Bubbly turbulent drag reduction is a boundary layer effect.
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 x 10(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.
van den Berg
Thomas H
TH
Department of Applied Physics, IMPACT, and J.M. Burgers Center for Fluid Dynamics, Physics of Fluids Group, University of Twente, P.O. Box 217, 7500 AE Enschede, Netherlands.
van Gils
Dennis P M
DP
Lathrop
Daniel P
DP
Lohse
Detlef
D