The process of laminar-turbulent transition consists of three stages: receptivity, linear eigenmode growth and nonlinear breakdown to turbulence. At the second stage, the interaction between Tollmien–Schlichting waves and base flow distorted by localised roughness elements generally prompts the onset of laminar-turbulent transition. For a small localised roughness element, the interaction has been addressed in our JFM paper. Recently, the interaction between Tollmien–Schlichting waves and base flow distorted by 3D localised roughness elements has also been studied. Here, we show an animation of laminar-turbulent transition which is simulated by nektar++ 2.5D DNS:

Acknowledgements: 

• Innovate UK
• United Kingdom Turbulence Consortium (UKTC)
• EPSRC: Developments Underpinning Laminar Flow Control (LFC-UK)