Summary of low-speed longitudinal aerodynamics of two powered close-coupled wing-canard fighter configurations

Investigations of the low speed longitudinal characteristics of two powered close coupled wing-canard fighter configurations are discussed. Data obtained at angles of attack from -2 deg to 42 deg, Mach numbers from 0.12 to 0.20, nozzle and flap deflections from 0 deg to 40 deg, and thrust coefficients from 0 to 2.0, to represent both high angle of attack subsonic maneuvering characteristics and conventional takeoff and landing characteristics are examined. Data obtained with the nozzles deflected either 60 deg or 90 deg and the flaps deflected 60 deg to represent vertical or short takeoff and landing characteristics are discussed

Effect of Rotor Blade Geometry on the Performance of Rotary-Winged Micro Air Vehicle

The development of physics based analysis to predict the hover performance of a micro rotor system meant for a hover capable micro air vehicle for studying the role of blade geometric parameters (such as planform, twist etc.) is discussed. The analysis is developed using blade element theory using lookup table for the sectional airfoil properties taken from literature. The rotor induced inflow is obtained using blade element momentum theory. The use of taper seems beneficial in improving the hover efficiency for lower values of thrust coefficient. For rotors operating at high thrust conditions, high negative twist is desirable. There is no unique blade geometry which performs well under all thrust conditions. This well validated analysis can be used for design of hover capable micro air vehicles

Research requirements for development of improved helicopter rotor efficiency

The research requirements for developing an improved-efficiency rotor for a civil helicopter are documented. The various design parameters affecting the hover and cruise efficiency of a rotor are surveyed, and the parameters capable of producing the greatest potential improvement are identified. Research and development programs to achieve these improvements are defined, and estimated costs and schedules are presented. Interaction of the improved efficiency rotor with other technological goals for an advanced civil helicopter is noted, including its impact on engine noise, hover and cruise performance, one-engine-inoperative hover capability, and maintenance and reliability

