Creation and conversion of wing-tip vortices

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This thesis offers analyses of the wing-tip dependent vortex roll-up process using stereoscopic PIV water-tunnel experiments. The investigations were executed at the Institute of Aerospace Systems (Institut für Luft- und Raumfahrtsysteme) at RWTH Aachen University, Aachen, Germany, between 2009 and 2015. Special attention is given to the variable axial velocity component at the center of the vortex and its sensitivity towards the wing-tip shape, wing-loading, and Reynolds number. In distinct cases an instable process can be observed during the roll-up process, which is triggered by a time-independent spiral-like nutation of the vortex axis, followed by core widening and axial velocity reduction. The swirl characteristics of different phases of vortex creation, dynamic unstable vortex conversion, and natural as well as stimulated vortex ageing are unified in a vortex life cycle envelope, intending to offer further understanding of vortex behavior.