Chiara Biscarini

CFD modelling approach for dam break flow studies

This paper presents numerical simulations of free surface flows induced by a dam break comparing the shallow water approach to fully three-dimensional simulations. The latter are based on the solution of the complete set of Reynolds-Averaged Navier-Stokes (RANS) equations coupled to the Volume of Fluid (VOF) method. The methods assessment and comparison are carried out on a dam break over a flat bed without friction, a dam break over a triangular bottom sill and a dam break flow over a 90 ◦ bend. Experimental and numerical literature data are compared to present results. The results demonstrate that the shallow water approach, even if able to sufficiently reproduce the main aspects of the fluid flows, loses some three-dimensional phenomena, due to the incorrect shallow water idealization that neglects the three-dimensional aspects related to the gravity force.

Hydrodynamics in Porous Media: A Finite Volume Lattice Boltzmann Study

Fluid flow through porous media is of great importance for many natural systems, such as transport of groundwater flow, pollution transport and mineral processing. In this paper, we propose and validate a novel finite volume formulation of the lattice Boltzmann method for porous flows, based on the Brinkman–Forchheimer equation. The porous media effect is incorporated as a force term in the lattice Boltzmann equation, which is numerically solved through a cell-centered finite volume scheme. Correction factors are introduced to improve the numerical stability. The method is tested against fully porous Poiseuille, Couette and lid-driven cavity flows. Upon comparing the results with well-documented data available in literature, a satisfactory agreement is observed. The method is then applied to simulate the flow in partially porous channels, in order to verify its potential application to fractured porous conduits, and assess the influence of the main porous media parameters, such as Darcy number, porosity and porous media thickness.

Detailed Simulation of Complex Hydraulic Problems with Macroscopic and Mesoscopic Mathematical Methods

The numerical simulation of fast-moving fronts originating from dam or levee breaches is a challenging task for small scale engineering projects. In this work, the use of fully three-dimensional Navier-Stokes (NS) equations and lattice Boltzmann method (LBM) is proposed for testing the validity of, respectively, macroscopic and mesoscopic mathematical models. Macroscopic simulations are performed employing an open-source computational fluid dynamics (CFD) code that solves the NS combined with the volume of fluid (VOF) multiphase method to represent free-surface flows. The mesoscopic model is a front-tracking experimental variant of the LBM. In the proposed LBM the air-gas interface is represented as a surface with zero thickness that handles the passage of the density field from the light to the dense phase and vice versa. A single set of LBM equations represents the liquid phase, while the free surface is characterized by an additional variable, the liquid volume fraction. Case studies show advantages and disadvantages of the proposed LBM and NS with specific regard to the computational efficiency and accuracy in dealing with the simulation of flows through complex geometries. In particular, the validation of the model application is developed by simulating the flow propagating through a synthetic urban setting and comparing results with analytical and experimental laboratory measurements.

Application of the lattice Boltzmann method for large‐scale hydraulic problems

Purpose – The purpose of this paper is to prove the validity of the front‐tracking variant of the lattice Boltzmann method (LBM) to simulate free surface hydraulic flows (i.e. dam break flows).Design/methodology/approach – In this paper, an algorithm for free surface simulations with the LBM method is presented. The method is chosen for its computational efficiency and ability to deal with complex geometries. The LBM is combined to a surface‐tracking technique applied to a fixed Eulerian mesh in order to simulate free surface flows.Findings – The numerical method is then validated against two typical cases of environmental‐hydraulic interest (i.e. dam break) by comparing LBM results with experimental data available in literature. The results show that the model is able to reproduce the observed water levels and the wave fronts with reasonable accuracy in the whole period of the transient simulations, thus highlighting that the present method may be a promising tool for practical dam break analyses.Origina...

POROUS SUBSTRATE EFFECTS ON THERMAL FLOWS THROUGH A REV-SCALE FINITE VOLUME LATTICE BOLTZMANN MODEL

In this paper, fluid flows with enhanced heat transfer in porous channels are investigated through a stable finite volume (FV) formulation of the thermal lattice Boltzmann method (LBM). Temperature field is tracked through a double distribution function (DDF) model, while the porous media is modeled using Brinkman–Forchheimer assumptions. The method is tested against flows in channels partially filled with porous media and parametric studies are conducted to evaluate the effects of various parameters, highlighting their influence on the thermo-hydrodynamic behavior.

On the impact of urbanization on flood hydrology of small ungauged basins: the case study of the Tiber river tributary network within the city of Rome

The small ungauged basins of the highly urbanized area of the city of Rome are often the subject of critical flood conditions for the significant human-made transformations. In this work the EBA4SUB framework, implementing the hydrogeomorphic width function instantaneous unit hydrograph rainfall run-off model, and using digital elevation model, land use and synthetic precipitation as main input information, is applied for evaluating extreme hydrologic forcing conditions at the basic scale. The goal is to understand the rationale behind the observed increasing frequency of local urban inundations that are also observed in the uplands. Results present the impact of urbanization expressed by both the run-off coefficient, the artificial drainage, impacted by paved surfaces and a dramatic number of river–road intersections (i.e. culverts), and the upstream to downstream non-natural scaling behaviour of hydrologic parameters and in particular the peak discharge per unit drainage area.

Wall roughness effect in the lattice Boltzmann method

Lattice Boltzmann Method (LBM) is reported for free surface flow in rough-wall plane duct flow. For this purpose, the partial-slip boundary condition is considered to account for the wall roughness. The pressure pipe flow is selected as a benchmark to validate the method. The effect of partial-slip coefficient on the hydraulic loss and pressure drop at different Reynolds numbers is investigated and discussed.

Three-dimensional numerical modelling of the Marmore waterfalls

This paper describes the application of a three-dimensional Computational Fluid Dynamic (CFD) model to simulate the Marmore waterfall (Italy), which is part of the complex hydraulic system Nera Velino rivers, Piediluco lake. The domain reconstruction has been performed through a non-conventional photogrammetry topographic surveying. The simulations have been performed employing a CFD model that solves the Navier-Stokes equations with the Large Eddy Simulations turbulence closure scheme and the Volume of Fluid multiphase method to handle the free-surface flow. A good agreement is achieved between the CFD model and the real waterfall flow.

Dynamic monitoring of compliant bodies impacting the water surface through local strain measurements

The understanding and the experimental characterization of the evolution of impulsive loading is crucial in several fields in structural, mechanical and ocean engineering, naval architecture and aerospace. In this regards, we developed an experimental methodology to reconstruct the deformed shape of compliant bodies subjected to impulsive loadings, as those encountered in water entry events, starting from a finite number of local strain measurements performed through Fiber Bragg Gratings. The paper discusses the potential applications of the proposed methodology for: i) real-time damage detection and structural health monitoring, ii) fatigue assessment and iii) impulsive load estimation.

LBM method for roughness effect in open channel flows

In this workwe present an enhancement of a free-surface Lattice Boltzmannmethod to evaluate pressure losses and wall roughness effects. Recent works in literature propose strategies to account for wall roughness, but mainly in small-scale computational domains, [1,2] or by means of a 2D approach, [3]. In the frame of 2D analyses, friction term has been defined in the shallow water problem as a function of slope of the bottom of the domain, roughness and water depth, [4]. In this work, three different strategies are proposed to account for wall roughness: a Smagorinsky-based approach, with an ad-hoc function to vary turbulent viscosity with the distance from the wall, an implementation of a partial-slip wall boundary collision and the simulation of roughness effects by means of an external force field, accounted for in the collision phase.