Date of Award

9-26-2018

Publication Type

Master Thesis

Degree Name

M.A.Sc.

Department

Mechanical, Automotive, and Materials Engineering

Keywords

Bluff body, Turbulence modeling, wake structure

Supervisor

Balachandar, Ram

Supervisor

Barron, Ronald

Rights

info:eu-repo/semantics/openAccess

Abstract

In this thesis, the effect of aspect ratio on the flow past square cross-section wall-mounted cylinders is evaluated using computational fluid dynamics. The simulations are carried out using the Improved Delayed Detached Eddy (IDDES) turbulence model. Three cases with different heights of the cylinder (aspect ratio = cylinder height/width = 1, 2, and 4) were studied. The IDDES prediction of the flow statistics is validated against a set of wind tunnel experimental results from a recent report on the flow at a Reynolds number of 12,000 for a cylinder aspect ratio of four. It is common practise to analyse results in different horizontal and vertical planes in the wake of the bluff body. To this end, the traditional methods use a geometrical scaling factor such as the height/diameter of the cylinder or depth of flow. However, this can lead to an improper analysis as one may not capture the flow properties based on the physics of the flow. The flow characteristics can be influenced by both the proximity to the bed and to the cylinder’s free-end. In this thesis, a new method, based on the flow physics, is proposed to evaluate the role of aspect ratio using the forebody pressure distribution. Using the turbulence features and vortex identification methods, it is observed that the flow structure is influenced by the aspect ratio. The downwash flow noticed in the wake tends to become less dominant with increasing aspect ratio, accompanied by a near-bed upwash flow at the rear of the cylinder. The mean and instantaneous flow field characteristics at each aspect ratio has been examined and compared in different planes to elucidate their three-dimensional features. The far-wake of each flow field is visualized and examined using the three-dimensional iso-surface of the λ2 criterion.

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