Instationäre Transitionsmessung mit neuartigen Messmethoden

Hot film anemometry, surface pressure analysis, and differential infrared thermography(DIT) were simultaneously applied for the detection of unsteady boundary layer transition on a pitching helicopter main rotor blade airfoil at M = 0.30 and Re = 1.8E6. Results are presented for test cases with periodic ramp motion and for cases with sinusoidal motion. Good agreement exists between the results of the different techniques. The transition points detected both by the pressure analysis and by the DIT are always located within the transition region measured by the hot film anemometry. The agreement is excellent for low pitch rates, with differences increasing for high pitch rates, leading to a maximum offset of x=c = 0.03 for transition occurring upstream of 30% chord. The influence of the pitching frequency on the transition movement is detected by the hot film anemometry and by the pressure analysis in the same manner, whereas the DIT results exhibit a stronger frequency effect and an additional offset in the hysteresis compared to the results of the other techniques.