Abstract
Aerodynamic performance and agility during flapping flight are determined by the combination of wing shape and kinematics. The degree of morphological and kinematic optimisation is unknown and depends upon a large parameter space. Aimed at providing an accurate and computationally inexpensive modelling tool for flapping-wing aerodynamics, we propose a novel CFD (computational fluid dynamics)-informed quasi-steady model (CIQSM), which assumes that the aerodynamic forces on a flapping wing can be decomposed into the quasi-steady forces and parameterised based on CFD results. Using least-squares fitting, we determine a set of proportional coefficients for the quasi-steady model relating wing kinematics to instantaneous aerodynamic force and torque; we calculate power with the product of quasi-steady torques and angular velocity. With the quasi-steady model fully and independently parameterised on the basis of high-fidelity CFD modelling, it is capable of predicting flapping-wing aerodynamic forces and power more accurately than the conventional blade element model (BEM) does. The improvement can be attributed to, for instance, taking into account the effects of the induced downwash and the wing tip vortex on the force generation and power consumption. Our model is validated by comparing the aerodynamics of a CFD model and the present quasi-steady model using the example case of a hovering hawkmoth. It demonstrates that the CIQSM outperforms the conventional BEM while remaining computationally cheap, and hence can be an effective tool for revealing the mechanisms of optimization and control of kinematics and morphology in flapping-wing flight for both bio-flyers and unmanned air systems.
Highlights
Insects take to the air and manoeuvre in three-dimensional space by generating finely tuned aerodynamic force with their flapping wings
Time courses of simulated aerodynamic forces and power generated by a single flapping wing with realistic wing kinematics are illustrated in figure 5
Further remarks and conclusion The demonstration with power minimization and the probability distributions of the errors and Pearson correlation coefficient (PCC) in figure 9 indicate that the CFD-informed quasisteady model (CIQSM) outperforms the conventional blade element model (BEM) in terms of its accuracy
Summary
Insects take to the air and manoeuvre in three-dimensional space by generating finely tuned aerodynamic force with their flapping wings. Kang & Shyy (2014) utilized a BEM for constructing a fluid–structure interaction model by combining it with a structural model. These attempts improved the reliability of the BEM and enabled application to various aerodynamic studies such as the dynamics and control of flapping fliers (Hedrick & Daniel 2006; Bergou, Xu & Wang 2007; Hedrick, Cheng & Deng 2009; Kim & Han 2014) and the optimization of wing kinematics (Berman & Wang 2007; Zheng, Hedrick & Mittal 2013)
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