• Title, Summary, Keyword: aerodynamic stability

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NUMERICAL ANALYSIS FOR TURBULENT FLOW OVER A THREE DIMENSIONAL CAVITY WITH LARGE ASPECT RATION (세장비 변화에 따른 3차원 공동 주위의 난류유동 및 음향 특성에 관한 수치적 연구)

  • Mun, P.U.;Kim, J.S.
    • 한국전산유체공학회:학술대회논문집
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    • pp.13-18
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    • 2009
  • Flight vehicles such as wheel wells and bomb bays have many cavities. The flow around a cavity is characterized as an unsteady flow because of the formation and dissipation of vortices brought about by the interaction between the free stream shear layer and the internal flow of the cavity. The resonance phenomena can damage the structures around the cavity and negatively affect the aerodynamic performance and stability of the vehicle. In this study, a numerical analysis was performed for the cavity flows using the unsteady compressible three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equation with Wilcox's turbulence model. The Message Passing Interface (MPI) parallelized code was used for the calculations by PC-cluster. The cavity has aspect ratios (L/D) of 2.5 ~ 7.5 with width ratios (W/D) of 2 ~ 4. The Mach and Reynolds numbers are 0.4 ~ 0.6 and $1.6{\times}106$, respectively. The occurrence of oscillation is observed in the "shear layer and transient mode" with a feedback mechanism. Based on the Sound Pressure Level (SPL) analysis of the pressure variation at the cavity trailing edge, the dominant frequencies are analyzed and compared with the results of Rossiter's formula. The dominant frequencies are very similar to the result of Rossiter's formula and other experimental data in the low aspect ratio cavity (L/D = ~ 4.5). In the large aspect ratio cavity, however, there are other low dominant frequencies due to the leading edge shear layer with the dominant frequencies of the feedback mechanism. The characteristics of the acoustic wave propagation are analyzed using the Correlation of Pressure Distribution (CPD).

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The Study of Advanced Propeller Blade for Next Generation Turboprop Aircraft -Part II. Static Structural Design and Test (차세대 터보프롭 항공기용 최신 프로펠러 블레이드 연구 -Part II. 정적 구조 설계 및 시험)

  • Choi, Won;Park, Hyun-Bum;Kong, Chang-Duk
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.42 no.4
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    • pp.336-343
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    • 2014
  • Modern advanced-turboprop propellers are required to have high structural strength to cope with the thrust requirement at high speed. The high stiffness and strength carbon/epoxy composite material is used for the major structure and skin-spar-foam sandwich structural type is adopted for advantage in terms of the blade weight. As a design procedure for the present study, the structural design load is estimated through investigation on aerodynamic load and then flanges of spars from major bending loads and the skin from shear loads are sized using the netting rule and Rule of Mixture. In order to investigate the structural safety and stability, stress analysis is performed by finite element analysis code MSC. NASTRAN. It is found that current methodology of composite structure design is a valid method through the static structural test of prototype blade.

A Study on Optimmal Design of Filament Winding Composite Tower for 2 MW Class Horizontal Axis Wind Turbine Systems (2 MW급 대형 수평축 풍력발전시스템을 위한 필라멘트 와인딩 복합재 타워의 최적설계에 관한 연구)

  • Lim, Sung-Jin;Kong, Chang-Duk;Park, Hyun-Bum
    • Composites Research
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    • v.25 no.2
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    • pp.54-61
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    • 2012
  • In this study, a specific structural design procedure for 2 MW class glass/epoxy composite wind turbine system towers is newly proposed through load case study, trade-off study, optimal structural design and structural analysis. Optimal tower design is very important because its cost is about 20% of the wind turbine system's cost. In the structural design of the tower, three kinds of loads such as wind load, blades, nacelle and tower weight and blade aerodynamic drag load should be considered. Initial structural design is carried out using the netting rule and the rule of mixture. Then the structural safety and stability are confirmed using a commercial finite element code, MSC NASTRAN/PATRAN. The finally proposed tower configuration meets the tower design requirements.

