Force moment partitioning and scaling analysis of vortices shed by a 2D pitching wing in quiescent fluid

We experimentally study the dynamics and strength of vortices shed from a NACA 0012 wing undergoing sinusoidal pitching in quiescent water. We characterize the temporal evolution of the vortex trajectory and circulation over a range of pitching frequencies, amplitudes and pivot locations. By employing a physics-based force and moment partitioning method (FMPM), we estimate the vortex-induced aerodynamic moment from the velocity fields measured using particle image velocimetry. The vortex circulation, formation time and vorticity-induced moment are shown to follow scaling laws based on the feeding shear-layer velocity. The vortex dynamics, together with the spatial distribution of the vorticity-induced moment, provide quantitative explanations for the nonlinear behaviors observed in the fluid damping (Zhu et al. in J Fluid Mech, 923:R2, 2021). The FMPM-estimated moment and damping are shown to match well in trend with direct force measurements, despite a discrepancy in magnitude. Our results demonstrate the powerful capability of the FMPM in dissecting experimental flow field data and providing valuable insights into the underlying flow physics.

Automated summary

This study experimentally investigates the dynamics and strength of vortices shed from a NACA 0012 wing during sinusoidal pitching in quiescent water. The vortex trajectory and circulation are analyzed over a range of pitching frequencies, amplitudes, and pivot locations. By utilizing a physics-based force and moment partitioning method (FMPM), the vortex-induced aerodynamic moment is estimated from measured velocity fields. The results show that the vortex circulation, formation time, and vorticity-induced moment follow scaling laws based on the feeding shear-layer velocity. The study also demonstrates the capability of FMPM in dissecting experimental flow field data and providing insights into the underlying flow physics.