modeling and optimization

학위논문(박사)--서울대학교 대학원 :공과대학 기계항공공학부(멀티스케일 기계설계전공),2020. 2. 최해천.The aerodynamic characteristics of a hovering rhinoceros beetle are numerically and theoretically investigated. Its wing kinematics is measured using high speed cameras and used for numerical simulation of flow around a flapping rhinoceros beetle in hovering flight. The numerical results show that the aerodynamic forces generated (especially for lift) and power required by the hind wing during a quasi-periodic state are quite different from those during the first stroke. This indicates that the wing-wake interaction significantly affects the aerodynamic performance of the hind wing during the quasi-periodic state. Also, twisting of the hind wing along the wing span direction does not much contribute to total force generation as compared to that of the flat wing, and the role of elytron and body on the aerodynamic performance is quite small at least for the present hovering flight. Based on a previous model (Wang et al., J. Fluid Mech., vol. 800, 2016, pp. 688-719), we suggest an improved predictive aerodynamic model without any ad hoc model constants for a rigid and flat hind wing by considering the effect of the wing-wake interaction in hovering flight. In this model, we treat the wake as a steady or unsteady non-uniform downwash motion and obtain its magnitude by combining a quasi-steady blade element theory with an inviscid momentum theory. The lift and drag forces and aerodynamic power consumption predicted by this model are in excellent agreements with those obtained from numerical simulations. Based on the developed quasi-steady aerodynamic model, the optimal planform shapes and motions of the hind wing of the hovering beetle for minimum power consumption are investigated. First, we optimize wing motions with the measured wing planform shape for minimum aerodynamic and positive mechanical power consumptions, respectively. We also optimize wing planform shapes with the measured wing motion, as done for the optimization of the wing motion. We find that the measured wing shape is not optimal in terms of aerodynamic power consumption and the optimal wing shape and motion minimizing positive mechanical power consumption are close to the measured ones. For minimum aerodynamic power consumption, the pitching axis of the wing should be located between the 1/4-chord and the mid-chord points, together with the radius of the first moment of wing area of around 0.5. For minimum positive mechanical power consumption, the wing area should be concentrated near the wing root rather than the aerodynamically optimal wing shape, and the pitching axis is between the leading edge and the 1/4-chord point.정지 비행하는 장수풍뎅이의 공기 역학적 특성을 수치적-이론적으로 조사하였다. 날갯짓은 고속 카메라를 통해 측정되었으며, 정지 비행하는 장수풍뎅이 주변의 유동을 수치해석하는 데 사용되었다. 수치해석 결과는 준주기적 상태일 때 속날개로부터 발생되는 힘(특히 양력)과 공기 역학적 요구전력이 첫 번째 날갯짓 동안의 힘 및 공기 역학적 요구전력과 상당히 다르다는 것을 보여준다. 이는 날개-후류 간 상호작용이 준주기적 상태동안 속날개의 공력 특성에 크게 영향을 미친다는 것을 나타낸다. 또한 속날개의 날개 길이 방향에 따른 비틀림은 편평한 속날개와 비교할 때 전체 힘 생성에 크게 기여하지 않으며 공기 역학적 성능에 대한 겉날개와 몸통의 역할은 적어도 현재의 정지 비행에 대해 매우 작음을 확인하였다. 기존의 공력 모델을 바탕으로 날개-후류 간 상호작용의 효과를 고려하여 정지 비행하는 편평한 속날개에 대해 어떠한 모델 상수도 없는 개선된 예측적 공력 모델을 제안하였다. 이 공력 모델에서 후류를 비균일의 정상 또는 비정상 하강기류로 간주하고, 준정상 블레이드 요소 이론과 비점성 운동량 이론을 결합하여 후류의 세기를 구하였다. 현재의 공력 모델로 예측된 양, 항력 및 공기 역학적 요구전력은 수치해석으로부터 얻어진 결과와 매우 잘 일치하였다. 개발된 준정상 공력 모델을 기반으로, 최소 전력 소비를 위한 정지 비행하는 장수풍뎅이 속날개의 최적 평면 형상 및 움직임을 조사하였다. 먼저, 최소 공기 역학적 및 양의 기계적 전력 소비를 위해 측정된 날개 평면 형상으로 날개 움직임을 최적화하였다. 또한 날개 움직임의 최적화를 위해 수행된 것 처럼 측정된 날개 움직임으로 날개 평면 형상을 최적화하였다. 최적화 결과로부터 측정된 날개 형상은 공기 역학적 요구전력 측면에서 최적이 아니며, 양의 기계적 전력 소비를 최소화하는 날개 모양과 움직임이 측정된 것들에 가깝다는 것을 확인하였다. 최소 공기 역학적 전력 소비를 위해서는 날개 면적의 첫 번째 모멘트의 반경은 약 0.5이며, 날개의 피칭 축이 시위 길이의 1/4 지점과 1/2 지점 사이에 있어야함을 확인하였다. 최소 양의 기계적 전력 소비를 위해서는 최소 공기 역학적 전력 소비를 위한 날개보다 날개 면적이 날개 뿌리 근처에 모여있어야하며, 피칭 축은 선단과 시위 길이의 1/4 지점 사이에 있어야함을 확인하였다.Part I A numerical and theoretical study of the aerodynamic performance of a hovering rhinoceros beetle (Trypoxylus dichotomus) 1 1 Introduction: Why rhinoceros beetle? 2 2 Wing kinematics and morphological parameters 7 2.1. Measurement of the wing kinematics 7 2.2. Measured wing kinematic and morphological parameters 8 3 Numerical details 17 4 Simulation results 23 5 Quasi-steady aerodynamic model of a flapping wing in hover 35 5.1. Quasi-steady blade element theory 36 5.2. Estimation of induced downwash motion 43 6 Model validation and discussions 50 7 Further consideration on the induced downwash motion 62 8 Conclusions 68 Part II Optimal wing geometry and kinematics of a hovering rhinoceros beetle for minimum power consumption 71 1 Introduction 72 2 Models for a hovering flight of a rhinoceros beetle 75 2.1. Wing motion and shape 76 2.2. Aerodynamic force and power expenditure 79 3 Optimization 84 4 Results and discussion 88 4.1. Optimal wing motions for the measured wing shape 88 4.2. Optimal wing shapes for the measured wing motion 90 4.3. Numerical simulation on the optimal wing motions and shapes 92 5 Conclusion 104 References 106 Appendix 114 A A predictive model of the drag coefficient for a revolving wing at low Reynolds number 114 A.1. Introduction 114 A.2. An improved model of the drag coefficient 117 A.3. Results and discussion 122 A.4. Conclusion 123 Abstract (in Korean) 128Docto

