Wall-bounded turbulence with streamwise curvature

Pieter Berghout

Research output: ThesisPhD Thesis - Research UT, graduation UT

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Abstract

Mapping any given roughness geometry to its fluid dynamic behaviour has been hampered by the lack of accurate and direct measurements of skin-friction drag. Here the TC system provides an opportunity as it is a closed system and allows to directly and reliably measure the skin-friction. However, the wall-curvature potentially complicates the connection between the wall friction and the wall roughness characteristics. In this thesis we study the effects of curvature (first) and roughness (second) on TC turbulence.
We apply the idea of a Monin–Obukhov curvature length to turbulent TC flow. This length separates the flow regions where the production of turbulent kinetic energy is governed by pure shear from that where it acts in combination with the curvature of the streamlines. We demonstrate that for all Reynolds numbers and radius ratios, the mean streamwise and angular velocity profiles collapse according to this separation. We then develop the functional form of the velocity profile.
We finally investigate the effects of a hydrodynamically fully rough surface on highly turbulent, inner cylinder rotating, TC flow. We find that the effects of a hydrodynamically fully rough surface on TC turbulence, where the roughness height k is three orders of magnitude smaller than the Obukhov curvature length Lc, are similar to those effects of a fully rough surface on a flat plate turbulent boundary layer (BL). Hence, the value of the equivalent sand grain height ks, that characterizes the drag properties of a rough surface, is similar to those found for comparable sandpaper surfaces in a flat plate BL. Next, we obtain the dependence of the torque (skin-friction drag) on the Reynolds number for given wall roughness, and find agreement with the experimental results to within 7%.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • University of Twente
Supervisors/Advisors
  • Lohse, Detlef, Supervisor
  • Verzicco, Roberto, Supervisor
  • Stevens, Richard J.A.M., Co-Supervisor
Thesis sponsors
Award date15 Jan 2021
Place of PublicationEnschede
Publisher
Print ISBNs978-90-365-5101-4
Electronic ISBNs978-90-365-5101-4
DOIs
Publication statusPublished - 15 Jan 2021

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