EFFECT OF SPANWISE-UNIFORM STREAKS ON SWEPT-WING BOUNDARY LAYER WITH ENHANCED FREE-STREAM VORTICITY

The influence of spanwise-uniform roughness elements (streaks) on the laminar–turbulent transition in the boundary layer on a swept wing with predominance 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 chordwise 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) from \(0.687\cdot 10^6\) to \(1.568\cdot 10^{6}\) 1/m. The results are obtained in 76 regimes of measurements for two types of free-stream vortex disturbances induced by two turbulence-generating grids: with predominance of unsteady disturbances and combination of steady and unsteady disturbances.