Instability of streaky structure in a Blasius boundary layer

Abstract

An experimental study was performed to analyze the stability of localized streaky structure in a Blasius boundary layer. An artificial streaky structure was created by using suction or blowing through a thin spanwise slot at the wall. The velocity gradient generated by the suction or blowing was controlled by a damper. The Reynolds number based on the displacement thickness delta(1) was Re-delta 1 = 280 at the slot. The behavior of the artificial streaky structure was scrutinized by damping the velocity gradient. It was found that the local streamwise and spanwise velocity gradients play a significant role in the formation of different types of instability. Artificial Tollmien - Schlichting ( T - S) wave packets were created by a loudspeaker to elucidate the interaction of the streaky structure with the T - S wave packets. The T - S wave packets imposed on the streaky structure become unstable when the frequency of the T S wave packets exceeds a certain critical frequency. The development of the T - S wave packets was investigated on the basis of the neutral stability curve.