Time Resolved Flow Field Investigations of Low Reynolds number Transient Maneuvers

Transient pitch and plunge maneuvers of low aspect ratio wings in a special low Reynolds number wind tunnel have been investigated by means of high speed Particle Image Velocimetry to analyze the leading edge vortex dynamics quantitatively. A specific requirement of the measurement was to design and apply an optical arrangement for the laser light sheet which moves with the wing so as to keep the light sheet in fixed position on the upper side of the model. This became necessary because of the low pulse energy of high speed lasers and the large amplitudes of motion. This paper shows the principle and the implementation of this particular set-up. The evaluation procedure shows some specific steps concerning the preprocessing, for example, mask generation and disparity correction. The temporally-resolved data sets enable a tracking of vortices and a detailed analysis of the leading edge vortex dynamics in terms of circulation build-up and convection velocity.