Browsing by Author "Schulz, Kai A."

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    Delay of laminar-turbulent transition by counter-rotating cylindrical roughness elements in a laminar flat plate boundary layer
    (2023) Römer, Tristan M.; Schulz, Kai A.; Wu, Yongxiang; Wenzel, Christoph; Rist, Ulrich
    Delaying laminar-turbulent transition in boundary layers is of great interest since the skin-friction coefficient can be reduced by up to one order of magnitude. In this experimental research, it is shown that counter-rotating cylindrical roughness elements are able to delay transition under realistic flow conditions. Evidence is given by the intermittency, evaluated from hot-film measurements in a laminar water channel. An increase in rotation speed results in a delay of transition of up to 6.5%in the center of the plate. This trend can be explained by the streaks amplified by the rotating cylinders, resulting in a damping of the fluctuation amplitude in the boundary layer. The advantage of this method is that the transition delay can be actively controlled with conventional cylindrical roughness elements.