Non-adiabatic surface effects on step-induced boundary-layer transition at a subsonic Mach number

Abstract

The effect on step-induced transition of surface temperatures T w different from the adiabatic-wall temperature T0w has been investigated in this work. Experiments were conducted in a (quasi-) two­dimensional flow at a freestream Mach number of M = 0.35 and chord Reynolds numbers up to Re = 10 · 106 with various streamwise pressure gradients and wall temperature ratios T .JTaw· Sharp forward-facing steps were mounted on a spanwise-invariant wind-tunnel model and studied in the Cryogenic Ludwieg­Tube Göttingen. Transition was detected non-intrusively by means of the Temperature-Sensitive Paint measurement technique. A reduction of the wall temperature ratio had a favorable influence on boundary-layer transition induced by forward-facing steps up to a certain value of the relative step height h/61.h, although the increase in transition Reynolds number for a given reduction in T ,)T0w was smaller at la:ger values of h/61.h. Above a certain value of h/61.h, tne influence of a reduction in the wall temperature ratio on boundary-layer transition became dependent on the transition location measured at !arger T jT0w.