Low- and High-Speed Flight Experiments on Transition Detection

Abstract

This paper describes in-flight measurements in low- and high-speed experiments to investigate laminar-turbulent transition on airfoils. The low-speed experiments were carried out using a laminar wing glove for a sailplane. Highspeed experiments on an modified A320 hybrid laminar fin were conducted in close collaboration with Airbus. Different surface sensor measuring techniques (piezofoil, surface hot wires, wall microphones) were used in the lowspeedexperiments.Thepiezofoiltechniquewasappliedinthehigh-speedin-flightexperimentstoprovetheoperation robustness, the functional capability, durability, and reliability under atmospheric conditions in cruise flight on modern airplanes. All measuring techniques weresuccessfully implemented forthe particular taskandthe laminarturbulent transition was detected with a high degree of certainty. For the high-speed investigations a complete piezofoilsensorarraywasglueddirectly tothe finwithoutcausinganyinterferencebetweentheboundarylayer flow and the sensor foil. This technique therefore offered the good potential to detect transition in the boundary layer under flight conditions especially in high-speed tests.