Application of the wide-field shadowgraph technique to rotor wake visualization

This paper reviews the wide-field shadowgraph technique and its application to the visualization of rotor wakes. In particular, it discusses current experimental methods and data-reduction requirements. Sample shadowgraphs are presented. These include shadowgraphs of model-scale helicopter main rotors and tilt rotors, and full-scale tail rotors, both in hover and in forward flight. Notation CT = rotor thrust coefficient h = rotor distance from ground plane, m Mt = tip Mach number R = rotor radius, m r = radial distance, m z = axial distance, m kt = advance ratio = rotor solidity