수치기법을 이용한 원심홴 소음의 음향학적 상사법칙 적용

전완호,이덕주 한국소음진동공학회 1999 소음 진동 Vol.9 No.5

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.

음향상사법을 이용한 멀티콥터형 소형무인기의 공력 소음 예측

이학진(Hakjin Lee),이덕주(Duck-Joo Lee) 한국소음진동공학회 2019 한국소음진동공학회 논문집 Vol.29 No.4

냉장고 내 냉기순환용 축류홴에 의한 내부 블레이드-통과-주파수 소음 예측

이승엽(Lee, Seung-Yub),허승(Heo, Seung),정철웅(Cheong, Cheol-Ung),김석로(Kim, Seok-Ro),서민영(Seo, Min-Young) 한국소음진동공학회 2009 한국소음진동공학회 논문집 Vol.19 No.5

Internal aeroacoustics of an axial fan used for circulating cold air in refrigerators are computed by using the hybrid method where CFD, acoustic analogy and BEM techniques are utilized. The unsteady flow field around the axial fan is predicted by solving the incompressible RANS equations with the conventional CFD techniques. Then, main noise sources are extracted from this unsteady flow field predictions using Acoustic Analogy. Lastly, BPF noise generated from an axial fan are predicted using these modeled sources combined with the tailed Green function techniques, which are numerically solved by the BEM technique. This hybrid model is validated by comparing the prediction with the experiment. Then, parameter studies are carried out, which suggest a capability of the current method as a design tool for the low-noise of the current axial fan system in a refrigerator.

음향상사기법을 이용한 터보프롭 중형항공기 소음원해석 및 객실 저소음 설계방안 연구

김민우,박영민,이해창 한국항공우주학회 2013 한국항공우주학회 학술발표회 논문집 Vol.2013 No.11

터보프롭항공기의 프로펠러 소음원을 해석하기 위하여 전산유체해석과 음향상사 기법과 연계한 소음해석 기법을 적용하였다. 비정상 프로펠러 유동해석 정보와 Farassat 1A 방정식을 이용 하여 해석을 수행하였다. 고도별, 순항속도별 조건에 따른 해석을 수행하여 동체에서 최고 소음도를 판별하고 BPF 주기에 따른 동체의 음향장 정보를 도시하였다. In this article, an acoustic analogy based noise prediction method is applied to noise sources of turboprop aircraft. For the noise analysis, unsteady CFD data and Farassat-1A equation are used for noise prediction. Noise predictions are carried out with various cruise conditions (altitude, cruise speed), and the numerical results show the maximum noise exposed regions and time-domain information on fuselage surface

