The Harmonic Pitching NACA 0018 Airfoil in Low Reynolds Number Flow

TL;DR

This paper examines the aerodynamic performance of the NACA 0018 airfoil under harmonic pitching at low Reynolds numbers, highlighting turbulence model limitations and the effects of oscillation frequency on flow behavior.

Contribution

It evaluates the effectiveness of the Transition SST turbulence model in low Reynolds number flows and compares dynamic flow predictions with XFOIL, focusing on applications in wind turbines.

Findings

Transition SST model struggles at low Reynolds numbers

Higher oscillation frequency captures dynamic hysteresis effects

XFOIL has limitations in modeling laminar-to-turbulent transition

Abstract

This study investigates the aerodynamic performance of the symmetric NACA 0018 airfoil under harmonic pitching motions at low Reynolds numbers, a regime characterized by the presence of laminar separation bubbles and their impact on aerodynamic forces. The analysis encompasses oscillation frequencies of 1 Hz, 2 Hz, and 13.3 Hz, with amplitudes of 4{\deg} and 8{\deg}, along with steady-state simulations conducted for angles of attack up to 20{\deg} to validate the numerical model. The results reveal that the Transition SST turbulence model provides improved predictions of aerodynamic forces at higher Reynolds numbers but struggles at lower Reynolds numbers, where laminar flow effects dominate. The inclusion of the 13.3 Hz frequency, relevant to Darrieus vertical-axis wind turbines, demonstrates the model's effectiveness in capturing dynamic hysteresis loops and reduced oscillations, contrasting with the \(k-\omega\) SST model. Comparisons with XFOIL further highlight challenges in accurately modeling laminar-to-turbulent transitions and dynamic flow phenomena. These findings offer valuable insights into the aerodynamic behavior of thick airfoils under low Reynolds number conditions and contribute to advancing the understanding of turbulence modeling, particularly in applications involving vertical-axis wind turbines.