Experimental Study on the Aerodynamic Characteristics of the Ducted fan for the Propulsion of a Small UAV (소형 무인항공기 추진용 덕티드팬의 공력특성에 대한 실험적 연구)

  • Ryu, Min-Hyoung;Cho, Lee-Sang;Cho, Jin-Soo
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.40 no.5
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    • pp.413-422
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    • 2012
  • The ducted fan for a small UAV propulsion can reconnoiter and observe in a town and a small area, it has better thrust efficiency and a long endurance than propeller. Thrust characteristics of hover and for ward flight condition for the ducted fan UAV is important issue to improve a endurance. The unsteady 3-dimensional flow fields of the ducted fan UAV is essential to stable flight. In this paper, to verify the design results of the ducted fan and to investigate a stable aeronautical characteristic, the thrust performance and the unsteady 3-dimensional flow fields are measured. Thrust characteristics for the hovering and the forward flight conditions are measured by the 6-components balance system in the subsonic wind tunnel. The unsteady 3-dimensional flow fields are analyzed by using a stationary $45^{\circ}$ slanted hot-wire technique. The swirl velocity is almost removed behind the stator blades. Therefore, the thrust performance of the ducted fan is improved and the flight stability is maintained.

Developing High Altitude Long Endurance (HALE) Solar-powered Unmanned Aerial Vehicle (UAV) (고고도 장기체공 태양광 무인기 개발)

  • Hwang, SeungJae;Kim, SangGon;Lee, YungGyo
    • Journal of Aerospace System Engineering
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    • v.10 no.1
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    • pp.59-65
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    • 2016
  • Korea Aerospace Research Institute (KARI) is developing an electric-driven HALE UAV in order to secure system and operational technologies since 2010. Based on the 5 years of flight tests and design experiences of the previously developed electric-driven UAVs, KARI has designed EAV-3, a solar-powered HALE UAV. EAV-3 weighs 53 kg, the structure weight is 21 kg, and features a flexible wing of 19.5 m in span with the aspect ratio of 17.4. Designing the main wing and empennage of the EAV-3 the amount of the bending due to the flexible wing, 404 mm at 1-G flight condition based on T-800 composite material, and side wind effects due to low cruise speed, V_cr = 6 m/sec, are carefully considered. Also, unlike the general aircraft there is no center of gravity shift during the flight. Thus, the static margin cuts down to 28.4% and center of gravity moves back to 31% of the Mean Aerodynamic Chord (MAC) comparing to the previously developed scale-down HALE UAVs, EAV-2 and EAV-2H, to minimize a trim drag and enhance a performance of the EAV-3. The first flight of the EAV-3 has successfully conducted on the July 29, 2015 and the test flight above the altitude 14 km has efficiently achieved on the August 5, 2015 at the Goheung aviation center.

A Study on Experimental Test of a Small Scale Hingeless Rotor (축소형 무힌지 로터 시험에 관한 연구)

  • Kim, Joune-Ho;Song, Keun-Woong;Joo, Gene;Suk, Jin-Young
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.35 no.12
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    • pp.1599-1606
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    • 2011
  • It is possible to study the load characteristics of full-scale hingeless rotor with the changing of physical smallscaled configurations such as rectangular and paddle blades, and metal and composite hubs. In this study, a static test, and a ground and wind-tunnel test were carried out using small-scale rotor models. The static test was carried out to confirm structural stiffness, characteristics of inertia, natural frequency, and damping ratio of rotors, and the ground and wind-tunnel test was carried out to confirm the stability and aerodynamic characteristics under hovering and forward flight conditions. According to the test results, the vertical load in the case of a combination of a small composite hub with paddle blades was higher than that in the case of a metal hub with paddle blades at same condition. Further, it was confirmed that the restraint of the combination of composite hub can be more flexible than the metal hub for the motion of paddle blades.

