Unsteady aerodynamic and optimal kinematic analysis of a micro flapping wing rotor

Abstract

Inspired by the high performance of rotary and insect flapping wings capable of vertical takeoff and landing and hovering (VTOLH), a novel flapping wing rotor (FWR) has been developed by combining the above two types of wing motions. The FWR offers an alternative configuration for micro air vehicles (MAV) of such high flight performance. Unlike the well-studied aerodynamics of rotary and insect-like flapping wing with prescribed wing motion, the aerodynamic lift and efficiency of the FWR associated with optimal kinematics of motion has not been studied in a systematic manner before. This investigation is therefore focused on the FWR optimal kinematic motion in terms of aerodynamic lift and efficiency. Aerodynamic analysis is conducted for a FWR model of aspect ratio 3.6 and wing span 200mm in a range of kinematic parameters. The analysis is based on a quasi-steady aerodynamic model with empirical coefficients and validated by CFD results at Re~3500. For comparison purpose, the analysis includes rotary and insect-like flapping wings in hovering status with the FWR at an equilibrium rotation speed when the thrust equals to drag. The results show that the rotary wing has the greatest power efficiency but the smallest lift coefficient. Whereas the FWR can produce the greatest aerodynamic lift with power efficiency between rotary and insect-like flapping wings. The results provide a quantified guidance for design option of the three types of high performance MAVs together with the optimal kinematics of motion according to flight performance requirement.

Analysis and experiment of a bio-inspired flyable micro flapping wing rotor

“…Unlike the aerodynamic force, the mean lift coefficient of the FWR does not vary progressively with the input power. Although the lowest input 2.5v resulted in the highest ̅ = 1.26 for the FWR model, the passive kinematics of motion ( u =38 o ,  d =7 o ) is not close to the optimal solution shown in previous study ( u =18 o ,  d =-3 o [21]). The results indicate that an optimal FWR kinematics of motion for maximum ̅ requires a prescribed actuation rather than achieved by passive twist.…”

“…In the down-stroke, the variation and magnitude of the aerodynamic force and (negative) pitching moment are significantly greater than the up-stroke. The pitching moment produced a large variation of (negative) aeroelastic twist angle from -8 o~-37 o that resulted in the  d varied from [21]. It is also interesting to note that the St of the FWR falls in the range of optimal propelling efficiency 0.25~0.4 as demonstrated by flying animals [28] over the input power range as shown in Table 2 and Fig.…”

“…The maximum difference of the QS model in lift and rotational moment coefficients are less than 12% and 15% respectively compared with 3D CFD results for a range of kinematic parameters. The details of the model validation and comparison are provided in the previous study [21].…”

“…In a recent work by the authors [21,22], the optimal kinematics of motion for FWR was identified and the aerodynamic lift and efficiency were calculated and compared with the conventional rotary and insect-like flapping wings. The results showed that the FWR can produce significantly greater aerodynamic lift coefficient and power efficiency than the insect-like flapping wings.…”

Unsteady aerodynamic model of flexible flapping wing

“…Wang et al [7] used numerical simulation to model the forces and flow of a flapping 2D aerofoil and showed that significant lift can be obtained for the wing within 2-4 chord lengths of travel by making use of the dynamic stall of the LEV. Li et al [8] have extended the study of aerodynamic lift and efficiency of insect flapping wing in comparison with rotary and a novel flapping wing rotor.…”