Airfoil wake modification with Gurney flap at Low-Reynolds number

摘要

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