Unsteady Aerodynamics Investigation For The Isolated Rotor In Large Amplitude Maneuvering Flight

The high-precision task capacity of a modern attack helicopter is ever-increasingly recognized and admired, which is testified by the fact that our nation develops the corresponding quality requirement about the flight maneuverability as a formal rating base. To ensure the safety and eligibility of maneuvers such as flips and rolling, this capability should be pre-proved and simulated in the design phase. So a comprehensive helicopter aerodynamics and flight dynamics model with considerable fidelity must be developed, and the prerequisite is to correctly describe the rotor unsteady aerodynamics.Combining theoretical analysis and experiment research, this dissertation investigated the unsteady aerodynamics of rotors in large-amplitude maneuvers, focusing the airfoil unsteady aerodynamic loading model, the rotor disk induced inflow model, the blade flapping model and their coupling. Consequently, aimed at the design and computation approaches of maneuver tasks, this work would serve as an academic base of flight dynamics researches for maneuvering helicopters, and provide the theoretical background for potential utilization of our prospective attack helicopters.The principal academic work involved in this dissertation was:1. Augmenting the Pitt-Peters inflow model and Peters-He finite states wake model to account for the wake distortion effect on disk inflow, and developing a flapping dynamics model applicable to a model maneuvering rotor;2. Modeling the airfoil unsteady aerodynamics including the effects of blade dynamic stall and air compressibility, and incorporating the wake distortion effect on induced velocity which is dependent upon the operating states;3. Developing a dynamic wake distortion model, and probing into the necessity and rationality of including rotor wake contraction effect and the gyroscopic feathering moment effect.In addition, the major experimental work was as follows:1. Testing by the whirling-beam test apparatus the large-amplitude pitching motions of model rotor with a smoking system, observing the geometrical changes of the tinged wake boundary, and constructing a wake distortion model determined by flight conditions; 2. Experimenting on rotor aerodynamics of undergoing large-amplitude pitching motions, obtaining the first-hand data of rotor loading response to quasi-step control inputs so as to serve as a reference data to validate and improve the current unsteady aerodynamic model.As for the simulation, the entire computation code, based upon the present rotor unsteady aerodynamic model, was compiled via MATLAB/SIMULINK. Furthermore, this program, applicable to calculating the unsteady aerodynamic responses of maneuvering rotors, can perform rotor trimming, model linearization and response prediction. Besides, much importance was attached to trimming solution and solver investigation of ordinary differential equationsAfter comparing the theoretical results with flight data, the most significant conclusions were in what follows:1. The two augmented inflow models, if combining quasi-steady wake distortion model, gained a distinct rotor off-axis response prediction from those without wake distortion effect, assuming a 180°phase discrepancy. Moreover, the results of Peters-He 15 state inflow model offered better correlation with the flight data. However, the wake distortion effect was negligible on the on-axis response;2. The wake curvature parameter was dependent upon maneuver angular rate, disk loading and forward speed. And the wake distortion was rather serious in hovers, and diminished with the translational speed. Accordingly a fixed parameter was inadequate to embody the aerodynamic environment of maneuvering rotors;3. When imposed was a step input of pitching or rolling angular rate, climbing rate or advance ratio upon an isolated rotor, the disk inflow alteration took on first-order characteristics with time. And the effects of wake curvature, skew and spacing could be incorporated into a dynamic wake distortion model by a set of ordinary differential equations;4. The augmented Peters-He 15 inflow model, combing with a time-accurate wake curvature parameter and the dynamic wake distortion model, could properly reflected the rotor off-axis response in agreement with the test products, but some discrepancy existed in amplitude. However, this situation would be ameliorated finitely when including gyroscopic feathering moment effect. Besides, the rotor wake contraction effect could be phased out from the comprehensive model.