Delay of boundary layer transition by means of miniature vortex generators

The efficacy of spanwise velocity gradients (SVGs) to damp the growth of Tollmien-Schlichting waves and thus delay transition has been shown numerous times. One efficient means to generate SVGs in the mean flow is by employing miniature vortex generators (MVGs), featuring a height of less than the boundary layer thickness, that create streamwise vortices which then cause stable streamwise streaks inside the boundary layer. By combining multiple MVGs to a spanwise array, periodic streaks in the base flow can be generated. Previous investigations have mainly focussed on blade-type MVGs, that are efficient in generating streaks and delaying transition, but sensitive in practical applications. In this study, a new geometry -- a triangular wedge -- is employed and the characteristics of this type of MVG are examined. Furthermore, it has been shown that the transition delay is effective only while the SVGs are present in the flow. Naturally, they will decay with the downstream distance and need to be augmented at some point, which can be done using a second array of MVGs. However, the exact properties (e.g. location, height) of the second array remain to be determined and will be assessed in this study.