Large eddy simulations of two-phase flows around complex 3D geometries

Lopez, Santiago 2023. Large eddy simulations of two-phase flows around complex 3D geometries. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

This study presents the implementation of a new fluid-structure interaction model (FSI) in Hydro3D, a large eddy simulation (LES) code for computational fluid dynamics based on finite differences. A former model for studying fluid-structure interactions was a version of the Immersed Boundary Method (IBM) which has been validated for a wide range of Reynolds Numbers. However, it is challenging to ensure a sharp interface between the structure surface and the surounding fluid medium enforcing solid wall boundary conditions (no slip for velocity field and zero gradient for the pressure field) along the surface of an immersed body. Such initial IBM model implemented in Hydro3D diffuses this fluid-structure interface, introducing a source of error as a result. In order to cope with this, an enhanced model based on the ghost cell method (GCM) combining several interpolation techniques was tailored for Hydro3D. One of the innovative approaches is to combine the delta functions and hp shape function for interpolating field values for velocities and pressure, respectively. It was found that Hp scheme for interpolating the pressure field yields better results than the delta function when applying the ghost cell method to achieve a sharp interface. For interpolating velocities a delta function scheme was used. In the following chapters the reader can find a format description of the physical model, numerical validation results from CFD benchmarks for flows with fluid-structure interaction. The code also employs a level set method to simulate the motion of the free surface. In the LES simulations the Navier-Stokes equations (NSE) are spatially filtered and solved in a Cartesian grid employing a finite difference method. The time-advancing scheme for the flow fields is a version of the fractional step method with a Runge-Kutta method of three stages. The pressure Poisson equation (PPE) is solved by means of a multigrid TDMA technique. This software package is applied to simulate several benchmark cases in order to validate the numerical results,which for this research work comprise single-phase and two-phase flows. Next, the code is used to simulate two-phase flows of currents and waves over a vertical square, circular and elliptical cylinders and assess their deformation using a non-linear fine element solid solver. Finallly, a practical case study is presented to assess the performance and structural loads of a sea wall in the council of Tor-Bay.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Advanced Research Computing @ Cardiff (ARCCA) Engineering
Uncontrolled Keywords:	1).Fluid-Structure Interaction, aka FSI 2).Turbulence 3).Free-surface 4).Ghost-Cell Method 5).Finite Element Simulation 6).Coastal defense
Funders:	EPSRC
Date of First Compliant Deposit:	9 November 2023
Last Modified:	13 Jun 2024 16:06
URI:	https://orca.cardiff.ac.uk/id/eprint/163768

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