Parametric Study of Two Rotor Cycloidal Blade System Using CFD Analysis for Cyclocopter Forward Flight

cycloidal blade system;cycloidal pitch motion;cyclocopter forward flight;CFD analysis;621

공과대학 기계항공공학부 ;

University:서울대학교 대학원

关键词: cycloidal blade system;    cycloidal pitch motion;    cyclocopter forward flight;    CFD analysis;    621;   

Others  :  http://s-space.snu.ac.kr/bitstream/10371/123685/1/000000009513.pdf

美国|英语

来源: Seoul National University Open Repository

【 摘 要 】

The cyclocopter is an aircraft that is capable of vertical take-off and landing using a cycloidal blade system. The cycloidal blade system consists of variable pitch blades that rotate around an axis which lies parallel to the spanwise direction of the blades. The model cyclocopter developed by Seoul National University has four rotors and maximum pitch angle and phase angle of the blades in each rotor are individually controlled. Each rotor has four blades and the controlled maximum pitch and phase angles are related to the magnitude and the direction of thrust force, respectively.In the modeled cyclocopter, two rotors are placed next to each other as a tandem type and the distance between the two is very close. Therefore, there is flow interference between the rotor during the hovering or the forward flight. It is necessary to understand the flow structure between those rotors to establish a control algorithm, which includes determining proper maximum pitch angle and phase angle for each flight situation. In this paper, CFD analysis is used for parametric study of two rotor cycloidal system. It was conducted with a transient method because the blades change its pitch angle periodically during a rotation. A two-dimensional finite volume mesh system contains front and rear rotors which is half of the modeled cyclocopter. Note here that only two rotors are needed for the two-dimensional CFD study since the other two rotors are aligned repetitively.Commercial softwares, ANSYS Fluent and ANSYS CFD-Post, were used for flow solving and post processing. To change pitch angle of the blades during a rotation that has a sinusoidal profile, a user defined function (UDF) was integrated into the Fluent as well as a sliding-mesh method. Each blade and each rotor are meshed with circular rotating zone that has a sliding interface with larger surrounding mesh system.Result from the two rotor system is different from a single rotor system in terms of force magnitude, efficiency of the system, and flow structure such as induced flow direction. In the forward flight case, rear rotor feels quite different incoming flow than the front rotor. This behavior can cause a failure due to imbalanced force of rotors. The degree of imbalance varies with velocity, posture, and flying direction. In order to overcome the imbalanced force of rotors, the flight posture should be tilted to forward to release the rear rotor from the downwash effect. In addition to this, the different pitch and phase conditions must be applied on those two rotors to maintain a stable flight. The major purpose of current analysis is to study the flows of the two-rotor cycloidal system and to obtain the dynamic characteristics of the rotors on various conditions in which velocity, pitch angle, phase angle, and posture are different. Hence, it is important to understand flow structures to predict flight stability and to build up control algorithm. The case studies will be followed to attain the most effective and efficient pitch angles and phase degrees for given velocity and posture conditions.