Date of Award

7-7-2020

Publication Type

Master Thesis

Degree Name

M.A.Sc.

Department

Mechanical, Automotive, and Materials Engineering

Keywords

Dean vortices, Fully developed turbulent flow, Reynolds Stress turbulence model, Square duct, Two-pass channel with a 180° turn

Supervisor

Ram Balachandar

Supervisor

Vesselina Roussinova

Rights

info:eu-repo/semantics/openAccess

Abstract

Two-pass flow channels with a square or rectangular cross-section are used in many thermo-fluid systems such as air-conditioners, heat exchangers, cooling passages of gas turbine blades, etc. As the flow passes through these channels, it becomes highly three-dimensional. This complexity is due to the Dean-type secondary motion, flow separation and impingement in the turn. Our approach is to first investigate the turbulent flow in a pressure-driven straight square duct at a high Reynolds number (Re = 40,000) to reach flow conditions which are representative of fully developed turbulence. Numerical simulations are carried out to investigate the nature of the secondary flow in a square duct through velocity and vorticity fields. The results are validated with the DNS study of Pirozzoli et al. (2018). Following this validation, another square duct simulation at a higher Reynolds number (Re = 50,000) is carried out as the numerical strategy for the two-pass channel requires a fully developed turbulence inlet condition. This is used as the approach flow condition at the inlet of the two-pass channel. The results of this two-pass channel simulation (Re = 50,000) before the turn, in the turn and after the turn are validated by comparing it with the PIV data of Schabacker et al., (1998b). The influence of the bend clearance on the turbulence parameters of the flow, the three-dimensionality of the flow and the complexity of Dean-type secondary motion, flow separation and flow recirculation is examined. The turbulence structures within the flow are identified using a vortex identification criterion, namely Q-criterion. These structures reveal the complexity of turbulence in the flow field of two-pass channel, mainly the recirculation region. The comparison of Q-criterion with two different bend clearances is carried out to study the influence of the bend clearance on the turbulent structures formed in the two-pass channel.

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