Experimental investigation of cross-flow instability in swept-wing boundary layers

Stationary cross-flow instabilities and transition pattern in the boundary layer of a 45° swept wing with and without 3D artificial leading edge roughness were investigated by sublimation method. For the model without artificial roughness, straight transition lines behind the minimum pressure point which are dominated by T-S instabilities appeared in the Reynolds number range of 5.50⁵~1.65⁶. When Re≥1.38×10⁶, traces of the most amplified stationary cross-flow waves were detected, and 3.5-4.0 mm spacing stripes agreed quite well with the results of linear stability theory. The ex-treme sensitivity of the stationary disturbance to leading edge roughness is verified at Re=1.65⁶. In order to modify the most amplified cross-flow waves which usually dominate transition on the swept wing of an aircraft, different spacing leading edge roughness were applied. At Re=1.38⁶, 2.5 mm spacing roughness suppressed the most amplified waves and showed the potential ability to suppress the transition dominated by stationary cross-flow waves. In addition, half of the input wavelengths which attribute to harmonics appeared when 6.0~8.0 mm spacing roughness printed.