Stability characteristics of the boundary layer developing on a flat plate with spanwise sinusoidal corrugations

In low disturbance environments boundary layer transition is tipically driven by Tollmien-Schlichting (TS) waves. In passive controls aimed at transition delay, minimal geometric modifications are introduced to attenuate TS waves. Following the strategy called "spanwise mean velocity gradient" (SVG, see [1]), TS waves can be attenuated by inducing appropriate spanwise modulations of the streamwise velocity. A number of successful examples of SVG have been documented in the literature, and most of these are related to the use of miniature vortex generators (MVGs, see [2]).

In the present investigation the SVG method is implemented by small-amplitude spanwise sinusoidal corrugations of the wall of a nominally flat plate. Compared to localised controls, such as those based on MVGs, the strategy proposed here has several advantages, i.e. it is less intrusive, easier to implement in practice, and and has a more prolonged effect on the flow in the streamwise direction. This specific control has been proposed and experimentally investigated by Prof. J.H.M. Fransson and co-workers at KTH Mechanics of Stockholm [personal communication]. 

The characteristics of flow fields computed by dedicated simulations are discussed here for a wide range of free parameters of the geometry. In addition, the effect of the control on the spatial stability curves is shown and the most effective geometries for influencing transition are identified.

 [1] Shahinfar, S., Fransson, J. H. M., Sattarzadeh, S. S., Talamelli, A., 2013, J. Fluid Mech., 733, 1--32.

 [2] Shahinfar, S., Sattarzadeh, S. S., Fransson, J. H. M., Talamelli, A., 2012, Phys. Rev. Lett. 109, 074501.