Michea Giuni

Analytical/Experimental Comparison of the Axial Velocity in Trailing Vortices

The axial velocity of a vortex is a parameter which is known to be strongly related to the vortex breakdown, yet to date a complete description of its physical origins has not been achieved. A series of experiments studying the vortex trailed from a NACA 0015 wing using stereoscopic particle image velocimetry is presented and the axial velocity studied in detail. The problem of centering the instantaneous vector fields is addressed showing a high sensitivity of the results from the centering method which is adopted. It is shown that a strong axial velocity excess exists and a linear relationship between the axial velocity and a circulation parameter of the vortex is shown. The experimental data are compared with the analytical descriptions of the velocity in the centre of a simplified vortex giving new insights of the viscous effects in the development of the axial flow.

Investigation of a Trailing Vortex Near Field by Stereoscopic Particle Image Velocimetry

High spatial resolution experiments in the near field of a trailing vortex using a SPIV technique have been carried out. A particular attention on the measurement technique is presented highlighting the importance of the laser pulses delay between the two frames in a double-frame/single-pulse method and of the images processing characteristics in the evaluation of velocity profiles and turbulence quantities. The number of samples needed for the statistical convergence of the mean flow and the turbulent quantities has also been found. A study on the vortex aperiodicity correction method has revealed how the instantaneous vector fields centering affects the velocity profiles across the vortex. The importance in the choice of the vortex quantity which is used for the vortex centre detection is presented.