• Wavy-surface
• Stability
• Nek5000
• DNS

In the present thesis it is analyzed the possible effectiveness of properly designed wavy walls as a control device of laminar-to-turbulent transition. The potential advantage is the drastic reduction of the friction drag.
The configuration considered here has been previously investigated experimentally at KTH Mechanics by Prof. Fransson, showing evidence of transition delay. The present investigation is aimed at identifying the stabilization mechanisms observed in the experiments.
The flow in absence of external disturbances has been simulated using the open-source code Nek5000 and this simulation aspect has been developed in the first part of the thesis.
The remaining part focuses on the study of Tollmien-Schlichting (TS) waves evolution in the considered boundary layer because TS waves are responsible of transition to turbulent regime in low disturbance environments. This stability analysis has been carried out using ad-hoc numerical codes and by carrying out local temporal and spatial stability analysis. The results are condensed into neutral stability curve and into spatial growth rate graphics of TS waves, both of them compared to the corresponding uncontrolled case, i.e. Blasius boundary layer.
The results of the analysis show that the transition delay previously observed in experiment appears in qualitative agreement with stability analysis. Furthermore, in preliminary way we can state that global properties of the controlled flow stability are improved even if still to be elaborated.