Transition Detection and Skin-Friction Extraction from Temperature-Sensitive Paint Data

DLR and CNR-INM cooperate since several years on the application and further development of the Temperature-Sensitive Paint (TSP) measurement technique for boundary-layer transition detection and skin-friction diagnostics. The common efforts originally focused on underwater experimental research on boundary-layer transition, separation and reattachment over bluff and slender bodies, with the recognized successful development and application of methodologies to optically determine skin-friction fields from TSP data, as confirmed by common INM-DLR publications [1-5]. The analysis of the TSP data enabled to study in detail the random bursting and evolution of turbulent, wedge- shaped events characterizing the laminar separation bubble over the suction side of a NACA 0015 airfoil model at both moderate Reynolds number and angles of attack [3]. The experimental observations motivated the recent numerical investigation of the flowfield by means of Large Eddy Simulations (LES), which confirmed the conjectured role of flow structures and further shed light on the flow evolution at these transitional conditions [6]. Another focus of the DLR-INM cooperation in the recent years has been on the investigation of boundary-layer transition, separation and reattachment in a compressible air flow (freestream Mach number up to 0.75) at a chord Reynolds number of 10 million [7]. In this experimental campaign on a supercritical airfoil model, boundary-layer transition was examined for a variety of pressure distributions, including cases with laminar separation bubbles and shock-wave / boundary-layer interaction.