DOI: 10.1615/TSFP6
EXPERIMENTS ON THE LATE STAGES OF BOUNDARY LAYER TRANSITION
RESUMO
Experiments were conducted with two, smooth hills, lying well within the boundary layer over a flat plate mounted in a wind tunnel. One hill was shallow, with peak height h = 1.5 mm and width C = 50 mm; the other, steep, with h = 3 mm, C = 30 mm. Since the hills occupied one-half of the tunnel span, streamwise vorticity formed near the hills' edge. At a freestream speed of 3.5 m/s, streaks formed, with inflectional wall-normal and spanwise velocity profiles, but without effecting transition. Transition, observed at 7.5 m/s, took different routes with the two hills. With the steep hill streamwise velocity signals exhibited the passage of a wave packet which intensified before breakdown to turbulence. With the shallow hill there was a broad range of frequencies present immediately downstream of the hill. These fluctuations grew continuously and transition occurred within a shorter distance.