Boundary-layer transition on a rotor blade measured by temperature-sensitive paint, thermal imaging and image derotation

Transition measurements using temperature-sensitive paint (TSP) and infrared (IR) imaging are shown for a model-scale rotor blade using derotation by an axial rotating mirror. Measurements were performed on a modified NACA0015 blade model by different angles of attacks at low-speed conditions. The effective angle of attack was computed from the geometric angle of attack and the downwash measured using particle image velocimetry (PIV) and from numerical computations by an actuator disc method based on blade element theory. The transition over a laminar separation bubble was detected in TSP and IR results for all investigated angles of attack. Additional two-dimensional high-resolution PIV measurements were performed near the surface of the modified NACA0015 model. The mean point of laminar separation (LS) and mean point of turbulent reattachment (TR) were extracted from TSP results. The single transition point was set at the 50 % between LS and TR and compared with predictions from Euler-boundary-layer code with an envelope-e^N transition prediction.