Time Accurate Finite Difference Method for Performance Prediction of a Silencer with Mean Flow and Nonlinear Incident Wave

Changjeon Hwang,Duck Joo Lee,Kang Seog Chae 대한기계학회 2007 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.21 No.1

Transmission losses of various reactive silencers are predicted, using a time accurate finite difference method. The numerical scheme is the 3rd order upwind scheme for axisymmetric Euler equations. Main advantage of the present method is that it can simulate linear and nonlinear wave propagation phenomena in a flow field directly with minimum numerical oscillation errors. The special treatments of incident wave condition, i.e. multiple harmonics of the transparent acoustic condition are applied to the transmission loss prediction for calculation efficiency. For the validation of the present approach, circular expansion chamber silencers without mean flow and an exponential pipe with mean flow are simulated in case of linear incident wave. The computed transmission losses have quite good agreements with those of the others. The nonlinear incident wave case is also investigated to check the usefulness of this method. The periodic N wave is clearly captured without numerical oscillation errors, and the insertion losses of two different incident frequencies are compared.

Conceptual Design of a Ducted Fan for Helicopter Anti-Torque System

Changjeon Hwang 한국항공우주학회 2005 International Journal of Aeronautical and Space Sc Vol.6 No.1

Ducted fans have advantages in noise as well as operational safety aspects compared to conventional tail rotors and are used as an anti-torque system for various classes of helicopters. The final goal of this study is to develop a ducted fan anti-torque system which can replace conventional tail rotors of existing helicopters to achieve safety enhancement and low noise level. In this paper, a conceptual design process and the results are described. Initially, the design requirement and the design parameter characteristics are analysed, and then initial sizing and configuration design are performed. There are several configuration changes due to specific technical reasons in each case. Finally, the required power and the pitch link load are predicted as an initial estimation. The conceptual design technique for the ducted fan in this study can be easily applied to the design of other ducted fans such as the lift fan for unmanned aerial vehicle.

Parametric Study for the Low BVI Noise Rotor Blade Design

Changjeon Hwang,Gene Joo 한국항공우주학회 2003 International Journal of Aeronautical and Space Sc Vol.4 No.1

민수헬기 시장분석

황창전(Hwang Changjeon),이정훈(Lee Junghoon),장병희(Chang Byunghee),황인희(Hwang Inhee) 한국항공우주연구원 2010 항공우주산업기술동향 Vol.8 No.1

본 논문에서는 우리산업이 민수시장진입을 위해서 필수적으로 분석해야 할 세계 민수시장의 범위 및 특성, 과거 실적치 등을 바탕으로 세계시장 및 국내시장 분석, 우리나라가 시장진입을 위해서 고려해야 할 사항 및 시장 전망에 대해서 다루었다. 분석을 통해 민수시장에서 대형단발급의 퇴조에 따라 쌍발시장이 커지며, 운용자 인터뷰를 통해 현재 운용 중인 헬기보다 상위급의 헬기 운용을 선호하게 되며, 전체 시장 규모 등 주도가치 측면 및 구현용이성으로 판단시 우리나라는 대형쌍발급 및 중소형쌍발급에서 전략적 포지셔닝을 갖는 것이 좋으며, 수리온 민수전환형은 상당량의 시장진입이 전망되나, 단가, 사양, 판매전략등 측면에서 적극적인 시장진입 노력이 필요하다. This paper deals with the world civil helicopter market scope, world market analysis based on the operating fleet ages, preconditions for market entry, and market forecast which are necessary for Korean industry to enter into world market. According to the analysis, the heavy single class demand is rapidly declined. The demand is moving toward the heavier class than that operated now. Korean industry had better have strategic positioning to heavy twin and light medium twin classes. A considerable amount of Korean civil helicopter based on Surion can be sold if there are appropriate efforts for price, specification, marketing strategy and so on.