펌프젯 추진기의 공동 비공동 유동소음에 대한 수치적 연구

구가람,정철웅,설한신,정홍석 한국음향학회 2023 韓國音響學會誌 Vol.42 No.3

In this study, the noise contributions by the duct, stator and rotor, which are the propulsor components, are evaluated to identify the flow noise source in cavitation and non-cavitation conditions on pumpjet propulsion and the noise levels in both conditions are compared. The unsteady incompressible Reynolds averaged Navier-Stokes (RANS) equation based on the homogeneous mixture assumption is applied on the suboff submarine hull and pumpjet propeller in the cavitation tunnel, and the Volume of Fluid (VOF) method and Schnerr-Sauer cavitation model are used to describe the two-phase flow. Based on the flow simulation results, the acoustic analogy formulated by Ffowcs Williams and Hawkings (FW-H) equation is applied to predict the underwater radiated noise. The noise contributions are evaluated by using the three types of impermeable integral surface on the duct, stator and rotor, and the two types of permeable integral surface surrounding the propulsor. As a result of noise prediction, the contribution by the stator is insignificant, but it affects the generation of flow noise source due to flow separation in the duct and rotor, and the noise is predominantly radiated into the upward and right where the flow separations are. Also, the noise is radiated into the thrust direction due to pressure fluctuation between suction and pressure sides on the rotor blades, and the it can be seen that the cavitation effect into the noise can be considered through the permeable integral surface. 본 연구에서는 펌프젯 추진기를 대상으로 공동, 비공동 조건에서의 유동 소음원을 규명하기 위하여 추진기의각 구성품인 덕트와 스테이터, 로터에 의한 소음 기여도를 평가하였으며, 공동과 비공동 조건에서의 소음 수준을 비교하였다. 대형 캐비테이션 터널 내 Suboff 잠수함 선형과 펌프젯 추진기를 대상으로 균일혼상류 가정의 비정상 비압축성 Reynolds averaged Navier-Stokes(RANS) 방정식을 적용하였으며, 이상 유동을 모사하기 위해 Volume of Fluid(VOF) 기법과 Schnerr-Sauer 공동 모델을 적용하였다. 유동해석 결과를 기반으로 수중방사소음을 예측하기 위해 Ffowcs Williams and Hawkings(FW-H) 방정식 기반의 음향상사법을 적용하였으며, 덕트와 스테이터, 로터로 구성된 3개의 비투과성 적분면과 추진기를 감싸는 형태의 2가지 투과성 적분면을 선정하여 소음 기여도를 평가하였다. 소음 예측결과로부터 스테이터는 전체 소음에 대한 직접적인 기여도는 낮으나 덕트와 로터에서의 유동 박리에 의한소음원 형성에는 영향을 미치는 것을 확인하였으며, 유동이 박리되는 연직상방과 우측방향으로 소음이 크게 방사되었다. 또한 로터에서는 날개의 흡입면과 압력면 간의 압력 섭동에 의해 추진방향으로 소음이 크게 방사되었으며, 투과성적분면을 통해 체적 소음원인 공동의 효과를 반영할 수 있음을 확인하였다

투과면을 이용한 고차의 유동소음 코드 개발

박민준(Min Jun Park),박수형(Soo Hyung Park),이학진(Hak Jin Lee),이덕주(Duck Joo Lee) 한국항공우주학회 2016 한국항공우주학회 학술발표회 논문집 Vol.2016 No.4

군용 및 민간 헬기에 대한 소음 규제로 인하여 헬기 설계에 있어서 저소음 로터 설계 기술이 필수적이다. 효과적으로 볼륨소음원에 의한 원거리 소음을 예측하기 위해 Ffowcs Williams and Hawkings 방적식에 Kirchhoff 접근법을 적용하여 볼륨 적분 없이 표면적분만으로 와류 소음을 예측할 있는 투과면 음향상사법을 개발하였다. 개발된 코드는 KFLOW의 고차 수치기법과 연계하여 UH-1H 제자리 비행에서의 High-Speed Impulsive 소음을 예측 및 검증하였다. 본 연구에서 개발된 전산유동소음코드를 통해 향후 다양한 조건에서의 유동과 소음이 연계된 해석이 가능할 것으로 기대된다. The rotor design with low noise is necessary as the noise can severely restrict the rotorcraft usage in both civilian and military operations. In order to predict efficiently the noise caused by volume noise sources in far-field, acoustic analogy code with permeable surface was developed as Kirchhoff approach was applied to Ffowcs Williams and Hawkings equation. Vortex noises can be predicted by using only surface integration of this manner without volume integration. High-Speed Impulsive noise of UH-1H in hover was predicted and validated using the developed code coupled with KFLOW with high-order scheme. This study anticipates that coupled analysis with fluid and noise can be possible in various conditions of rotorcraft through the developed acoustic code with KFLOW.

