Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session F26: General Fluid Dynamics: Drag Reduction, Obstacles and Constrictions
8:00 AM–10:10 AM,
Monday, November 19, 2018
Georgia World Congress Center
Room: B314
Chair: Jonathan Clausen, Sandia National Lab
Abstract ID: BAPS.2018.DFD.F26.1
Abstract: F26.00001 : Bubbly drag reduction using a superhydrophobic inner cylinder in Taylor-Couette turbulence *
8:00 AM–8:13 AM
Presenter:
Pim A. Bullee
(University of Twente)
Authors:
Pim A. Bullee
(University of Twente)
Ruben A. Verschoof
(University of Twente)
Dennis Bakhuis
(University of Twente)
Rodrigo Ezeta
(University of Twente)
Sander G. Huisman
(University of Twente)
Chao Sun
(Tsinghua University)
Rob G. H. Lammertink
(University of Twente)
Detlef Lohse
(University of Twente)
We investigate the drag of a highly turbulent flow over a non-wetting surface of micro-scale roughness. The Taylor-Couette geometry is used, allowing accurate drag and flow measurements. The inner cylinder is coated with a rough, hydrophobic material, whereas the outer cylinder is kept smooth. We vary the void fraction of air α present in the working fluid to introduce bubbles to the flow. For smaller volume fractions of air, up to α ≤ 2%, we observe that the increased surface roughness from the coating increases the drag. For larger fractions of air, α > 2%, the drag decreases compared to a smooth hydrophilic, uncoated cylinder using the same volume fraction of air. This suggests that two mechanisms play a role: the roughness invokes a shift in the log-layer – resulting in an increase in drag – and the more effective drag-reducing mechanism of the superhydrophobic surface. The balance between these two effects determines whether bubble drag reduction is more effective when using a superhydrophobic surface compared to using a smooth hydrophilic surface.
*NWO-TTW project 14504 (Bullee), NWO-TTW project 13265 (Verschoof), NWO MCEC project (Huisman), NWO-TTW project 12ULT01 (Ezeta) and VIDI grant 13477 and Natural Science Foundation of China under grant 11672156 (Sun and Bakhuis).
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2018.DFD.F26.1
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