Experimental investigation of active (dynamic) control of hydrodynamic instability in a two-dimensional boundary layer

Abstract

An experimental study has been made of the concept of controlling boundary layer transition by superposition of anti-phase disturbances on the Tollmien-Schlichting (TS) waves developing in the Blasius boundary layer over a flat plate. The Tollmien-Schlichting waves were excited artificially by periodic suction and blowing through a spanwise slot in the surface of the plate. The anti-phase waves were generated through a second slot downstream of the first one. Phase and amplitude of these waves were adjusted by hand to obtain minimum amplitude of the resulting flow disturbances downstream of the excitation region. TS waves with initial amplitudes of up to 1.7 % of free-stream velocity were investigated. The parameters of the flat plate and the other experimental conditions allowed to investigate the complete development of the TS waves. For comparison, amplitude and phase of the TS waves were measured by using a single hot-wire sensor — the primary TS wave, the anti-phase TS wave and the wave resulting from superposition of both. The aim of this work is to discuss problems in optimum abatement of TS waves with dependence on amplitude and Reynolds number.