The critical condition for turbulent contamination in a flat-plate boundary layer

Abstract

Lateral growth of turbulent wedge is examined experimentally in a flat-plate boundary layer at low Reynolds numbers. Turbulent wedge is generated by exciting hairpin vortices through a small hole at a location where the Reynolds number is subcritical. The lateral growth of turbulent wedge occurs at the momentum thickness Reynolds numbers above 170, with successive growth of low-speed streaks in the ambient laminar flow region. Beyond the critical Reynolds number for the lateral turbulent contamination, the lateral spacing of low-speed streaks newly generated is 45 in wall units using the friction velocity of Blasius flow at the stage of their first appearance and increases to that of the developed wall turbulence as the instability and breakdown of low-speed streaks develop. © 2011 The Japan Society of Mechanical Engineers.