Distributed Excitation of Crossflow Waves Due to Scattering of Freestream Vortices by Surface Waviness

Abstract

The amount of quantitative experimental data, devoted to mechanisms of transformation of vortical free-stream disturbances into cross-flow (CF) instability modes is very restricted. The present experimental investigation is a continuation and subsequent development of studies [1, 2, 5, 6]. Problems of the localized vortical receptivity of a swept-wing boundary layer were examined previously for cases of scattering of freestream vortices by surface nonuniformities [5] and surface vibrations [6]. The distributed vortical receptivity concerning excitation of the CF-waves by streamwise freestream vortices on a smooth surface was investigated in [1, 2]. In the present study, the surface was not smooth but had controlled spanwise-uniform long-wavelength roughness (waviness). Based on a developed technique, values of coefficients of the distributed vortex-roughness receptivity are obtained experimentally for the first time. Dependences of these coefficients on parameters of the base flow instability, freestream vortices, and surface waviness have been investigated.