Modelling of Flow in Vertical Porous Structures Solving the Reynolds-Averaged Navier-Stokes Equations (RANS) using the Volume of Fluid Method (VOF)

Diploma Thesis from the year 2001 in the subject Engineering - Civil Engineering, grade: 2,0, Technical University of Braunschweig (Bauingenieurwesen), language: English, abstract: Inhaltsangabe:Abstract:§In this thesis the simulation of the flow in alpha vertical permeable structure with alpha free surface is described. The underlying physical data had been achieved from experiments in a wave flume at the University of Cantabria. For the calibration of the numerical model COBRAS, a VOF type programme developed at Cornell University, the numerical results are compared with the laboratory data. The data analysed comes from 8 free surface sensors, placed inside and outside of the porous structure, and 4 pressure sensors, placed on the impermeable back wall inside the porous structure. An error analysis, using the least square technique, lead to a stepwise improvement of the numerical and the porous media parameters. In this process various grids had been tested, concerning sponge layer length, source function position and cell size. Later the porous media parameter for laminar and turbulent flow had been adjusted. For various wave conditions and porous structure characteristics, the optimal values for these parameters turned out to lay between 0 and 200 for alpha and between 0.45 and 0.8 for beta. The following error analysis yielded to alpha=100 and beta=0.5 usable for all tested wave and porous media characteristics.§Inhaltsverzeichnis:Table of Contents:§1.Introduction1§1.1General Introduction1§1.2Aims of study3§1.3Contents3§2.Numerical Modelling5§2.1Introduction5§2.2Overview of Numerical Models for Wave prediction6§2.3Numerical Models for Simulation of Flow in porous media7§2.3.1Overview of mathematical solutions7§2.3.2Available numerical models for porous media flow8§2.4The COBRAS Model9§2.4.1Overview9§2.4.2Governing Equations for the Mean Flow9§2.4.2.1Flow Motion Formulation9§2.4.2.1.1Navier-Stokes Equations and Boundary Conditions9§2.4.2.1.2Reynolds Equations and Boundary Conditions12§2.4.2.2Turbulence Transport Model14§2.4.2.2.1Transport Equation for Turbulent Kinetic Energy, k14§2.4.2.2.2The Transport Equation for Turbulent Dissipation Rate, F15§2.4.2.2.3Assumptions and Determinations of Coefficients in the k-s Model 16§2.4.2.2.4Boundary Conditions for k and s19§2.4.2.3Summary of Governing Equations19§2.4.3Modelling of Flow in Porous Media20§2.4.4The Volume of Fluid Method25§2.4.5The Source Function27§2.4.6The Sponge Layer28§2.4.7Numerical Algorithm30§2.5Closing comment31§3.Vertical Permeable Structures32§3.1Introduction32§3.2Motivation of the Experiments34§3.3Overview of the experiments34§3.4Closing comment37§4.Simulation of Flow in Vertical Permeable Structures38§4.1Introduction38§4.2Determination of the Mesh Parameters39§4.2.1Overview39§4.2.2Source Function Position and Length of Wave Stabilization Zone41§4.2.3Length of Sponge Layer50§4.2.4Size of computational Cells56§4.2.5Overview of chosen Grid Parameters59§4.3Determination of Porous Media Parameters 60§4.3.1Overview60§4.3.2Sensitivity of a and60§4.3.3Variation of the wave height64§4.3.4Variation of the wave period67§4.3.5Variation of the gabion width70§4.3.6Variation of the stone diameter73§4.4Closing comment75§5.Conclusions and Recommendations78§5.1Conclusions78§5.1.1Discussion of the influences to the porous media parameters and78§5.1.2General conclusions80§5.2Recommendations81