We study the effect of surface roughness on the laminar-turbulent transition phenomenon, with the ultimate engineering goal of predicting and controlling the transition process in the swept wings of subsonic aircrafts. The ability to achieve fully laminar wings and hence reduce skin friction drag in realistic flight conditions involves the necessity to understand the interaction between a pre-existing crossflow instability developing in a three-dimensional boundary layer and step excrescence. The research is primarily conducted numerically and theoretically by means of Direct Numerical Simulations (DNS) and stability analyses.

Casacuberta, J., Hickel, S., Westerbeek, S., & Kotsonis, M. (2022). Direct numerical simulation of interaction between a stationary crossflow instability and forward-facing steps. Journal of Fluid Mechanics, 943, A46. 

Casacuberta, J  Hickel, S  and Kotsonis, M. Mechanisms of interaction between stationary crossflow instabilities and forward-facing steps, AIAA 2021-0854. AIAA Scitech 2021 Forum. January 2021.

Casacuberta J, Groot K. J , Hickel. S and Kotsonis .M . Secondary instabilities in swept-wing boundary layers: Direct Numerical Simulations and BiGlobal stability analysis, AIAA 2022-2330. AIAA SCITECH 2022 Forum. January 2022.