Visualization of Boundary-Layer Transition in a Cryogenic Wind Tunnel by Temperature-Sensitive Paint

Abstract

Temperature-sensitive paint (TSP) has been applied to boundary-layer transition detection in a cryogenic wind tunnel. Three TSP dyes, Ru (bpy), Ru (trpy) and Ru (VH127), were evaluated for a temperature range from 100 to 298 Kelvin using a LN2-cooled cryostat and a spectrofluorometer. It was found that TSP based on Ru (trpy) has the highest sensitivity among these three. We used epoxy-based sprayable paint as insulating material for a test model. No cracks appeared at cryogenic temperatures as long as the total thickness is kept less than 80 microns. To demonstrate the capability of this TSP/insulating-layer combination, we conducted a 2-D airfoil model test in NAL 0.1-m Cryogenic Transonic Wind Tunnel. Natural and forced transition patterns were successfully visualized using TSP at temperatures from 100 to 150 Kelvin.