Numerical investigation of the design of transition delay devices for a Blasius boundary layer

A numerical investigation on transition delay devices for a Blasius boundary layer is presented. Recent studies have highlighted the advantages of using streamwise streaks generated by an array of appropriate counter-rotating vortices, placed outside the boundary layer in transition delay control methods. Also Direct Numerical Simulations (DNS) have been carried out to evaluate the effect of idealised pairs of Rankine vortices on the Blasius boundary layer transition, but no attention has not been paid to the devices which can generate such vortices. This thesis yet is focused on the design of physical winglets which have to generate patterns of streamwise vortices which have been shown to be successful in delaying transition. To generate these configurations, where streawise vortice are arranged in a periodic pattern, a series of various devices with different geometries, such as delta-shaped or rectangular winglets, has been analysed. At first a numerical low-cost computational campaign has been developed to identify the geometries of the devices which allow to generate a flow approximating the reference cases. Once the reference configurations have been recreated, the effect of the devices on the evolution of the boundary layer has been investigated by DNS. In this way it has been possible to study the far-wake evolution of the vortices, paying attention to the streaks generated and the effects they produce on the Blasius boundary layer. Finally, a comparison with the reference cases has been proposed to evaluate the effective agreement between the flow generated by the different devices tested in this work and the numerical reference configurations