VELOCITY WAVES IN THE BOUNDARY LAYER DISTURBED BY WAKES OF NEGATIVE AND POSITIVE JETS IN ACCELERATING FLOW

Анотація

Experimental boundary layer investigation was performed for two values of velocity acceleration at the edge of layer-. The flow was disturbed by oncoming wakes from a pendulating upstream rod yielding negative and positive jets in turn (negative jet if the rod goes upwards making suction in boundary layer on the upper surface of the flat plate, positive jet — the rod goes downward). Velocity traces and phase-averaged velocity traces were obtained using periodic phase mark. Mean velocity profiles and longitudinal distribution of mean or integral parameters stayed close to laminar pattern. The shape of wakes on velocity traces were these same regardless of jet direction. However-, past negative jets velocity waves were observed on velocity traces. They were placed in the damped region of Tollmien-Schlichting waves. Past positive jets there was no evidence of velocity waves, which is main difference between influence of both kind of jets on boundary layer development.