Recent Wind Tunnel Tests With HLFC Flat Plate

HLFC tests with a modular flat plate model are conducted in the DNW-NWB wind tunnel in Braunschweig (Germany). For boundary layer stabilization, multiple suction panels are inserted at various positions in the model. This way, transition Reynolds numbers are increased from around 3 million without suction to more than 15 million in cases with four sequential suction areas and non-suction elements in between. Transition positions are determined using infrared thermography, whereas boundary layer profiles and perturbation amplitudes are measured with a hot-wire probe as well as hot-film surface sensors. Perturbations at multiple streamwise positions are compared to Linear Stability Theory predictions for HLFC cases and natural transition cases. Directly above a suction surface, very good agreement between LST and amplitudes measured with the hot-wire is observed, whereas downstream the suction region, a noticeable discrepancy is found. This article presents the major findings from the experiments. The work was part of the DLR project LamTA and the Cluster of Excellence SE2A from TU Braunschweig.