The influence of a non-adiabatic surface on boundary-layer transition induced by forward-facing steps

Abstract

The effect on step-induced boundary-layer transition of surface temperatures different from the adiabatic-wall temperature was investigated for a (quasi-) two-dimensional flow at a high subsonic Mach number and large Reynolds numbers. Sharp forward-facing steps were mounted on a flat plate and step-induced transition was studied non-intrusively by means of the temperature-sensitive paint technique. The experiments were conducted in the Cryogenic Ludwieg-Tube Göttingen with various streamwise pressure gradients and temperature differences between flow and model surface. A reduction of the ratio between surface and adiabatic-wall temperatures had a favourable influence on step-induced transition at low values of the step Reynolds number. However, at larger values of the step Reynolds number, the increase in transition Reynolds number for a given reduction in the wall temperature ratio was smaller. Transition was found to be insensitive to changes in wall temperature ratio for step Reynolds numbers above a certain value.