A comparison of turbulence model results with DNS for smooth and stepped rotating cylinder electrodes

Jacobs, Carolyn (2005). A comparison of turbulence model results with DNS for smooth and stepped rotating cylinder electrodes B.Sc Thesis, School of Engineering, The University of Queensland.

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Author Jacobs, Carolyn
Thesis Title A comparison of turbulence model results with DNS for smooth and stepped rotating cylinder electrodes
School, Centre or Institute School of Engineering
Institution The University of Queensland
Publication date 2005-01-01
Thesis type B.Sc Thesis
Supervisor Professor Klaus Bremhorst
Total pages 94
Language eng
Subjects 0913 Mechanical Engineering
Formatted abstract

This thesis is an investigation into computational modelling of the Rotating Cylinder Electrode (RCE) and the Stepped Rotating Cylinder Electrode (SRCE).

The Rotating Cylinder Electrode is one of the most widely used methods of producing turbulent flow for the study of corrosion as the flow reaches the turbulent region at quite low rotational speeds. The stepped rotating cylinder was developed at the University of Queensland as a means of investigating erosion-corrosion in disturbed flow [Nesic et al., 2000].

Previous work on the stepped rotating cylinder includes a number of experimental studies and Direct Numerical Simulation (DNS). DNS has also been recently completed for the rotating cylinder electrode. However, DNS is computationally quite expensive for such a complex flow pattern as that produced by the SRCE. Therefore, it becomes necessary to discover an alternate computational method of generating suitably accurate flow data.

The majority of turbulence models used today have difficulty simulating the complex flows involved in flow separation and reattachment because of limitations to the accuracy of the wall functions used in the near-wall region. Use of the Reynolds Averaged Navier-Stokes equations (RANS) with various turbulence models will be tested in this thesis with the aim to produce comparable descriptions of the flow, but at much lower computational cost. The thesis will also investigate the near-wall flow around the rotating cylinder electrode using the same models.

A number of common turbulence models were selected for investigation. These models were the standard k-ε model, the realizable k-ε model, the RNG k-ε model, the standard k-ω model, the SST k-ω model, and the Reynolds Stress model (RSM).

Two-dimensional models of the rotating cylinder geometry and the stepped rotating cylinder geometry were produced using the GAMBIT pre-processor and the computational fluid dynamics (CFD) package FLUENT. The near-wall velocity profile, the wall shear stress and the near-wall turbulent kinetic energy profile were compared to the DNS data for the RCE. For the SRCE simulations, the mean velocity profile, the location of the reattachment point and the near-wall turbulent kinetic energy from the turbulence model simulations are compared with the DNS data provided in Yang et al. [2003] in order to determine the most suitable model for this complex flow pattern.

Simulation of the flow for both geometries proved to be difficult to achieve. Meshing of the rotating cylinder electrode was quite simple, but for the stepped rotating cylinder it proved to be difficult to get the mesh to leave the step surface parallel. The flow over the step also had difficulty forming the recirculation pattern expected from the DNS data.

For the rotating cylinder electrode flow, the most suitable turbulence model was found to be the standard k-ε model. Of the six models, the RNG k-ε model proved to be the most suitable for the SRCE geometry. The k-ω turbulence models produced quite poor results for the both rotating cylinder flows. The realizable k-ε model also had difficulty modelling the complex recirculation of the SRCE.

Keyword Rotating Cylinder Electrode (RCE)
Stepped Rotating Cylinder Electrode (SRCE)
Additional Notes * Mechanical engineering undergraduate theses. Sem 2, 2005

Document type: Thesis
Collection: UQ Theses (non-RHD) - UQ staff and students only
Citation counts: Google Scholar Search Google Scholar
Created: Fri, 10 May 2013, 21:29:15 EST by Mr Yun Xiao on behalf of Scholarly Communication and Digitisation Service