EXPERIMENTAL APPROACH TO INVESTIGATION OF EXCITATION OF INSTABILITY MODES IN A SWEPT-WING BOUNDARY LAYER AT SCATTERING OF FREESTREAM VORTICES ON SURFACE NONUNIFORMITIES

Receptivity is the very first stage of the laminar-turbulent transition which responsible for conversion of external environmental disturbances to initial eigen boundary-layer waves. In order to improve the understanding of this problem the project 'RECEPT ' was initiated in 201 1 under the 7'h Framework Programme (FP7). According to the project it was planned to investi-gate the receptivity of a boundary layer on a 35 " swept wing due to scattering of a free-stream vortices on an airfoil surface non-uniformities both experimentally and theoretically. For accu-rate quantitative measurements of receptivity characteristics, the experiments supposed to be performed at fully controlled experimental conditions including controlled surface non-uniformities and free-stream disturbances with spanwise orientation of the vorticity vector. The measurements planned to be performed at two angles of attack:-5 (experiments 'A ' and 'C') and +1.5 " (experiments 'B'). In the experiments 'A ' and 'C ' the cross-flow instability dominat-ed in the flow, while in experiments 'By the Tollmien-Schlichting instability was predominant. The experimental set-up was adjusted in a way that the excited harmonic free-stream vor-tex street swept just above the boundary layer edge. At nondimensional chordwise coordinate x/C = 0.15 it scattered on (interacted with) a streamwise localized controlled surface non