Dynamics of a strake vortex interaction with the turbulent boundary layer of a two-element airfoil

Abstract

This paper deals with the interaction of a generic strake vortex with the turbulent boundary layer of a two-element airfoil. For this, an angle of attack study of the two-element airfoil as well as a displacement of the height of the vortex generator relative to the airfoil is experimentally investigated. In order to resolve the vortex dynamics, a time-resolved Stereo-PIV campaign is conducted within the subsonic wind tunnel of the Technical University Braunschweig at a Reynolds number of Re ≈ 2 Mio, based on the retracted chord of the airfoil. The underlying vortex dynamics are investigated by means of a vortex core tracking from the PIV plane. Additionally, a proper orthogonal decomposition (POD) and a high-order dynamic mode decomposition (HODMD) are applied as a modal analysis. The POD produces the well established dipole structures for the longitudinal vortex, which are associated with a coherent vortex movement. Within the analysis, equivalent structures are found within the HODMD results. In contrast to the isolated strake vortex configuration, the spectrum of the modes and the top modes are shifted towards lower frequencies. Additionally, a circular motion of the HODMD modes is established to be the source of the lateral or vertical displacement observed within the vortex meandering.