Differential Infrared Thermography for Unsteady Boundary-Layer Transition Measurements

Unsteady laminar/turbulent boundary-layer transition, dynamic flow separation, and reattachment are of special interest in recent propeller and helicopter aerodynamics, since modern rotor blade design methodologies increasingly take dynamic characteristics into account. Sophisticated experimental techniques for the of the skin-friction distribution (thereby also detecting transition) have to be developed in order to improve and validate numerical prediction and design methods. The complex hot-film anemometry has successfully been used in order to investigate the boundary-layer transition on pitching airfoils and -scale helicopter rotor models in forward-flight configurations.