The effect of pressure gradient and a non-adiabatic surface on boundary layer transition investigated by means of TSP

Abstract

The influence of streamwise pressure gradient and a non-adiabatic wing surface on boundary layer transition was experimentally investigated at the DNW-KRG blow-down wind tunnel facility in Göttingen, Germany. Boundary layer transition was detected non-intrusively by means of the Temperature-Sensitive Paint technique. A new wind tunnel model was designed with the aim of systematically investigating the influence of streamwise pressure gradient and a non-adiabatic wing surface, including Reynolds number effects and Mach number effects, on boundary layer transition. The model was tested at high Reynolds numbers and at a high subsonic Mach number. Favorable, neutral, and unfavorable streamwise pressure gradients were considered and various temperature differences between flow and model surface were implemented. More pronounced negative streamwise pressure gradients and surface temperatures closer to the adiabatic wall temperature were shown to stabilize the boundary layer and allowed larger transition Reynolds numbers to be achieved. The resulting effect of the coupling of streamwise pressure gradient and a non-adiabatic wing surface was found to be strongly dependent on the considered stability situation. The favorable effect on boundary layer transition of surface temperatures closer to the adiabatic wall temperature was shown to be more pronounced for stability situations characterized by a markedly negative pressure gradient.