title: Drag reduction in bubbly Taylor-Couette turbulence.
abstract: In Taylor-Couette flow the total energy dissipation rate and therefore the drag can be determined by measuring the torque on the system. We do so for Reynolds numbers between Re=7 x 10(4) and Re=10(6) after having injected (i) small bubbles (R=1 mm) up to a volume concentration of alpha=5% and (ii) buoyant particles (rhop/rhol=0.14) of comparable volume concentration. In case (i) we observe a crossover from little drag reduction at smaller Re to strong drag reduction up to 20% at Re=10(6). In case (ii) we observe at most little drag reduction throughout. Several theoretical models for bubbly drag reduction are discussed in view of our findings.
authors.affiliation: Department of Applied Physics, University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands. t.h.vandenberg@tnw.utwente.nl
authors.forename: Thomas H
authors.initials: TH
authors.lastname: van den Berg
authors.forename: Stefan
authors.initials: S
authors.lastname: Luther
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Lathrop
authors.forename: Detlef
authors.initials: D
authors.lastname: Lohse