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Session: Passive Wake flows
Session starts: Wednesday 05 November, 10:20
Presentation starts: 11:00
Room: Commission roon 2

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Fulvio Scarano (TU Delft - Aerospace Engineering)
Kushal Kempaiah (TU Delft - Aerospace Engineering)

Abstract:
The organisation of wall turbulence is altered when actuators produce spanwise forcing, which reduces skin friction drag. A turbulent boundary layer with mechanically oscillated wall is investigated with high-resolution planar PIV and tomographic PIV. The direct measurement of wall shear yields a 15% reduction. Tomographic PIV visualizes the three-dimensional organisation of low- and high-speed streaks, along with ejection events and hairpin packets. A conceptual model of the drag reduction mechanism is proposed, whereby hairpin auto-generation is inhibited by the tilting action at the tail of low-speed streaks. An array of AC-DBD plasma actuators is intended to surrogate the mechanical oscillation. The preliminary characterisation in quiescent flow returns high peaks of induced spanwise velocity. However, discrete wall jets erupting from the wall produce starting vortices, deemed detrimental for drag reduction.