 수중 추진기 소음 해석을 위해 유동 해석이 선행되어야 하며 이는 포텐셜을 기반으로 한 패널법을 이용하여 해석한다. 소음 해석은 시간 영역 음향상사법을 이용하였으며, 공동 소음은 홀극 음원으로 모사하여 해석하였다. 또한 향후 수중 추진기의 날개 끝 볼텍스 캐비테이션 해석을 위한 기초연구로서 Eulerian-Lagrangian 접근법을 이용하여 수중익에서의 날개 끝 볼텍스 캐비테이션의 거동과 소음을 예측하였다.

• 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.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.04a
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• pp.196-201
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• 1995

The broadband and discrete sources of sound in small cooling fans of propeller type and centrifugal type were investigated to understand the turbulent vortex structures from many bladed fans using ANSI test plenum for small air-moving devices (AMDs). The noise measurement method uses the plenum as a test apparatus to determine the acoustic source spectral density function at each operating conditions similar to real engineering applications based on acoustic similarity laws. The characteristics of fans including the head rise vs. volumetric flow rate performance were measured using a performance test facility. The sound power spectrum is decomposed into two non-dimensional functions: an acoustic source spectral distribution function F(St,.phi.) and an acoustic system response function G(He,.phi.) where St, He, and .phi. are the Strouhal number, the Helmholtz number, and the volumetric flow rate coefficient, respectively. The autospectra of radiated noise measurements for the fan operating at several volumetric flow rates,.phi., are analyzed using acoustical similarity. The rotating stall in the small propeller fan with a bell-mouth guided is mainly due to a leading edge separation. It creates a blockage in the passage and the reduction in the flow rate. The sound power levels with respect to the rotational speeds were measured to reveal the mechanisms of stall and/or surge for different loading conditions and geometries, for example, fans installed with a impinging plate. Lee and Meecham (1993) studied the effect of the large-scale motions like impinging normally on a flat plate using Large-Eddy Simulation(LES) and Lighthill's analogy.[ASME Winter Annual Meeting 1993, 93-WA/NCA-22]. The dipole and quadrupole sources in the fans tested are shown closely related to the vortex structures involved using cross-correlations of the hot-wire and microphone signals.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.421-426
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• 1999

수중 프로펠러의 비공동 소음을 Ffowcs William-Hawkings 형태의 음향 상사 방정식을 시간영역에서 해석하였으며 전산공력음향학(CAA)과 경계 요소법(BIEM)등 수치적 방법을 통해 해석하였다. 덕트 없는 프로펠러와 덕트 프로펠러에 대해서 비균일 유입류 조건에 대해서 소음 강도와 방향성을 예측하였으며 이는 수중 프로펠러의 운용시 지배적인 소음원을 구별하고 그 특성을 파악하여 적절한 소음 제어 책을 마련하는 기반이 될 것이다.

• Proceedings of the Acoustical Society of Korea Conference
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• 1998.06c
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• pp.461-464
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• 1998

수중 프로펠러의 비공동 소음을 수치적으로 해석하였다. Ffowcs Williams-Hawkings 형태의 음향상사 방정식을 시간영역에서 해석하였으며 임의의 형상과 하중조건을 가지는 프로펠러의 소음 예측이 가능하도록 하였다. 또한 좌표계 변환을 통해 관찰자에 대해 상대적 운동이 있는 경우에도 소음 예측이 가능하도록 하였다. 균일/비균일 유입류 조건을 갖는 수중 프로펠러에 대해 소음 해석을 수행하였고 각각의 조건에 대해 음원별 소음 강도와 방향성을 예측하였다. 수치 해석결과 프로펠러 표면상의 압력 변화에 따른 비정상 하중에 의한 이중극 소음이 지배적인 것으로 나타났다. 이러한 음원별 접근법은 수중 프로펠러의 운용시 지배적인 소음원을 구별하고 그 특성을 파악하여 적절한 소음 제어책을 마련하는 기반이 될 것이다.

• The Journal of the Acoustical Society of Korea
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• v.33 no.3
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• pp.153-162
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• 2014

Empirical prediction method of the acoustic load on the fairing is based on jet experimental data on the basis of similarity principle. Representative empirical prediction method, DSM-II(Distributed Source Method-II), is a distributing source method along the jet plume. But the empirical prediction model is limited to reflect the impingement source in real environment because it is based on the free jet data. So, we propose a empirical prediction method considering the impinging jet effect by adding a impingement source in the existing prediction method. Considering the additional source's displacement, spectrum, strength and directivity, we calculate the acoustic load on the KSR-III(Korean Sounding Rocket-III) rocket and compare the results with the existing method and experiment data.

• Journal of KSNVE
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• v.6 no.6
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• pp.755-762
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• 1996

An acoustic transmission loss analysis method for mufflers with complex geometry is developed using MSC/NASTRAN on the basis of acoustic-structural analogy and two-microphone method. In this study, mufflers with simple and complex shapes are analyzed using this method and compared with theoretical and experimental results to verify it. Applying this method to design of discharge muffler in a rotary compressor, we obtained 2dB(A) of noise reduction in the range of lower than 1300Hz. Futhermore, adopting this technique for a suction muffler in reciprocal compressor, more than 10dB(A) noise reduction at 500Hz, and in total, 3dB(A) noise reduction is achieved.