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Abstract
In this thesis, Large Eddy Simulation (LES) models are developed and used in conjunction with Computationl Fluid Dynamics (CFD) to simulate anisotropic turbulence inside and surrounding a CANDU fuel bundle structure. The CFD approach employs the Dynamic Smagorinsky Model (DSM), the SIMPLE coupling method, and a bounded central difference scheme to reduce numerical errors. The simulation results are used to predict (i) the dependence of turbulence intensity and the dominant frequency on the geometry and (ii) turbulence structures.
Results obtained from a full CFD model, including a whole simulation bundle and the upstream and downstream regions, indicate that the bundle geometric asymmetry and the upstream flow have significant effects on formation of axial vortices. The dynamic LES model has enabled a proper modeling of a transient vortical flow regime inside the bundle. Such flow induces oscillatory side forces and bundle vibrations (fretting).
An experimental apparatus was set up to measure the turbulent wall pressures in a pipe in the vicinity of the fuel bundle. The purpose of the pressure measurements is to provide a means for validating the simulation results. Good agreement was achieved between the simulation results and the experimental data for both mean and fluctuating wall pressures.
The validated computational approach is then used to develop a CFD model to simulate the heavy water flow through a fuel bundle under normal operating conditions (305°C at inlet) with heat transfer. At higher temperatures, the RMS values of the fluid forces and moment about the bundle centerline increase.
To address the solid-fluid interaction as result of the bundle rocking motion, a CFD model is developed to investigate the flow through the fuel bundle region for a prescribed sinusoidal motion using a dynamic mesh scheme.
The results reported in this thesis are new and of interest to the nuclear industry in identifying flow-induced vibration mechanisms concerning fretting and fretting-induced wear in CANDU fuel channels.
