Three-Dimensional Instabilities of Vortices on a Periodically Plunging Wing

Three-dimensional vortex instabilities are examined on a periodically plunging wing oscillating in a reduced frequency range of k = 0.5 to 3. Two values of the normalized peak-to-peak plunging amplitudes are tested (A/c = 0.1 and A/c = 0.5) at a Reynolds number based on the chord length of Re = 10,000. Leading-edge, trailing-edge and tip vortices are revealed via phase-averaged volumetric velocimetry measurements. Instabilities of the leading-edge vortices are found to initiate at the tip section. These instabilities grow to a helical pattern, similar to an m=1 mode. Tip vortices also show spiraling instabilities due to the interaction with the trailing-edge vortices. Plunging amplitude and plunging frequency are observed to have direct effect on the wavelength of the instabilities.