Evolution of Tip Vortices Generated by Two Bladed Rotor in Hover at Early Wake Ages

In order to investigate change of vortex structures and its evolving processes, two dimensional LDV system was used for measurement of velocity vectors of tip vortex, and PIV system was also used for visualizations of tip vortex array for two bladed rotor, respectively. Experiments provided vortex locations, tangential and axial velocity components of tip vortex at six wake ages of 9.5, 10.5, 60.5, 99.5, 129.5, 169.5 and corresponded six wake ages shifted with 180 degrees per each. It was resulted that tip vortices generated by the first blade satisfy Landgrebe’s model for their vortex locations even after they were accelerated by the second blade in downstream. Tangential velocity components of tip vortices follow Vatistas’ n=2 model on both inside and outside regions of rotor slipstream without loss of vortex circulation. Axial velocity profiles revealed that there were small but significant perturbations just outside the primary vortex core which implies the second blade affects the wake substantially. It was also found that tip paths of each blade were not willing to be coincided intrinsically.