Mechanism analysis of the vortex ring and its effects on an axial descending rotor  

作　　者：Lifang Zeng Zeming Gao Tianyu Xu Liangquan Wang 

机构地区：[1]Zhejiang University,Hangzhou,Zhejiang 310027,China [2]Maritime New Zealand,Wellington 6011,New Zealand [3]New Zealand Migration Agency,Wellington 6037,New Zealand [4]China Aerodynamics Research and Development Center,Mianyang,Sichuan 621000,China

出　　处：《International Journal of Fluid Engineering》2024年第2期25-32,共8页国际流体工程(英文)

基　　金：supported by the National Natural Science Foundation of China (Grant No. 12202384);the Rotor Aerodynamics Key Laboratory Foundation of the China Aerodynamics Research and Development Center (Grant No. RAL202302-2)

摘　　要：A vortex ring is a flow phenomenon involving a complex toroidal vortex system. When a rotor is in descending flight, it may enter the vortex ring state(VRS), which will affect the rotor's aerodynamic characteristics and even endanger it. In this paper, to clarify the aerodynamic mechanism by which the vortex ring exerts its effects on an axial descending rotor, an unsteady numerical simulation method for the rotor integrated with structured moving overset grids is proposed and validated using experimental data. This numerical simulation method is then applied to analyze the aerodynamic characteristics of the rotor in descending flight. The variations of the aerodynamic forces and the flow characteristics in the slipstream are analyzed to elucidate the physical mechanisms responsible for the relationships between the aerodynamic loads, flow field, and vortices when the rotor is in the VRS. The effects of the VRS cause a sharp drop in the average aerodynamic forces, which directly affects the safety and reliability of a rotor aircraft. In the slipstream of the descending rotor, a distinct vortex ring forms and moves upward as the velocity of descent increases. The most severe VRS occurs at a nondimensional velocity of descent of 1.13 when the center of the highly unsteady vortex ring is right at the blade tip, and this can be used as an indicator of the VRS. The physical mechanism by which the VRS exerts its effects can be attributed to the low pressure induced by strong vortices. The VRS decreases the pressure on the lower surface of the blade and increases the pressure on the upper surface, resulting in a reduction in the aerodynamic loads. In comparison with the hovering state, the VRS results in a much larger vortex strength and possesses a different vortex structure.

关 键 词：VORTEX UNSTEADY BLADE 

分 类 号：V211.3[航空宇航科学与技术—航空宇航推进理论与工程]