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오일러 방정식과 자유 후류법을 이용한 헬리콥터 로터의 비정상 공력 해석 연구
이재훈(Jaehun Lee),위성용(Seongyong Wie),권장혁(JangHyuk Kwon),이덕주(Duckjoo Lee),김대희(Dahee Kim) 한국전산유체공학회 2007 한국전산유체공학회 학술대회논문집 Vol.2007 No.-
In this study the unsteady aerodynamic analysis of a hovering helicopter rotor is performed For the accurate flow field analysis Euler equations and the free wake method are coupled The Euler equations are solved to find the pressure distribution around the rotor, and free wake method is used to give the boundary condition for the solution of Euler equations. Also, vortex strength and wake motion after the rotor are simulated by the free wake method The accuracy of the present method is compared with the source sink model. The present method is applied to the hovering Caradonna-Tung rotor and compared with experimental results.
Noise Prediction of Ducted Fan Unmanned Aerial Vehicles considering Strut Effect in Hover
Minjun Park,Jisung Jang,Duckjoo Lee 한국항공우주학회 2017 International Journal of Aeronautical and Space Sc Vol.18 No.1
In recent years, unmanned aerial vehicles (UAVs) have been developed and studied for various applications, including drone deliveries, broadcasting, scouting, crop dusting, and firefighting. To enable the wide use of UAVs, their exact aeroacoustic characteristics must be assessed. In this study, a noise prediction method for a ducted fan UAV with complicated geometry was developed. In general, calculation efficiency is increased by simulating a ducted fan UAV without the struts that fix the fuselage to the ducts. However, numerical predictions of noise and aerodynamics differ according to whether struts are present. In terms of aerodynamic performance, the total thrust with and without struts is similar owing to the tendency of the thrust of a blade to offset the drag of the struts. However, in aeroacoustic simulations, the strut effect should be considered in order to predict the UAV’s noise because noise from the blades can be changed by the strut effect. Modelling of the strut effect revealed that the dominant tonal noises were closely correlated with the blade passage frequency of the experimental results. Based on the successful detection of noise sources from a ducted fan UAV system, using the proposed noise contribution contour, methods for noise reduction can be suggested by comparing numerical results with measured noise profiles.
김용석(Yongseok Kim),이덕주(Duckjoo Lee) 한국항공우주학회 2007 韓國航空宇宙學會誌 Vol.35 No.2
초음속 제트 마하수 1.07부터 1.2 범위에서 축대칭 제트 스크리치 톤을 해석하였다. 축대칭 모드는 낮은 마하수 축대칭 제트의 지배적인 스크리치 톤 모드이다. 난류 해석을 위해 수정된 Spalart-Allmaras 모델을 RANS (Reynolds-averaged Navier-Stokes) 방정식에 사용하였다. 스크리치 톤 해석에서 중요한 음파의 전파, shock-cell 구조 및 거대한 불안정 파를 정확히 계산하기 위해 비반사 특성 경계조건과 연계한 고차정확도의 ENO 기법을 사용하였다. 수치 해석결과는 다른 연구자들의 실험 및 계산 결과와 잘 일치하였으며, 따라서 본 연구에 사용된 수치 기법들이 초음속 제트 유통 및 소음연구에 타당함을 확인하였다. An axisymmetric supersonic jet screech in the Mach number range from 1.07 to 1.2 is numerically simulated. The axisymmetric mode is the dominant screech mode for an axisymmetric jet. The Reynolds-averaged Navier-Stokes equations in the conjunction with a modified Spalart-Allmaras turbulence model are employed. A high resolution finite volume essentially non-oscillatory(ENO) schemes are used along with nonreflecting characteristic boundary conditions that are crucial to screech tone computations to accurately capture the sound waves, shock-cell structures and large-scale instability waves.
Noise Prediction of Ducted Fan Unmanned Aerial Vehicles considering Strut Effect in Hover
Park, Minjun,Jang, Jisung,Lee, Duckjoo The Korean Society for Aeronautical and Space Scie 2017 International Journal of Aeronautical and Space Sc Vol.18 No.1
In recent years, unmanned aerial vehicles (UAVs) have been developed and studied for various applications, including drone deliveries, broadcasting, scouting, crop dusting, and firefighting. To enable the wide use of UAVs, their exact aeroacoustic characteristics must be assessed. In this study, a noise prediction method for a ducted fan UAV with complicated geometry was developed. In general, calculation efficiency is increased by simulating a ducted fan UAV without the struts that fix the fuselage to the ducts. However, numerical predictions of noise and aerodynamics differ according to whether struts are present. In terms of aerodynamic performance, the total thrust with and without struts is similar owing to the tendency of the thrust of a blade to offset the drag of the struts. However, in aeroacoustic simulations, the strut effect should be considered in order to predict the UAV's noise because noise from the blades can be changed by the strut effect. Modelling of the strut effect revealed that the dominant tonal noises were closely correlated with the blade passage frequency of the experimental results. Based on the successful detection of noise sources from a ducted fan UAV system, using the proposed noise contribution contour, methods for noise reduction can be suggested by comparing numerical results with measured noise profiles.
