Fin sweep angle does not determine flapping propulsive performance

Abstract

The importance of the leading-edge sweep angle of propulsive surfaces used by unsteady swimming and flying animals has been an issue of debate for many years, spurring studies in biology, engineering, and robotics with mixed conclusions. In this work, we provide results from three-dimensional simulations on single-planform finite foils undergoing tail-like (pitch-heave) and flipper-like (twist-roll) kinematics for a range of sweep angles covering a substantial portion of animals while carefully controlling all other parameters. Our primary finding is the negligible 0.043 maximum correlation between the sweep angle and the propulsive force and power for both tail-like and flipper-like motions. This indicates that fish tails and mammal flukes with similar range and size can have a large range of potential sweep angles without significant negative propulsive impact. Although there is a slight benefit to avoiding large sweep angles, this is easily compensated by adjusting the fin’s motion parameters such as flapping frequency, amplitude and maximum angle of attack to gain higher thrust and efficiency.

Flow-induced oscillations of pitching swept wings: stability boundary, vortex dynamics and force partitioning

“…(2013) ( and ), simulations of pitching swept wings by Visbal & Garmann (2019) ( to ) and simulations of fin-like pitch–heave swept wings by Zurman-Nasution et al. (2021) ( to ), where the spanwise flow has been shown to exist but to have no effect on the aerodynamic force. We also analyse aerodynamic forces for different sweep angles and other wing kinematics, and observe similar results (not shown in this paper).…”

“…2007; Borazjani & Daghooghi 2013; Bottom et al. 2016; Zurman-Nasution, Ganapathisubramani & Weymouth 2021), as well as on many engineered fixed-wing flying vehicles. It is argued that wing sweep can enhance lift generation for flapping wings because it stabilizes the LEV by maintaining its size through spanwise vorticity transport – a mechanism similar to the lift enhancement mechanism of delta wings (Polhamus 1971).…”

Rapid flapping and fibre-reinforced membrane wings are key to high-performance bat flight

“…Attempting to actively control the time-dependent muscle and digit activity would add significant complexity and uncertainty to our geometric and kinematic model of the wing. While omitting part of the biological system such as the body and secondary lifting surfaces certainly introduces errors, focusing on the dominant contributor to the propulsive force has been used in many successful numerical studies [25,26]. We, therefore, limit the current study to the handwing with inactivated digits and focus on the dynamic thrust and lift production and passive deformation of that structure.…”

Effect of aspect ratio on the propulsive performance of tandem flapping foils

“…Contemporary literature on finite wings of varying AR often focuses on single flapping configurations (Hammer, Garmann, & Visbal, 2021;Zhong, Han, Moored, & Quinn, 2021;Zurman-Nasution et al, 2021b) with only a few studies related to tandem arrangements (Arranz, Flores, & Garcia-Villalba, 2020;Jurado, Arranz, Flores, & García-Villalba, 2022). A key feature of the above is the presence of tip vortices that transform the 2-D wake into a complex chain of ring-like formations (Li, Pan, Zhao, Ma, & Wang, 2018;Shao et al, 2010).…”

“…These systems are often more agile, durable and efficient compared to conventional man-made propulsors (Weymouth, 2016). Thus, many studies have focused on the analysis of these biological configurations in terms of kinematics (Cimarelli, Franciolini, & Crivellini, 2021; Khalid et al., 2021), fluid–structure interaction (Kim, Hussain, & Gharib, 2013; Zurman-Nasution, Ganapathisubramani, & Weymouth, 2020) as well as the effects of planform geometry (Dagenais & Aegerter, 2020; Zurman-Nasution, Ganapathisubramani, & Weymouth, 2021b) and flexibility (Fernandez-Feria & Alaminos-Quesada, 2021; Shi, Xiao, & Zhu, 2020).…”