The Numerical Simulation And Flow Control Of Micro Rotary-wings Flow Field Under Disturbance Wind

The flights of the micro air vehicles (MAVs) under low Reynolds number aresusceptible to the influence of extreme conditions such as gusts or sudden winds.Because of the mutation of their aerodynamic characters the emergence of severe joltor even overturn occurs. How to improve the steady-flight ability of MAV underperturbation wind environment, is still the main technical challenge for today’s MAVpractical process. In this thesis, the method of numerical simulation was used withflow control method, to study the flow filed of micro helicopter rotor underperturbation wind and periodic pitching motion control laws for rotor blades toeliminate the wind disturbances.The main works of the research are as follows:1. Because of the complex motion the rotor blades rotating and pitching, amulti-layer sliding grids technology was studied and developed. The ArbitraryLagrangian-Eulerian (ALE) formulations of Navier-Stokes equations are adopted asthe governing equations, then the multi-tier grid are adopted to implement thecomplex motion. The first grid layer is fixedly connected with the blade for pitchingmovement. The second grid layer is used to simulate the rotation of the rotor. Thethird layer is a stationary far flied grid. The outer boundary of each mesh layer canslide with the inner boundary of the outer mesh layer. Compared with the movingoverlapped grids technology, the multi-layer sliding grids technology also can depictthe local flow field and describe the relative motion between different components,without the complex grid processing process.2. A method to simulate the perturbation wind using grid velocity method wasstudied and developed. The idea is based on the principle of relative motion, themesh velocity is equal and opposite in direction with the disturbance wind speed.Based on the size of micro-rotor and the distribution of perturbation wind, the wind disturbance in the computational domain is synchronization at the same moment,namely wind disturbance is just a function of time, and nothing to do with space.Based on this assumption, the adoption of grid velocity method to describe theperturbation of wind makes the simulation simple and easy to operate. Theeffectiveness of this method also have been proved by the numerical results.3. The aerodynamic performance and flow control problems of micro singlerotors and miniature twin coaxial rotors under sinusoidal perturbation windenvironment are studied using the numerical techniques which are mentioned above.The results show that:(a) The curves of thrust for both two rotors are subjected tothe periodic perturbation wind action, and both response similar cyclical fluctuations.The fluctuation frequency and amplitude are proportional to the perturbationamplitude.(b) The use of periodic isometric pitching flow control method is able tofind suitable control parameters that can make rotor thrust fluctuations amplitudes besuppressed effectively under periodic perturbation wind environments.