Suppression of crossflow-induced boundary layer transition on a swept wing by sinusoidal roughness elements

The crossflow instability is one of the main causes of the laminar-to-turbulent transition of the boundary layer around swept wings of aircrafts. Because it is dominant near the leading edge, the suppression or avoidance of this crossflow-induced transition is important for making a wide area of the upstream boundary layer laminar and reducing the total frictional drag on the wing. In this study, assuming the JAXA technical reference aircraft TRA2012A flying at Mach number 0.781, a DNS analysis of boundary layer transition is performed locally at a position on the airfoil where the pressure and velocity distributions are obtained by a global RANS analysis. Stability analyses of primary and secondary instabilities have been performed for this boundary layer, and the DNS reproduces turbulent transitions in a similar process. To suppress this transition, a sinusoidally deformed artificial roughness is placed near the leading edge. The linear growth rate of crossflow instability is strongly suppressed because of the mean flow distortion by the roughness, which indicates the possibility of avoiding the transition over over a wide area of wing surface.