Leading Edge Vortex Dynamics of Airfoils, Pitching Continuously at High Amplitudes

TL;DR

This study numerically investigates the unsteady flow and leading edge vortex dynamics of a pitching NACA 0012 airfoil at low Reynolds number, analyzing how frequency and pivot location affect vortex behavior and aerodynamic forces.

Contribution

It provides a detailed quantitative analysis of LEV evolution during high amplitude pitching, highlighting the effects of frequency and pivot position on vortex dynamics and aerodynamics.

Findings

Higher pitching frequency delays LEV formation and increases lift and drag.

Pivot location influences the phase and magnitude of aerodynamic forces, especially at higher frequencies.

LEVs tend to merge at higher frequencies, affecting flow stability and force characteristics.

Abstract

Airfoils pitching in the stalled regime have been of keen interest in recent years due to their desirable aerodynamic force characteristics. In this study, we are numerically investigating the unsteady flow past a NACA 0012 airfoil under sinusoidally pitching motion, using a finite volume based sharp interface immersed boundary solver. The flow is investigated in the low Reynolds number regime (Re=3000) for reduced frequencies of 0.1 and 0.5, at three different pivot locations (c/3, c/2 and 2c/3 from the leading edge). The airfoil is subjected to sinusoidal oscillations with its incidence angle varying from 15o to 45o. Leading edge vortices (LEVs) that are formed during the pitching motion dictate the transient aerodynamic characteristics. The flow field data is used to identify individual LEVs in the flow field. The spatio-temporal evolution of LEVs in terms of their strengths are traced throughout the pitching cycle to obtain a quantitative estimate of its evolution. The effect of pivot location and pitching frequency on the vortex evolution and aerodynamic forces is investigated. Change in pitching frequency is found to have a drastic effect on the vortex dynamics. LEV formation is delayed to higher fractional times and LEVs are found to interact and merge into each other at higher frequencies. The maximum lift and drag are also found to increase with pitching frequency. Pivot location is found to have a higher influence on the magnitude and phase of aerodynamic coefficients at higher frequencies. However, at both frequencies, moving the pivot axis aftward is found to delay LEV evolution and cause a phase lag on the aerodynamic forces.