Experimental Investigation of Unsteady Aerodynamic Forces on Airfoil in Harmonic Translatory Motion

摘要

The present paper describes the main results from an experimental investigation of the unsteady aero- dynamic forces on a NACA 0015 airfoil subject to 1-degree-of-freedom (DOF) harmonic translatory motion. The focus of the experimental investigations was to determine the factors that influence the aerodynamic damping of harmonic translatory motion. The maximum negative aerodynamic damping was found to take place at moderate stall and an incidence of about 15o, at a movement direction close to the chordwise direction. Up to three distinctively different stall modes (multiple stall) were observed near maximum lift for both stationary and moving airfoil configurations. The mean as well as the dynamic characteristics of the different stall levels were found to differ from each other. An investigation of the negative aerodynamically damped cases showed that the damping decrease as the reduced frequency is decreased. Comparison between the experimental data, 2D Navier-Stokes computations and two commonly used dynamic stall models reveal that all models failed to reproduce the dynamic characteristics of the flow for incidences above maximum lift, however the Navier-Stokes computations generally captured the dynamic features more correctly than the dynamic stall models.