Wide-field shadowgraphy of tip vortices from a helicopter rotor

The vortex trajectory and vortex wake generated by helicopter rotors were visualized using a wide-field shadowgraph technique. Tip vortex trajectories were visible in shadowgraphs for a range of tip Mach numbers of 0.38-0.60. The effect of the angle of attack was substantial. The theoretical analysis of the visibility was carried out for a rotating blade. This analysis demonstrated that the visibility decreases with increasing dimensionless core radius (r sub(0)/c) and increases with increasing tip Mach number. Based on this investigation, it is concluded that the wide-field shadowgraph flow-visualization technique should be feasible to study the flowfield generated by a large main rotor in a wind tunnel and in an outdoor full-scale test stand.