Numerical Investigation on a Rotor Tip-Vortex Instability in Very Low Advance Ratio Flight
Kihoon Chung,Changjeon Hwang,Duckjoo Lee,Jongbong Yim 한국항공우주학회 2005 International Journal of Aeronautical and Space Sc Vol.6 No.2
Helical tip vortex is known as stable vortex structure, however the specific frequency component of far wake perturbation induces the vortex pairing in hover and axial flight. It is expected that the tip vortex pairing phenomena may happen in transition flight and very low advance ratio flight so that inflow may be most nonuniform in the low advance ratio flight. The objectives of this paper are that a tip-vortex instability during the transition from hover into very low advance ratio forward flight is numerically predicted to understand a physics by using a time-marching free-wake method. To achieve the objectives, numerical method is firstly validated in typical axial and forward flights cases. Present scheme with trim routine can predict airloads and inflow distribution of forward flight with good accuracy. Then, the transition flight condition is calculated. The rotor used in this wake calculation is a small-scale AH-1G model. By using a tip-vortex trajectory tracking method, the tip-vortex pairing process are clearly observed in transient flight(μ=0.03) and disappears at a slightly higher advance ratio(μ=0.05). According to the steady flight simulation at μ=0.03, it is confirmed the tip-vortex pairing process is continued in the rear part of rotor disk and not occurs in the front part. Time averaged inflow in this case is predicted as smooth distribution.
Feasibility of Indium Tin Oxide (ITO) Swarf Particles to Transparent Conductive Oxide (TCO)
Sung-Jei Hong,DuckJoo Yang,Seung Jae Cha,Jae-Yong Lee,Jeong-In Han 한국태양광발전학회 2015 Current Photovoltaic Research Vol.3 No.2
Indium (In) is widely used for transparent electrodes of photovoltaics as a form of indium tin oxide (ITO) due to its superior characteristics of environmental stability, relatively low electrical resistivity and high transparency to visible light. However, In has been worn off in proportion to growth the In related market, and it leads to raise of price. Although In is obtained from ITO target scarps, much harmful elements are used for the recycling process. To decrease of harmful elements, ITO swarf particles obtained from target scraps was characterized whether it is feasible to transparent conductive oxide (TCO). The ITO swarf was crushed with milling process, and it was mixed with new ITO nanoparticles. The mixed particles were well dispersed into ink solvent to make-up an ink, and it was well coated onto glass substrate. After heat-treatment at 400°C under N₂ rich environments, optical transmittance at 550 nm and sheet resistance of the ITO ink coated layer was 71.6% and 524.67Ω/□, respectively. Therefore, it was concluded that the ITO swarf was feasible to TCO of touch screen panel.
Feasibility of Indium Tin Oxide (ITO) Swarf Particles to Transparent Conductive Oxide (TCO)
Hong, Sung-Jei,Yang, DuckJoo,Cha, Seung Jae,Lee, Jae-Yong,Han, Jeong-In Korea Photovoltaic Society 2015 Current Photovoltaic Research Vol.3 No.2
Indium (In) is widely used for transparent electrodes of photovoltaics as a form of indium tin oxide (ITO) due to its superior characteristics of environmental stability, relatively low electrical resistivity and high transparency to visible light. However, In has been worn off in proportion to growth the In related market, and it leads to raise of price. Although In is obtained from ITO target scarps, much harmful elements are used for the recycling process. To decrease of harmful elements, ITO swarf particles obtained from target scraps was characterized whether it is feasible to transparent conductive oxide (TCO). The ITO swarf was crushed with milling process, and it was mixed with new ITO nanoparticles. The mixed particles were well dispersed into ink solvent to make-up an ink, and it was well coated onto glass substrate. After heat-treatment at $400^{\circ}C$ under $N_2$ rich environments, optical transmittance at 550 nm and sheet resistance of the ITO ink coated layer was 71.6% and $524.67{\Omega}/{\square}$, respectively. Therefore, it was concluded that the ITO swarf was feasible to TCO of touch screen panel.
Kihoon Chung,Kwanjung Yee,Changjeon Hwang,Duckjoo Lee 한국항공우주학회 2004 International Journal of Aeronautical and Space Sc Vol.5 No.2
CFD method has been coupled with a time-marching free-wake model by using field velocity approach suggested by J. D. Baeder (Ref. 1). The coupled method has been applied to rectangular and BERP-like blades and the calculated performance data are compared with the experimental results. For hovering analysis, the present method could yield sufficiently good results with reasonable computation time and is particularly suitable for the flow field analysis with the complex shaped blade.
황경훈,이해준,고건,김석균,선용한,최덕주,Hwang, Kyung Hoon,Lee, Haejun,Koh, Geon,Kim, Seog Gyun,Sun, Yong Han,Choi, Duckjoo 대한의용생체공학회 2015 의공학회지 Vol.36 No.3
An effective image retrieval system is required as the amount of medical imaging data is increasing recently. Authors reviewed the recent development of text-based medical image retrieval including the use of controlled vocabularies - RadLex (Radiology Lexicon), FMA (Foundational Model of Anatomy), etc - natural language processing, semantic ontology, and image annotation and markup.