Coated Hot-Film Sensors for Transition Detection in Cruise Flight

Abstract

In this paper results of wind-tunnel experiments and flight tests that demonstrate the effectiveness of coated multisensor hot-film arrays using constant current anemometry to determine boundary-layer transition under cruise conditions are presented. The study focuses on the analysis of several coating procedures, materials, and coating thicknesses to improve mechanical durability and signal quality. After several numerical simulations and environmental resistance tests, for example, in climate chambers and low-speed flight experiments, wind-tunnel experiments and flight tests at transonic speeds are carried out. The numerous experimental and numerical investigations and flight tests in cooperation with the Deutsche Airbus GmbH on a Beluga airplane (300-600ST) show a 1-μm parylene layer covering the extremely sensitive hot-film sensors and conducting paths to be sufficiently robust to stand the environmental conditions in cruise flight for several months. Furthermore, flight tests at transonic speeds on the Mystere Falcon 20 E5 at an altitude up to 30,000 ft and Mach numbers up to 0.79 are conducted in a joint project with DLR Oberpfaffenhofen. Modified wing models are mounted under both wings of the Falcon. The surfaces are instrumented with coated hot-film arrays using 128 sensors. The tests on the Falcon prove parylene coated hot-film sensors to still possess the sensitivity to locate transition under real flight conditions.