Near-wall investigation of laminar separation bubbles using the temperature sensitive single-shot lifetime method

Abstract

Laminar separation bubbles (LSB) develop at aerodynamically low Reynolds numbers, at which unmanned aerial vehicles, gliders and wind turbine blades operate and are thus of great scientific interest. They form when a laminar flow separates due to an adverse pressure gradient and transition to a turbulent flow, which enhances the wall normal momentum exchange, which can result in a reattachment. Its formation on the suction side of airfoils leads to drastic variations in drag, pitch moments and lift. During flight, a maneuverable aircraft experiences a wide range of free-stream conditions and it is therefore impervious to research the aerodynamical behavior in facilities that can produce a wide range of scenarios. As the separation bubble is usually quite thin, its analysis becomes challenging and the extraction of near wall flow features is often higly uncertain. The focus of this project is to assess if the footprints of the flow structures on the surface can be spatially and temporally resolved using the single-shot temperature sensitive lifetime method in an environment in which the less flexible intensity method cannot be employed. If the reliable measurement of the footprints becomes possible, this technique could provide many details which are hardly accessible to other experimental methods.