Advanced Laminar Flow Control on a Swept Wing: Useful Crossflow Vortices and Suction (Invited)

Results of high-order direct numerical simulations are summarized for the evolution of crossflow disturbances in incompressible wing-generic boundary-layers with suction at the wall. The concept of smart suction, an adapted combination of the upstream-flow-deformation (UFD) technique and suction, is presented for laminar flow control. In the UFD technique, relatively tightly spaced, useful crossflow vortices are excited once, grow to nonlinearly large amplitudes due to primary instability, and deform the baseflow thus suppressing otherwise naturally growing, nocent vortices with larger spanwise spacing, and do not cause secondary instability that otherwise rapidly invokes turbulence. They can also be excited repeatedly by specially ordered (groups of) suction orifices, leading to suction with distributed flow deformation (DFD), termed DFD suction. Results for suction panels are shown that have a significantly better performance than the otherwise ideal homogeneous suction at the same suction rate. Pinpoint suction can be used to directly attack secondary instability of nocent crossflow vortices: suction underneath the high-shear layer region causing the secondary instability is found to significantly attenuate secondary instability up to complete suppression, at relatively low suction rates.