The development of CFD methods for rotor applications

The optimum design of the advancing helicopter rotor for high-speed forward flight always involves a tradeoff between transonic and stall limitations. However, the preoccupation of the rotor industry was primarily concerned with stall until well into the 1970s. This emphasis on stall resulted from the prevalent use of low-solidity rotors with rather outdated airfoil sections. The use of cambered airfoil sections and higher-solidity rotors substantially reduced stall and revealed the advancing transonic flow to be a more persistent limitation to high-speed rotor performance. Work in this area was spurred not only by operational necessity but also by the development of a tool for the prediction of these flows (the method of computational fluid dynamics). The development of computational fluid dynamics for these rotor problems was a major Army and NASA achievement. This work is now being extended to other rotor flow problems. The developments are outlined

High performance forward swept wing aircraft

A high performance aircraft capable of subsonic, transonic and supersonic speeds employs a forward swept wing planform and at least one first and second solution ejector located on the inboard section of the wing. A high degree of flow control on the inboard sections of the wing is achieved along with improved maneuverability and control of pitch, roll and yaw. Lift loss is delayed to higher angles of attack than in conventional aircraft. In one embodiment the ejectors may be advantageously positioned spanwise on the wing while the ductwork is kept to a minimum

Efficiency of Lift Production in Flapping and Gliding Flight of Swifts

Many flying animals use both flapping and gliding flight as part of their routine behaviour. These two kinematic patterns impose conflicting requirements on wing design for aerodynamic efficiency and, in the absence of extreme morphing, wings cannot be optimised for both flight modes. In gliding flight, the wing experiences uniform incident flow and the optimal shape is a high aspect ratio wing with an elliptical planform. In flapping flight, on the other hand, the wing tip travels faster than the root, creating a spanwise velocity gradient. To compensate, the optimal wing shape should taper towards the tip (reducing the local chord) and/or twist from root to tip (reducing local angle of attack). We hypothesised that, if a bird is limited in its ability to morph its wings and adapt its wing shape to suit both flight modes, then a preference towards flapping flight optimization will be expected since this is the most energetically demanding flight mode. We tested this by studying a well-known flap-gliding species, the common swift, by measuring the wakes generated by two birds, one in gliding and one in flapping flight in a wind tunnel. We calculated span efficiency, the efficiency of lift production, and found that the flapping swift had consistently higher span efficiency than the gliding swift. This supports our hypothesis and suggests that even though swifts have been shown previously to increase their lift-to-drag ratio substantially when gliding, the wing morphology is tuned to be more aerodynamically efficient in generating lift during flapping. Since body drag can be assumed to be similar for both flapping and gliding, it follows that the higher total drag in flapping flight compared with gliding flight is primarily a consequence of an increase in wing profile drag due to the flapping motion, exceeding the reduction in induced drag

Designing the Human-Powered Helicopter: A New Perspective

The concept of human-powered vertical flight was studied in great depth. Through the manipulation of preexisting theory and analytical methods, a collection of design tools was created to expediently conceptualize and then analyze virtually any rotor. The tools were then arranged as part of a complete helicopter rotor design process. The lessons learned as a result of studying this process—and the tools of which it consists—are presented in the following discussion. It is the belief of the author that by utilizing these tools, as well as the suggestions that accompany them, future engineers may someday build a human-powered helicopter capable of winning the Sikorsky Prize