Effect of spanwise-uniform streaks on the transition in the boundary layer on a swept wing at elevated vorticity of the flow

The influence of spanwise-uniform roughness elements (streaks) on the transition to turbulence in the boundary layer on a swept wing with domination of crossflow instability in the presence of unsteady and steady free-stream vortices is studied. The measurements are performed for rectangular (in the plane parallel to the flow and normal to the wall) roughness elements shaped as streaks of different heights, which have two different widths in the chord direction. The experiments are performed in a low-turbulence wind tunnel at low subsonic velocities of the incident flow with the use of hot-wire anemometry. The studies are conducted in the range of unit Reynolds numbers (based on the streamwise component of velocity at the boundary layer edge at the beginning of the rough surface region) $0{,}687\cdot 10^6\div 1{,}568\cdot 10^{6}$ 1/m. The results are obtained in 76 regimes of measurements for two types of free-stream vortex disturbances generated by two turbulizing grids: with domination of unsteady disturbances and combination of steady and unsteady disturbances.