인공지능 기반 공력음향 이론 및 연구 동향

송지훈,김윤제 대한기계학회 2022 大韓機械學會論文集B Vol.46 No.9

Efforts to efficiently analyze flow-induced noise have been made for a long time, but slow development has been made due to the difficulty of theoretical identification due to complex interactions and the limitation of the high cost of experiments. Therefore, the basic theory and research trends of FSAI, and cases of AI applications and plans were presented in this study. Starting with Lighthill’s acoustic analogy, the theoretical approach was summarized Curle’s theory, and Ffowcs Williams and Hawkings equation. It is expected that the application of AI techniques, which have been rapidly developing in recent years, to aeroacoustics will supplement the limitations and suggest new problem solutions. 유동소음을 효과적으로 분석하려는 노력은 오랫동안 수행되었지만, 복잡한 상호작용으로 인한 이론적 규명의 어려움과 실험에 큰 비용이 소요된다는 한계로 더딘 발전이 이루어져 왔다. 이에, 본 연구에서는 유체-구조-음향 간의 상호작용을 분석하기 위해 공력음향학의 기초이론과 연구 동향, AI 적용사례 및 방안을 고찰하였다. 이론적 접근법은 Lighthill의 음향 상사법을 시작으로 Curle 음향이론, Ffowcs Williams와 Hawkings 방정식을 정리하였다. 최근 급격한 발전을 이루고 있는 AI 기법의 공력음향학에 대한 적용은 기존의 한계를 보완하고, 새로운 문제 해결법을 제시하리라 기대한다.

DES와 FW-H 음향상사법을 이용한 탠덤 실린더의 공력소음 특성 연구

김만식(Manshik Kim),이윤규(Youn Kyu Lee) 한국항공우주학회 2018 韓國航空宇宙學會誌 Vol.46 No.11

본 연구에서는 항공기 랜딩 기어와 유사한 형태의 탠덤 실린더에 대해 DES (Detached Eddy Simulation)와 FW-H(Ffowcs Williams and Hawkings) 음향상사법을 이용한 전산공력 소음해석을 수행하였다. 실린더 중심 간 거리 3.7D 조건에 대한 전산공력소음해석 결과를 탠덤 실린더를 지나는 외부 유동 특성 및 원거리 소음을 계측한 선행 연구 결과와 비교하였다. 전방 실린더의 상/하부에서 발생한 와류(Vortex)가 특징적인 주파수를 갖고 후방실린더에 충돌하면서 소음 발생원이 되는 것을 확인하였다. DES와 FW-H 음향상사법을 이용한 전산공력소음해석 방법의 타당성을 확인한 후, 전방 실린더의 후방에 분할판을 적용한 경우의 전산공력소음해석을 수행하였다. 전방 실린더의 후방에 분할판이 적용되면 전방실린더의 상/하부에서 발생하는 와류의 특징을 변화시키고 이극자 소음원 크기를 감소시켜 특정 주파수 대역에서 발생하는 소유 크기가 감소하는 것을 확인하였다. In this paper, aerodynamic noise simulation was conducted using DES (Detached Eddy Simulation) and FW-H (Ffowcs Williams and Hawkings) acoustic analogy for the tandem cylinders which have configuration similar to a landing gear of airplanes. Numerical simulation for the tandem cylinders whose centers are 3.7D apart was carried out and results were compared with the measured data such as flow characteristics, pressure coefficients on the cylinder surfaces and far-field noise characteristics. It was confirmed that periodically shedded vortices released at the upstream cylinder and impinged on the downstream cylinder surface are major sources of aerodynamic noise. After verifying the computational method of using DES and FW-H acoustic analogy for predicting aerodynamic noise of tandem cylinders, additional simulation was conducted to examine the effect of attaching a splitter plate at the rear of the upstream cylinder. It was confirmed that the noise level in specific frequency band decreased significantly because the splitter plate changed the vortex shedding features and reduced dipole noise source.

