Experimental investigation of step-induced transition delay by means of suction

Abstract

The influence of different suction rates on step-induced boundary-layer transition has been experimentally investigated in the Cryogenic Ludwieg-Tube Goettingen at large chord Reynolds numbers (up to 16 Million), Mach numbers from 0.35 to 0.77 and various stream wise pressure gradients by means of Temperature-Sensitive Paint (TSP). A surface imperfection, implemented as combination of gap and forward facing step, caused transition to occur at a location more upstream than in case of a smooth surface (i.e. without gap and step). It was found that suction, achieved passively by exploiting the pressure difference between upper and lower side of the model, induced a movement of transition to a more downstream location than on the smooth configuration at the same test conditions. Thus, the effect of suction was to even overcompensate the adverse effect of the combination of gap and forward-facing step on boundary-layer transition. This effect was enhanced for higher suction rates.