Bubbly Turbulent Drag Reduction Is a Boundary Layer Effect
ORAL
Abstract
In turbulent Taylor-Couette flow, the injection of bubbles reduces the overall drag. On the other hand, rough walls enhance the overall drag. In this work, we inject bubbles into turbulent Taylor-Couette flow with rough walls (with a Reynolds number up to $4\cdot10^5$), finding an enhancement of the dimensionless drag as compared to the case without bubbles. The dimensional drag is unchanged. As in the rough-wall case no smooth boundary layers can develop, the results demonstrate that bubbly drag reduction is a pure boundary layer effect.
*The work is part of the research program of FOM, which is financially supported by NWO. It was also supported by the National Science Foundation of the U.S.
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