Structural Analysis of Floating Offshore Wind Turbine Tower Based on Flexible Multibody Dynamics (탄성 다물체계 동역학을 기반으로 한 부유식 해상 풍력 발전기 타워의 구조 해석)

  • Park, Kwang-Phil;Cha, Ju-Hwan;Ku, Namkug;Jo, A-Ra;Lee, Kyu-Yeul
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.36 no.12
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    • pp.1489-1495
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    • 2012
  • In this study, we perform the structural analysis of a floating offshore wind turbine tower by considering the dynamic response of the floating platform. A multibody system consisting of three blades, a hub, a nacelle, the platform, and the tower is used to model the floating wind turbine. The blades and the tower are modeled as flexible bodies using three-dimensional beam elements. The aerodynamic force on the blades is calculated by the Blade Element Momentum (BEM) theory with hub rotation. The hydrostatic, hydrodynamic, and mooring forces are considered for the platform. The structural dynamic responses of the tower are simulated by numerically solving the equations of motion. From the simulation results, the time history of the internal forces at the nodes, such as the bending moment and stress, are obtained. In conclusion, the internal forces are compared with those obtained from static analysis to assess the effects of wave loads on the structural stability of the tower.

Capsule Train Dynamic Model Development and Driving Characteristic Analysis Considering the Superconductor Electrodynamic Suspension (초전도 유도 반발식 부상특성을 고려한 캡슐트레인 동특성 해석 모델 구축 및 주행 특성 분석)

  • Lee, Jin-Ho;Lim, Jungyoul;You, Won-Hee;Lee, Kwansup
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.21 no.7
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    • pp.38-45
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    • 2020
  • A magnetically levitating capsule train, which runs inside the sub-vacuum tube, can reach ultra-fast speeds by dramatically reducing the aerodynamic drag and friction. The capsule train uses the superconductor electrodynamic suspension (SC-EDS) method for levitation. The SC-EDS method has advantages, such as a large levitation gap and free of gap control, which could reduce the infra-construction cost. On the other hand, disadvantages, such as the large variation of the levitation-guidance gap and small damping characteristics in levitation-guidance force, could degrade the running stability and ride comfort of the capsule train. In this study, a dynamic analytical model of a capsule train based on the SC-EDS was developed to analyze the running dynamic characteristics. First, as important factors in the capsule train dynamics, the levitation and guidance stiffness in the SC-EDS system were derived, which depend non-linearly on the velocity and gap variation. A 3D dynamic analysis model for capsule trains was developed based on the derived stiffness. Through the developed model, the effects of the different running speeds on the ride comfort were analyzed. The effects of a disturbance from infrastructure, such as the curve radius, tube sag, and connection joint difference, on the running stability of the capsule train, were also analyzed.

Parametric Study on Wing Design of Insect-mimicking Aerial Vehicle with Biplane Configuration (겹 날개를 사용하는 곤충 모방 비행체의 날개 형상에 대한 파라메트릭 연구)

  • Park, Heetae;Kim, Dongmin;Mo, Hyemin;Kim, Lamsu;Lee, Byoungju;Kim, Inrae;Kim, Seungkeun;Ryi, Jaeha;Choi, Jong-Soo
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.46 no.9
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    • pp.712-722
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    • 2018
  • This paper conducts parametric studies on flapping wing design, one of the most important design parameters of insect-mimicking aerial vehicles. Experimental study on wing shape was done through comparison and analysis of thrust, pitching moment, power consumption, and thrust-to-power ratio. A two-axis balance and hall sensor measure force and moment, and flapping frequency, respectively. Wing configuration is biplane configuration which can develop clap and fling effect. A reference wing shape is a simplified dragonfly's wing and studies on aspect ratio and wing area were implemented. As a result, thrust, pitching moment, and power consumption tend to increase as aspect ratio and area increase. Also, it is found that the flapping mechanism was not normally operated when the main wing has an aspect ratio or area more than each certain value. Finally, the wing shape is determined by comparing thrust-to-power ratio of all wings satisfying the required minimum thrust. However, the stability is not secured due to moment generated by disaccord between thrust line and center of gravity. To cope with this, aerodynamic dampers are used at the top and bottom of the fuselage; then, indoor flight test was attempted for indirect performance verification of the parametric study of the main wing.