Transient, Three-Dimensional Disturbances Interacting with a High-Lift Airfoil - Wind Tunnel Experiments

Abstract

This publication presents experimental investigations on the aerodynamics of a highlift airfoil in disturbed inflow. Transient, three-dimensional disturbances are generated in a closed wind tunnel test-section. These disturbances are created by means of two vortex generating airfoils. The first creates quasi two-dimensional, transient, transversal vortices whereas the second airfoil generates a longitudinal wingtip vortex. Convecting along the test-section, these vortices interact with each other and with a two-element airfoil in high-lift configuration. Various measurement techniques, like Particle Image Velocimetry (PIV), time resolved static pressure measurements, measurements of the static pressure distribution of the high-lift airfoil, and time resolved Five-Hole-Probe (FHP) measurements of the induced disturbances are used to identify and characterize these interactions. These measurements are complemented by qualitative surface oilflow visualizations of the highlift airfoil. It is found that the interaction of the vortices with the high-lift airfoil exhibits a varying complexity with changing angle of attack. At zero incidence, the effective flow angles induced by the vortices prevail. For higher angles of attack, complex interaction effects can be observed in the time-resolving static pressure signals. By phase-locked PIV measurements, it can be shown that the flow field at the high-lift flap for small incidences is governed by the circulation effect of the main element rather than by the velocity effect of the passing vortices.