Transition delay by introducing spanwise velocity gradients

For stabilizing a boundary layer it has been shown both numerically and experimentally that the control idea of introducing steady spanwise velocity gradients\footnote{Cossu, C., Brandt, L. {\emph{Eur. J. Mech./B Fluids}} {\bf{23}}, 815, 2004.} is far more effective than what could be foreseen. Different devices have been analyzed experimentally, which can modulate the boundary layer in a controlled way, and so far miniature vortex generators\footnote{Shahinfar, S., Sattarzadeh, S. S., Fransson, J. H. M., Talamelli, A. {\emph{Phys. Rev. Lett.}} {\bf{109}}, 074501, 2012.} have shown to be the most coveted for transition delay. Currently, a popular control device in the control community is the plasma actuator, which mainly has shown its potential for separation control, but lately also for transition delay. In a wind tunnel investigation at KTH, the plasma actuators have been tested in a configuration aimed at making use of above control idea and its potential for transition delay will be discussed.