A closure-independent Generalized Roe solver for free-surface, two-phase flows over mobile bed

2013 ◽  
Vol 255 ◽  
pp. 362-383 ◽  
Author(s):  
Giorgio Rosatti ◽  
Lorenzo Begnudelli
Keyword(s):  
Free Surface ◽  
Two Phase Flows ◽  
Two Phase ◽  
Mobile Bed ◽  
Roe Solver

scholarly journals A Discrete-Forcing Immersed Boundary Method for Moving Bodies in Air–Water Two-Phase Flows

2020 ◽  
Vol 8 (10) ◽  
pp. 809
Author(s):  
Haixuan Ye ◽  
Yang Chen ◽  
Kevin Maki
Keyword(s):  
Free Surface ◽  
Immersed Boundary Method ◽  
Surface Profile ◽  
Field Extension ◽  
Immersed Boundary ◽  
Two Phase Flows ◽  
Two Phase ◽  
Practical Applications ◽  
Boundary Method ◽  
Immersed Boundaries

For numerical simulations of ship and offshore hydrodynamic problems, it is challenging to model the interaction between the free surface and moving complex geometries. This paper proposes a discrete-forcing immersed boundary method (IBM) to efficiently simulate moving solid boundaries in incompressible air–water two-phase flows. In the present work, the air–water two-phase flows are modeled using the Volume-of-Fluid (VoF) method. The present IBM is suitable for unstructured meshes. It can be used combined with body-fitted wall boundaries to model the relative motions between solid walls, which makes it flexible to use in practical applications. A field extension method is used to model the interaction between the air–water interface and the immersed boundaries. The accuracy of the method is demonstrated through validation cases, including the three-dimensional dam-break problem with an obstacle, the water exit of a circular cylinder, and a ship model advancing with a rotating semi-balanced rudder. The flow field, free-surface profile and force on the immersed boundaries (IBs) are in good agreement with experimental data and other numerical results.

Modelling of Free Surface Flow Within the Two-Fluid Euler-Euler Framework

2015 ◽  
Author(s):  
Paul Porombka
Keyword(s):  
Free Surface ◽  
Large Scale ◽  
Flow Regimes ◽  
Free Surface Flows ◽  
Two Phase Flows ◽  
Two Phase ◽  
Surface Flows ◽  
Macro Scale ◽  
Interfacial Drag ◽  
Two Fluid

Two-phase flows are regularly involved in the heat and mass transfer of industrial processes. To ensure the safety and efficiency of such processes, accurate predictions of the flow field and phase distribution by means of Computational Fluid Dynamics (CFD) are required. Direct Numerical Simulations (DNS) of large-scale two-phase flow problems are not feasible due to the computational costs involved. Therefore the Euler-Euler framework is often employed for large-scale simulations which involves macro-scale modelling of the turbulent shear stress and the interphase momentum transfer. As a long term objective, the research activities at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) pursue the development of general models for two-phase flows which are based on first principles and include less empiricism. Part of this effort is focused on the development of an algebraic interfacial area density model (AIAD) which enables the simulation of two-phase flows with general morphologies including bubble, droplet and stratified flow regimes with the two-fluid approach. In this work a short overview of the AIAD model is given and recent developments are presented. The modelling of the interfacial drag in free surface flows is of particular interest and subject to ongoing research. Apart from empirical correlations, which are limited to certain flow regimes, different models for the local calculation of the interfacial drag have been developed. The latter approach is followed in the AIAD model and has recently been subject to modifications which are presented and validated as a part of this study. Furthermore, special attention is paid to the turbulence treatment at the phase boundary of free surface flows. A general damping of the gas-side turbulent fluctuations in the near interface region has been described previously in the literature but has not yet found its way into eddy viscosity turbulence models. In this work, a previously proposed damping source term for the k-ω turbulence model is validated. Model validation is performed by comparing the simulation results to experimental data in case of stratified, countercurrent air-water flow in a closed channel.

