Abstract
In the paper, a novel flapping mode is presented that can generate high lift force by a dragonfly wing in hover. The new mode, named partial advanced mode (PAM), starts pitching earlier than symmetric rotation during the downstroke cycle of the hovering motion. As a result, high lift force can be generated due to rapid pitching coupling with high flapping velocity in the stroke plane. Aerodynamic performance of the new mode is investigated thoroughly using numerical simulation. The results obtained show that the period-averaged lift coefficient, CL, increases up to 16% compared with that of the traditional symmetrical mode when an earlier pitching time is set to 8% of the flapping period. The reason for the high lift force generation mechanism is explained in detail using not only force investigation, but also by analyzing vortices produced around the wing. The proposed PAM is believed to lengthen the dynamic stall mechanism and enhance the LEV generated during the downstroke. The improvement of lift force could be considered as a result of a combination of the dynamic stall mechanism and rapid pitch mechanism. Finally, the energy expenditure of the new mode is also analyzed.
Highlights
In the last two decades, attention has increasingly been paid to the aerodynamic performance of insect wings [1,2,3,4,5] due to the rising popularity of micro air vehicles (MAVs) [6,7]
The results show that lift forces, the peak value and the period-averaged values, are dramatically improved by using partial advanced mode (PAM)
Peak lift force increases by 1.36 times, while period-averaged Cl increases by 16% in the 8%T PAM case, compared with those of the symmetrical rotation mode (SRM)
Summary
In the last two decades, attention has increasingly been paid to the aerodynamic performance of insect wings [1,2,3,4,5] due to the rising popularity of micro air vehicles (MAVs) [6,7]. MAVs with the capability of hovering flight, expensive form of flight [8] and exceptionally fine control is needed to remain stationary the of aerodynamic lift force generation of hovering is important to consider and Themechanism power produced by the flapping of insect wings should sustainflight the insect itself in the air. Compared to simple harmonic function, trapezoidal function exaggerates the acceleration at the the deceleration start at a later near timethe This pattern wing translation, combined with beginning and the deceleration end of). Inspired by Dickinson’s work [2], investigation of the high lift force generation of dragonfly wings by changing rotation timing are carried out in this study. The structure of this paper is as follows: the governing equations of the unsteady incompressible
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