Experimental study of bump effects on boundary ­layer transition in compressible high Reynolds number flow

Abstract

The influence of surface bumps on boundary-layer transition was experimentally investigated in the present work. The experiments were conducted in a (quasi-) two-dimensional flow at freestream Mach numbers up to M = 0.77 and chord Reynolds numbers up to Re= 10 millions in the low-turbulence Cryogenic Ludwieg-Tube Göttingen. Various streamwise pressure gradients relevant for natural laminar flow surfaces were implemented. An available two-dimensional flat-plate model was modified to accept exchangeable inserts on the model upper side. The quasi-two-dimensional surface bumps were manufactured on the inserts and had a sinusoidal shape in the streamwise direction. Three bumps with different height-to-length ratio were examined. The model was equipped with temperature-sensitive paint for non-intrusive transition detection and with pressure taps for the measurement of the surface pressure distributions. Natural transition was shown to occur at a more upstream location with increasing bump height-to-length ratio.