Experiments and simulations on short-wave instabilities in helical vortices

Abstract Short-wave instabilities of helical vortices are investigated experimentally using a one-bladed rotor and numerically with a spectral/spectral-element code. Certain rotor flow configurations, defined by the Reynolds number (Re) and tip speed ratio ( λ ), exhibit short wave deformations of the vortex core. Increased λ or decreased Re lead to earlier and more pronounced perturbations, possibly due to enhanced helix loop interaction or increased turbulence from flow separation. The perturbations display wavelengths longer than expected for elliptic instability, possibly due to the specific velocity profiles of the vortices in this study. Numerical simulations based on measured velocity profiles align well with experiments. The exact origin of these instabilities remains uncertain, with possible mechanisms including elliptic, curvature/torsion, or swirling jet instabilities.