Airfoil wake modification with Gurney flap at Low-Reynolds number

TL;DR

This study investigates how Gurney flaps modify the wake structures of low-Reynolds number airfoils, revealing wake modes and their impact on lift, with implications for optimizing flap use in aerodynamic performance.

Contribution

It provides a detailed classification of wake modes induced by Gurney flaps at low Reynolds numbers and examines three-dimensional effects on wake regimes.

Findings

Four characteristic wake modes identified (steady, 2S, P, 2P)

Wake classification diagram guides Gurney flap selection

Spanwise instabilities suppress 2P mode at high angles

Abstract

The complex wake modifications produced by a Gurney flap on symmetric NACA airfoils at low Reynolds number are investigated. Two-dimensional incompressible flows over NACA 0000 (flat plate), 0006, 0012 and 0018 airfoils at a Reynolds number of $Re = 1000$ are analyzed numerically to examine the flow modifications generated by the flaps for achieving lift enhancement. While high lift can be attained by the Gurney flap on airfoils at high angles of attack, highly unsteady nature of the aerodynamic forces are also observed. Analysis of the wake structures along with the lift spectra reveals four characteristic wake modes (steady, 2S, P and 2P), influencing the aerodynamic performance. The effects of the flap over wide range of angles of attack and flap heights are considered to identify the occurrence of these wake modes, and are encapsulated in a wake classification diagram. Companion three-dimensional simulations are also performed to examine the influence of three-dimensionality on the wake regimes. The spanwise instabilities that appear for higher angles of attack are found to suppress the emergence of the 2P mode. The use of the wake classification diagram as a guidance for Gurney flap selection at different operating conditions to achieve the required aerodynamic performance is discussed.