Injection effect on two dimensional boundary layer

Abstract

This paper presents an experimental investigation to study the effect of injecting a secondary jet of slot width, t, into the main stream of a zero pressure gradient, two dimensional flow parallel to a flat test surface. The injection angle ( α) to the downstream of the main flow direction ( x) varies from 30° to 90°. The study covers a blowing ratio ( M) range of 1.5 to 4.2. Tests are conducted in a low speed, suction type wind tunnel. Measurements of the mean velocity profiles are obtained parallel to the flow direction ( x/t of 0 to 114) and normal to the flow direction ( y/t up to 20) with the origin at the slot downstream edge. Results are presented as dimensionless boundary layer displacement thickness and momentum thickness as δ 1/t and δ 2/t , respectively. Results indicate that the velocity profiles for α of 30° and 45° have local U max and U min for lower M values. Increasing M causes the U min to vanish gradually, and simultaneously, U max is shifted gradually away from the wall vicinity. For these angles, the δ 1/t and δ 2/t showed negative values. For α of 45° and above, a separation bubble is created downstream of the injection slot. For α of 60° and 90°, the flow that reaches the wall vicinity did not make up for the deficiency in the boundary layer except at the far end of the test surface for high values of M.