Abstract
The rotorcraft blade tip vortex rolled up by the blade tip when the rotor rotates at high speed will produce a complex induced velocity field, which will have an important impact on the aerodynamic load and performance of the rotor. For this reason, this paper carries out the research on the identification of blade tip vortex and the motion characteristics of the vortex. Through the time-resolved particle image velocimetry (TR-PIV) experiment, the flow field of the rotor at a fixed rotate speed (2100 r/min) with a collective pitch of 6° and 9° was obtained. Based on the vorticity field, Q criterion, and Ω criterion, the research on vortex identification and vortex motion characteristics are realized. The results show that with the increase of blade motion azimuth, the radial position of blade tip vortex gradually contracts inward and the axial position moves downward in hovering state. As the collective pitch of the rotor increases, the radial contraction becomes more obvious, and the axial displacement increases, at the same time, the blade tip vortex intensity increases. Comparative study results show that different vortex identification methods have obtained certain deviations in the vortex center. Compared with other vortex identification methods, the Ω criterion method has a smaller deviation and can accurately identify the vortex core radius and vortex boundary.
Highlights
The flow field structure around the rotor is more complicated than the fixed-wing, and its aerodynamic complexity is partly due to the unique aerodynamic environment around the rotor [1,2,3,4].The rotor is subject to additional non-inertial forces due to rotation, such as Coriolis and centrifugal forces, the non-linear phenomena in the vortex evolution are more obvious, and the flow characteristics are more abundant
These vortices are always close to the rotor, generating a complex three-dimensional induced flow field, which affects the aerodynamic load of the rotor, aerodynamic performance, vibration level, aeroelasticity and acoustic performance [1,5,6,7]
Through the Particle image image velocimetry velocimetry (PIV) test, the flow field induced by rotor blade tip vortex under different experimental conditions were obtained
Summary
The flow field structure around the rotor is more complicated than the fixed-wing, and its aerodynamic complexity is partly due to the unique aerodynamic environment around the rotor [1,2,3,4]. The Ω vortex identification method proposed by Liu solved uncertainty brought by the choice of the threshold value This vortex identification method was applied to the research of the rotor wake flow field, how to accurately define and identify the vortex structures and further analyze the interaction mechanism between vortex systems needs further verification and engineering. For this purpose, this paper uses the time-resolved particle image velocimetry (TR-PIV) technology as a research tool for rotor flow field measurement and performs precise measurement experiments on the rotor blade tip vortex in hovering state. The research methods and results of this paper can be used to analyze the generation, evolution, and interaction mechanism of vortices in rotor wakes, and provide a theoretical basis for wake vortex modeling and control
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