Date of Award

3-24-2019

Publication Type

Master Thesis

Degree Name

M.A.Sc.

Department

Mechanical, Automotive, and Materials Engineering

First Advisor

David Ting

Second Advisor

Rupp Carriveau

Keywords

IDDES, LES, Torus, Turbulence, Vortex shedding, Wake structure

Rights

info:eu-repo/semantics/openAccess

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

Abstract

This work presents three papers, those are mainly focused on the numerical simulations in order to scrutinize the force characteristics, wake structures and turbulence properties of the flow past a torus. The first paper compares the performance of URANS, LES, and IDDES turbulence models for simulating the flow around a torus with an aspect ratio of 3, at the Reynolds number of 9000, in terms of accuracy and cost-effectiveness. URANS fails to capture the turbulent nature of the flow, albeit it reliably predicts the mean flow. IDDES is found to be the optimal approach for this problem. It is less computationally expensive compared with LES, while the results provided are in accordance with those for LES and the documented experiments in the literature. In the second paper, an LES approach is carried out to study the effects of torus aspect ratio (AR) on the flow characteristics at the Reynolds number of 9000. Three aspect ratios of 2, 3 and 5 are investigated. For AR=2 and 3, the wake structure shows an asymmetric helical shedding pattern. For AR=5, a regular patterns of quasi-axisymmetric rings are observed downstream of the torus shedding alternately in the streamwise direction. It is followed by a paper examining the Reynolds number effects on the vortical structure and the shedding pattern of the flow behind a torus with an aspect ratio of 3, utilizing IDDES, a hybrid RANS-LES method. Three Reynolds numbers of 150, 1500 and 15000 are studied and compared. For Re=150, the wake is laminar and exhibits a large-scale hairpin structure shedding alternately from the opposite side of the centerline axis. For Re=1500 and 15000, the wake stands in the turbulent regime. The vortical structure has a helical shedding pattern that disperses chaotically around the centerline axis. The striking difference between the Re=1500 and 15000 is the onset of the vortex roll-up, that occurs closer to the torus leeward surface for the Re=15000.

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