The coupling mechanism between the transient rotary speed and the flow field of the flapping-wing rotor via dynamic fluid–body interaction modeling

To help understand the flow field mechanisms behind the entire process of a flapping-wing rotor (FWR) from startup to dynamic equilibrium of rotary motion, this study develops a dynamic fluid–body interaction (DFBI) model to predict the aerodynamics of the FWR, wherein the DFBI model is used to accurately realize the wing's motions within the simulation. The computational fluid dynamics model in this work is rigorously validated through grid independence studies, time-step independence studies, model independence studies, and comparison with prior data. An experimental lift measurement platform is also constructed. Based on these tools, this study investigates the coupling mechanism between transient rotary speed and flow field and the effect of reduction ratio on the FWR's aerodynamic performance. Key findings indicate that rotary motion significantly suppresses negative lift during the upstroke. In addition, releasing the rotary degree of freedom alters vortex dynamics, shifting the leading-edge vortex core and affecting its structure during downstroke and upstroke. A reduction ratio of 28 is identified as optimal, yielding approximately 20% higher average lift compared to a reduction ratio of 24.5. Overall, this work facilitates the understanding for the FWR's dynamic equilibrium of rotary motion and offers valuable design guidance for further enhancing the lift performance of the FWR.