전진비행하는 회전익기 로터의 평균 유입류 예측기법 연구

황창전(Changjeon Hwang),정기훈(Kihoon Chung) 한국항공우주학회 2007 韓國航空宇宙學會誌 Vol.35 No.2

동 연구에서는 전진비행하는 로터의 평균 유입류 예측기법 중 Drees 선형모델, 몇가지 변형된 형태의 Mangler & Squire 모델을 서로 비교하여 각 유입류 모델의 특성을 알아내고, KARI 자체 자유후류기법 코드의 해석결과를 함께 비교하여 각 유입류 예측기법의 특성을 파악하였다. 각 예측기법의 비교를 위해 유입류 실험치가 존재하는 로터에 대하여 전진비 0.15, 0.23 및 0.30의 3가지 비행조건을 적용하여 예측한 결과를 비교 분석하였다. Drees 모델의 경우 비교적 실험치에 근접하게 예측하나, 선형모델의 한계로 인해 유입류의 비균일성을 모델링하기에는 미흡하며, Mangler & Squire 모델은 끝단을 제외하고는 비교적 실험치에 근접하게 예측함을 알 수 있었으며, KARI의 자유후류기법은 유입류의 비균일성을 매우 잘 예측하나, 동체에 의한 올려흐름 효과, 후퇴부에서의 동적실속 효과 등의 추가 고려가 필요함을 알 수 있었다. Prediction methods for a rotor averaged inflow in forward flight are investigated in this study. The investigated methods are Drees linear inflow model, Mangler & Squire model and free vortex wake(FVW) method. Predictions have been performed for a four-blade rotor operating at three different advance ratios i.e. 0.15, 0.23 and 0.30, at which experimental data are available. According to results, Drees model has a limitation for the inflow non-uniformity prediction due to an inherent linear characteristics. Mangler & Squire model has a reasonable accuracy except the disk edge region. KARI FVW method has very good accuracy and has better accuracy than the other FVW method especially in inboard region. However, there are some discrepancies in retreating side due to the dynamic stall effect and in near hub region due to the fuselage upwash effect.

KARI의 헬리콥터 로터 소음관련 기술개발 현황

황창전(Changjeon Hwang),정기훈(Kihoon Chung),송근웅(Keunwoong Song),주진(Gene Joo),이욱(Wook Lee) 한국소음진동공학회 2006 한국소음진동공학회 학술대회논문집 Vol.2006 No.5

유ㆍ무인 회전익기 주요 설계변수의 추세선 식 유도 및 비교 분석 연구

황창전(Changjeon Hwang),김승범(Seungbum Kim) 한국항공우주학회 2006 韓國航空宇宙學會誌 Vol.34 No.2

동 연구에서는 유ㆍ무인 회전익기의 초기 사이징에 활용할 각종 설계변수에 대한 데이터베이스를 구축하여 추세선 식을 유도하고, 유ㆍ무인 회전익기 간 주요 설계변수의 특정을 비교 분석하여 회전익기 초기사이징의 용이성을 제고하고자 하였다. 연구접근방법으로 먼저 Jane 연감을 이용하여 유인기 78개 기종, 무인기 33개 기종에 대하여 데이터베이스를 구축하고, 구축된 데이터를 이용하여 회귀 분석을 통하여 총 6종의 추세선 식을 유도하였다. 계산된 상관계수와 결정계수에 따라 대부분의 추세선은 상대적으로 유의성이 있음을 알 수 있었다. 그리고, 유인 회전익기의 추세선 및 데이터베이스 그래프와 무인 회전익기 그래프 비교를 통하여 각 회전익기 간 주요 설계변수별 정성적 특정을 비교 분석하였다. 이를 통해 도출한 무인 회전익기의 몇가지 특정은 유인기에 비해 주로터 직경과 최대이륙중량은 작게, 꼬리로터 직경은 크게 설계하며, 자체무게비는 유인기와 유사한 수준이라는 것이다. Design parameters of manned and unmanned rotorcrafts have been investigated to construct a design database and to derive trend curves. Design parameters of 78 manned rotorcrafts and 33 unmanned rotorcrafts have been collected and analyzed using linear regression method. Six kinds of trend curves equations are derived. Most of trend curves derived are relatively meaningful according to the calculated correlation and determination coefficients. The comparisons between manned and unmanned rotorcraft characteristics are performed. It has been drawn according to the comparisons that unmanned rotorcraft has smaller main rotor diameter and maximum take-off weight, bigger tail rotor size and similar level of empty weight fraction than manned rotorcraft.

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.

국내 틸트로터 무인기 개발현황 및 실용화 계획

오수훈(Soohun Oh),황창전(Changjeon Hwang) 항공우주시스템공학회 2015 항공우주시스템공학회 학술대회 발표집 Vol.2015 No.11

eVTOL 탐색개발시제기 시험평가계획 수립

최주원(Joowon Choi),황창전(Changjeon Hwang),석진영(Jinyoung Suk) 한국항공우주학회 2023 한국항공우주학회 학술발표회 논문집 Vol.2023 No.4