Reduced order modelling in nuclear reaction thermal hydraulics
Author(s)
Georgaka, Sokratia
Type
Thesis
Abstract
The context of the present thesis is to assess the potential of Reduced Order Models
(ROMs) for nuclear reactor thermal hydraulics applications. ROMs constitute advanced
modelling techniques aiming at fast high fidelity simulations. For the purposes of this research, two approaches have been selected and are investigated in depth: the Proper Orthogonal Decomposition (POD) with Galerkin projection (POD-Galerkin) and the hybrid method of Proper Orthogonal Decomposition with Interpolation using Radial Basis Functions, PODI - Galerkin, in the
context of parametric model order reduction. Additionally, in terms of the POD method, two sampling techniques are presented and compared: the standard and the nested POD.
The aforementioned methods are applied to a parametric case of non-isothermal mixing
in a T-junction pipe for laminar and turbulent
flow regimes. The flow is governed by the 3D, unsteady Navier - Stokes equations coupled with the energy equation.
Furthermore, a ROM for modelling buoyancy driven
flows with the Boussinesq approximation is discussed. Two cases are considered: a closed
flow, where the method is applied to a benchmark case of a differentially heated square cavity, and an open flow, where a case of a "cold-trap" formation in a U-bend pipe is investigated. The suitability of the above techniques is assessed based on a comparison between the reduced order results and those obtained using high fidelity OpenFOAM solvers.
(ROMs) for nuclear reactor thermal hydraulics applications. ROMs constitute advanced
modelling techniques aiming at fast high fidelity simulations. For the purposes of this research, two approaches have been selected and are investigated in depth: the Proper Orthogonal Decomposition (POD) with Galerkin projection (POD-Galerkin) and the hybrid method of Proper Orthogonal Decomposition with Interpolation using Radial Basis Functions, PODI - Galerkin, in the
context of parametric model order reduction. Additionally, in terms of the POD method, two sampling techniques are presented and compared: the standard and the nested POD.
The aforementioned methods are applied to a parametric case of non-isothermal mixing
in a T-junction pipe for laminar and turbulent
flow regimes. The flow is governed by the 3D, unsteady Navier - Stokes equations coupled with the energy equation.
Furthermore, a ROM for modelling buoyancy driven
flows with the Boussinesq approximation is discussed. Two cases are considered: a closed
flow, where the method is applied to a benchmark case of a differentially heated square cavity, and an open flow, where a case of a "cold-trap" formation in a U-bend pipe is investigated. The suitability of the above techniques is assessed based on a comparison between the reduced order results and those obtained using high fidelity OpenFOAM solvers.
Version
Open Access
Date Issued
2020-07
Date Awarded
2020-11
Copyright Statement
Creative Commons Attribution NonCommercial NoDerivatives Licence
Advisor
Bluck, Michael
Sponsor
Engineering and Physical Sciences Research Council ; ROLLS-ROYCE
Publisher Department
Mechanical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)