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Response and Recovery of Turbulent Pipeflow Past Square Bar Roughness Elements

  • Author / Creator
    Goswami, Shubham
  • This dissertation looks at the response and recovery of turbulent pipeflow past square bar roughness elements with two heights at Reynolds numbers of 5000 and 156000. The response of turbulent pipeflow to multiple square bar roughness elements is also evaluated at the higher Reynolds number using different Reynolds-Average-Navier-Stokes (RANS) models. Two roughness heights are considered for this study based on their relative position inside the boundary layer: h/D = 0.05 and 0.1, where h is the bar height and D is the pipe diameter. A validation and verification analysis enabled creating a benchmark on the performance of different RANS-based turbulence models in simulating non-equilibrium wall bounded turbulent flows. Using k-epsilon RANS model, which performed the best in the benchmark performance study, the effects of multiple roughness elements are examined using two separation patterns: periodic and scattered. The flow response and recovery are evaluated based on the variations in the mean and turbulent fields. It is determined that the mechanism of recovery is prolonged in the pipeflow perturbed by smaller roughness element of height h/D = 0.05. Increasing the number of roughness elements further prolong the flow recovery until it becomes asymptotic with three periodically separated square bars. The separation pattern of roughness elements has a negligible effect on the overall turbulent pipeflow response and recovery at a high Reynolds number. This study is then extended to the examination of viscoelastic effects on the response and recovery of turbulent pipeflow past a single roughness element with two heights using the Finitely Extensible Non-linear Elastic-Peterlin (FENE-P) rheological model incorporated into Direct Numerical Simulations (DNS) at Reynolds number of 5000. These simulations revealed the importance of viscoelastic characteristics in significantly altering the overall flow response and recovery compared to Newtonian flow. The viscoelastic fluid properties correspond to a high polymer-additive concentration solution. For both bar heights examined here, the viscoelastic flow experiences significant reduction in the size of the recirculation region, which is also translated to a considerably faster recovery compared to the Newtonian flow. Moreover, the near-wall turbulence is reduced significantly due to the viscoelastic effects, which contributes to a lower wall friction, and thus, a lower drag.

  • Subjects / Keywords
  • Graduation date
    Fall 2020
  • Type of Item
    Thesis
  • Degree
    Master of Science
  • DOI
    https://doi.org/10.7939/r3-hgax-3316
  • License
    Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.