Research On Rotor Dynamic Wake Modeling Based On Elliptical Vortex Ring Element

Handling quality has become one of the main design indicators of helicopters.Accurate and efficient helicopter flight dynamics model is the premise and key to the design and evaluation of handling quality.The rotor wake model is the core factor of flight dynamics modeling,which directly affects the model's accuracy and computational efficiency.This thesis studies a dynamic wake model suitable for steady and maneuvering flight,which can provide a new choice for improving the accuracy and computational efficiency of flight dynamics model.It has important application value for handling quality analysis and flight simulation.Firstly,the background and significance of the research are introduced.The developing process of the rotor wake model is reviewed.Several problems in the existing research are clarified,and the importance and necessity of the work in this thesis are set forth.Secondly,elliptical vortex ring elements with 8 degrees of freedom are presented to describe the rotor wake,and the generation model and equations of motion of the elliptical vortex ring elements are established.The velocity identification method of the vortex ring element is derived based on the least square method.Based on these elements,a new rotor dynamic wake model are constructed.The model is validated by the comparison with dynamic inflow model,circular vortex ring wake model and wind tunnel test data.Thirdly,in order to reduce the state order of the wake model,a model states reduction method based on the finite element concept is proposed,and then the reduced model is compared with the original model.Finally,the new wake model is coupled with the existing flight dynamics model.The trim and dynamic response characteristics of UH-60 helicopter are calculated,and the results are compared with those of the existing wake model and flight test data.The results show that the model can capture the main wake distortion effect,and the accuracy is relatively high not only in the trimmed flight but also in maneuvering flight.The state reduced wake model has the same accuracy with the original elliptical vortex ring wake model.