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The application of Hybrid Laminar Flow Control (HLFC) by suction of the boundary layer has the potential to delay the location of laminar-turbulent transition and, hence, reduce drag caused by skin friction. Up to now most of the research on HLFC has been performed at low Reynolds and Mach numbers. To investigate the technology at flow conditions relevant for today's commercial flight additional studies at higher Reynolds numbers are required. At high Reynolds numbers the major challenge is an appropriate scaling of the perforation used for sucking the boundary layer, leading to very small perforation diameters of only a few microns. In this paper, the applicability of HLFC on a two-dimensional wind tunnel profile is investigated in the cryogenic Pilot European Transonic Windtunnel (PETW). The natural laminar-turbulent boundary-layer transition is visualized with temperature-sensitive paint (TSP). The transition locationobtained with an active HLFC system is compared to a reference case without HLFC for different angles of attack, Reynolds numbers, free stream Mach numbers and suction rates. Furthermore, the influence of the perforation diameter is also investigated. Results of an alternative approach, using a sintered porous material instead of a regular perforation for sucking the boundary layer, are also presented.

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