Eur. Phys. J. E (2018) 41: 125
https://doi.org/10.1140/epje/i2018-11736-2

Regular Article

Rough-wall turbulent Taylor-Couette flow: The effect of the rib height

¹ Physics of Fluids, Max Planck Institute for Complex Fluid Dynamics, MESA+ institute and J. M. Burgers Center for Fluid Dynamics, University of Twente, P.O. Box 217, 7500 AE, Enschede, The Netherlands
² Dipartimento di Ingegneria Industriale, University of Rome “Tor Vergata”, Via del Politecnico 1, 00133, Roma, Italy
³ Center for Combustion Energy and Department of Energy and Power Engineering, Tsinghua University, 100084, Beijing, China
⁴ Max Planck Institute for Dynamics and Self-Organization, 37077, Göttingen, Germany

^* e-mail: rubenverschoof@gmail.com
^** e-mail: chaosun@tsinghua.edu.cn
^*** e-mail: d.lohse@utwente.nl

Received: 2 May 2018
Accepted: 26 September 2018
Published online: 22 October 2018

Abstract

In this study, we combine experiments and direct numerical simulations to investigate the effects of the height of transverse ribs at the walls on both global and local flow properties in turbulent Taylor-Couette flow. We create rib roughness by attaching up to 6 axial obstacles to the surfaces of the cylinders over an extensive range of rib heights, up to blockages of 25% of the gap width. In the asymptotic ultimate regime, where the transport is independent of viscosity, we emperically find that the prefactor of the scaling (corresponding to the drag coefficient being constant) scales with the number of ribs and by the rib height . The physical mechanism behind this is that the dominant contribution to the torque originates from the pressure forces acting on the rib which scale with the rib height. The measured scaling relation of is slightly smaller than the expected scaling, presumably because the ribs cannot be regarded as completely isolated but interact. In the counter-rotating regime with smooth walls, the momentum transport is increased by turbulent Taylor vortices. We find that also in the presence of transverse ribs these vortices persist. In the counter-rotating regime, even for large roughness heights, the momentum transport is enhanced by these vortices.