| As an important feature of helicopter rotor flow field, the rotor wake has been a hot and difficult point for research in the area of Helicopter Aerodynamics. A new and high‐revolution rotor wake simulation method has been studied in this paper based upon the discrete viscosity‐vortex method as well as the fast multiple method. Then a highly efficient rotor wake analysis model is established by combining the above method with Weissinger‐L lifting surface theory, and a hybrid computational method is developed for rotor unsteady flow field by coupling CFD method. Using the developed method, the flow field and aerodynamic characteristics of helicopter rotors at different operating conditions are calculated and analyzed. Particularly, the more complicated tiltrotor flow characteristics are deeply researched based on the developed method and available experimental rig. The major contributions of the author’s research work are as follows:As the background of the work, the research purposes are firstly described, and the research status of the rotor flow‐field numerical methods at home and abroad are summarized which include the helicopter rotor free‐wake method, the rotor CFD method and the hybrid numerical method. The difficulties and the shortages in the current discrete methods/models are pointed out and the solutions in this paper are briefly introduced.According to the characteristics of the rotor flow field, a high‐revolution rotor wake analysis method is developed based upon the discrete viscosity‐vortex method. In this method, in order to improve the numerical stability and computational efficiency, on the one hand, the control method for nonuniform distribution of vortex particles which are suitable for rotor wake calculation, the adaptive vortex‐particles growth control mechanism and the vorticity divergence control strategy are applied to modify the discrete vortex particles. On the other hand, a multilevel adaptive fast multiple method is introduced into the calculation of induced velocity and its gradient to improve the computational efficiency.Based on the present viscous vortex method a new rotor wake model is developed by combining with the Weissinger‐L lifting surface model. For improving the computing capability of the present model in rotor aerodynamic characteristics, the Beddoes nonlinear airfoil stall model and Selig spanwise flow modified model are adopted in the loading calculation. At the same time, to combine rotor trim model, an highly efficient and general “delta method” trim strategy is developed. By the developed method, the numerical simulations are maded for Boatwright test rotor, Caradonna&Tung rotor, Elliott rotor as well as Helicopter H‐34one, the validity of the method is verified and its numerical characteristic is analyzed. Furthermore, aiming at the disadvantage of lifting surface model that may not capture the blade flow field in detail, a newly hybrid method is developed for rotor unsteady flow field by coupling the present with CFD method. Using this hybrid method, the numerical simulation is carried out for Caradonna&Tung rotor, Helishpae7A test rotor and UH‐60A helicopter one. The unique characteristics of the hybrid method is emphatically analyzed in computational precision and efficiency, meanwhile the validity of the method is verified.Finally, by the developed numerical method and the rotor‐rig experiments, the tiltrotor flow field which is more complicated is investigated, including:(1) the influence of blade highly‐twisted feature on the rotor wake and aerodynamics;(2) the rotor wake characteristics at the condition of dual tiltrotors intereraction;(3) the characteristics of the rotor/wing interaction flow field and its influence on the aerodynamics of both rotor and wing. On the basis of above research, some new conclusions are presented which are of practical significance for the tiltrotor design. |
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