잠수함 형상의 유동소음 해석기법 연구

여상재,홍석윤,송지훈,권현웅,설한신 해양환경안전학회 2018 해양환경안전학회지 Vol.24 No.7

Underwater noise radiated from submarines is directly related to the probability of being detected by the sonar of an enemy vessel. Therefore, minimizing the noise of a submarine is essential for improving survival outcomes. For modern submarines, as the speed and size of a submarine increase and noise reduction technology is developed, interest in flow noise around the hull has been increasing. In this study, a noise analysis technique was developed to predict flow noise generated around a submarine shape considering the free surface effect. When a submarine is operated near a free surface, turbulence-induced noise due to the turbulence of the flow and bubble noise from breaking waves arise. First, to analyze the flow around a submarine, VOF-based incompressible two-phase flow analysis was performed to derive flow field data and the shape of the free surface around the submarine. Turbulence-induced noise was analyzed by applying permeable FW-H, which is an acoustic analogy technique. Bubble noise was derived through a noise model for breaking waves based on the turbulent kinetic energy distribution results obtained from the CFD results. The analysis method developed was verified by comparison with experimental results for a submarine model measured in a Large Cavitation Tunnel (LCT). 잠수함에서 발생하는 수중방사소음은 적함의 소나에 의해 피탐될 확률과 직결되며, 잠수함 저소음화 방안은 생존성 향상을 위해 필수적이다. 최신 잠수함의 경우 기계류 소음저감 및 고속/대형화가 진행됨에 따라 선체 주위에 발생하는 유동소음에 대한 관심이 높아지고 있다. 본 연구에서는 자유수면의 효과를 고려하여 잠수함 형상 주위에 발생하는 유동소음 수준을 예측할 수 있는 소음해석기법을 개발하였다. 잠수함이 자유수면 근처 운항시에 잠수함 주위 유동장의 교란에 의해 발생하는 난류유동소음과 쇄파버블에 의한 소음이 발생한다. 먼저 잠수함 주위 유동장 해석을 위해, VOF법 기반의 비압축성 이상유동(two-phase flow)해석을 수행하여 잠수함 주위 자유수면 형상과 유동장 정보를 도출하였다. 이후 난류유동소음해석을 위해 음향상사기법인 Permeable FW-H를 적용하였고, 쇄파버블 소음해석을 위해 유동해석에서 도출된 난류운동에너지 분포결과를 기반으로 쇄파버블 소음모델을 적용하였다. 최종적으로 개발된 유동소음 해석기법은 선박해양플랜트연구소(KRISO)의 대형캐비테이션터널(LCT)에서 수행된 잠수함 모형 유동소음계측 실험결과와 비교를 통해 검증을 수행하였다.

전산 소음 해석 기법을 이용한 잠수함 표면 처리에 따른 소음 효과 관찰

김승기(Seunggi Kim),유재영(Jaiyoung Ryu) 한국전산유체공학회 2021 한국전산유체공학회지 Vol.26 No.4

Submarine has been performed for national defense activities representatively as a multi-purpose underwater vehicle. Underwater Radiated Noise (URN) which emitted during underwater vehicle operation is directly related to the survivability of the underwater vehicle. This study focused on examining the effects of surface treatment on noise aspects in whole submarine body for the first time. Prior to the acoustic analysis on the submarine model, the acoustic analysis procedure using commercial CFD software was verified using a 2D cylinder model. Acoustic analysis on submarine model was conducted for two cases: smooth surface as a reference case, and a few micrometers of V-type applied riblet case. To solve the incompressible fluid flow passing the submarine, the Reynolds-averaged Navier-Stokes (RANS) equation coupled with the k-ω SST turbulence model was used. For acoustic analysis, the Ffowcs Williams and Hawkings acoustic analogy, which calculates flow-induced noise by designating a physical wall as a noise source, was used. The noise effects according to the surface treatment on submarine shape were examined by comparing overall sound pressure level (OASPL) between smooth and riblet case and the results indicate that noise around submarine shape was reduced about 4.3 dB in maximum on surface-treated area. However, when calculating OASPL excluding noise below 20 Hz, which is a frequency range where noise does not propagate, the noise tends to increased due to riblet shape. This study provides established procedure in acoustic analysis on whole submarine body and a new perspective that underwater radiation noise should be considered when designing surface treatment on submarine.