Generalized Roe schemes for 1D two-phase, free-surface flows over a mobile bed

2008 ◽  
Vol 227 (24) ◽  
pp. 10058-10077 ◽  
Author(s):  
G. Rosatti ◽  
J. Murillo ◽  
L. Fraccarollo
Keyword(s):  
Free Surface ◽  
Free Surface Flows ◽  
Two Phase ◽  
Surface Flows ◽  
Mobile Bed

scholarly journals Cahn-Hilliard Navier-Stokes simulations for marine free-surface flows

2021 ◽  
Author(s):  
Niklas Kühl ◽  
Michael Hinze ◽  
Thomas Rung
Keyword(s):  
Surface Tension ◽  
Free Surface ◽  
Bubble Formation ◽  
Free Surface Flows ◽  
Navier Stokes ◽  
Steady Flows ◽  
Two Phase Flows ◽  
Time Step ◽  
Two Phase ◽  
Surface Flows

AbstractThe paper is devoted to the simulation of maritime two-phase flows of air and water. Emphasis is put on an extension of the classical Volume-of-Fluid (VoF) method by a diffusive contribution derived from a Cahn-Hilliard (CH) model and its benefits for simulating immiscible, incompressible two-phase flows. Such flows are predominantly simulated with implicit VoF schemes, which mostly employ heuristic downwind-biased approximations for the concentration transport to mimic a sharp interface. This strategy introduces a severe time step restriction and requires pseudo time-stepping of steady flows. Our overall goal is a sound description of the free-surface region that alleviates artificial time-step restrictions, supports an efficient and robust upwind-based approximation framework, and inherently includes surface tension effects when needed. The Cahn-Hilliard Navier-Stokes (CH-NS) system is verified for an analytical Couette-flow example and the bubble formation under the influence of surface tension forces. 2D validation examples are concerned with laminar standing waves reaching from gravity to capillary scale as well as a submerged hydrofoil flow. The final application refers to the 3D flow around an experimentally investigated container vessel at fixed floatation for Re = 1.4 × 107 and Fn = 0.26. Results are compared with data obtained from VoF approaches, supplemented by analytical solutions and measurements. The study indicates the superior efficiency, resharpening capability, and wider predictive realm of the CH-based extension for free-surface flows with a confined spatial range of interface Courant numbers.

scholarly journals Validation of AIAD Sub-Models for Advanced Numerical Modelling of Horizontal Two-Phase Flows

Fluids ◽  
2020 ◽  
Vol 5 (3) ◽  
pp. 102 ◽  
Author(s):  
Thomas Höhne ◽  
Paul Porombka ◽  
Senen Moya Sáez
Keyword(s):  
Free Surface ◽  
Turbulence Models ◽  
Free Surface Flows ◽  
Mean Flow ◽  
Surface Drag ◽  
Two Phase Flows ◽  
Two Phase ◽  
Detection Mechanism ◽  
Surface Flows ◽  
Blending Functions

In this work, the modelling of horizontal two-phase flows within the two-fluid Euler–Euler approach is investigated. A modified formulation of the morphology detection functions within the Algebraic Interfacial Area Density (AIAD) model is presented in combination with different models for the drag force acting on a sheared gas–liquid interface. In the case of free surface flows, those closure laws are often based on experimental correlations whose applicability is limited to certain flow regimes. It is investigated here whether the implementation of the modified blending functions in ANSYS CFX avoids this limitation. The influence of the new functions on the prediction of turbulence parameters in free surface flows is also examined quantitatively for the k-ω and k-ε two-equation turbulence models. Transient simulations of the WENKA counter-current stratified two-phase flow experiment were performed for validation. A prediction of the correct flow pattern as observed in the experiment improved dramatically when a turbulence damping term was included in the standard two-equation models. Using the k-ω and a modified k-ε turbulence model with damping terms close to the interface, better agreement with the experimental data was achieved. The morphology detection mechanism of the unified blending functions within the AIAD is seen as an improvement with respect to the detection of sharp interfaces. Satisfactory quantitative agreement is achieved for the modified free surface drag. Furthermore, it is demonstrated that turbulence dampening has to be accounted for in both turbulence models to qualitatively reproduce the mean flow and turbulence quantities from the experiment.

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