Date of Award

10-5-2017

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Mechanical, Automotive, and Materials Engineering

First Advisor

Barron, Ronald

Second Advisor

Balachandar, Ram

Keywords

Bluff body, Computational Fluid Dynamics, Solar panel, Three-dimensional flow instability, Turbulence, Vortex

Abstract

This thesis uses numerical investigations to examine details of the turbulent flow past bluff bodies, in particular around various inclined flat plate configurations. The study consists of three phases: (1) flow past an infinitely long inclined flat plate, (2) flow past a finite length inclined flat plate near a wall and (3) flow past a stand-alone solar panel with support structure. In Phase 1, the development of three-dimensional fluid structures around an infinitely long inclined flat plate at Reynolds number of 1.57×105 is reported. The Detached Eddy Simulation (DES) is validated against well-established experimental data. The flow analysis in two-dimensional planes provides fundamental information about the spanwise and streamwise vortices that develop near the body and in its wake, but offers limited information on the formation and evolution of these vortices. Using the λ2-criterion to visualize the three-dimensional fluid structures, the interaction between the spanwise and streamwise vortical structures and the shear layers is discussed. It is found that the spanwise wavelength of the streamwise vortical structures lie in the range corresponding to the mode B instability reported in previous studies of wake transition. The effect of a wall on the flow structures around a finite length inclined flat plate at two proximities from the wall is investigated in Phase 2. In the mean analysis, it is found that the small clearance produces a wall-jet like flow in the gap which elongates the wake region, whereas a strong upwash is captured for the larger gap, reducing the length of the wake. Transient three-dimensional flow structures are captured using the λ2-criterion. The early stage development of the flow around the plate shows inverted hairpin-like vortices that generate a counter-rotating sheared vortex and a pair of vertical vortex tubes extending from the wall. This pair of vortex tubes is considered as the source of the meandering structures reported in the literature. At the later flow development stage, an asymmetric distorted flow for the smaller gap is observed, whereas there is a nearly symmetric wake pattern for the larger gap. Numerical investigation of flow past a stand-alone solar panel with a supporting post is conducted using DES in Phase 3. Two elevations of the solar panel are examined. Mean velocity profiles and two-dimensional mean vorticity contours do not illustrate significant changes in the flow patterns, except for relatively weak vortices that develop along the post. The transient three-dimensional analysis using the λ2-criterion captures four unique fluid structures around the body for the small gap case. On the other hand, the large gap case shows minimum influence from the post except for ligaments of vortex tubes that extend from the post. The same vortex structures also develop in the small gap case but are merged into the large scale vortices in the wake.

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