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

TL;DR

This study experimentally investigates vortex shedding from a pitching wing, analyzing vortex dynamics and moments using a physics-based partitioning method, revealing scaling laws and validating the method against direct measurements.

Contribution

It introduces a physics-based force and moment partitioning method (FMPM) to analyze vortex-induced moments from flow data, providing new insights into vortex dynamics and fluid damping.

Findings

Vortex circulation and formation time follow scaling laws based on shear-layer velocity.

FMPM-estimated moments correlate well with direct force measurements.

Vortex dynamics explain nonlinear fluid damping behaviors.

Abstract

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., J. Fluid Mech., vol. 923, 2021, R2). 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.