scholarly journals A Hybrid Parallel Numerical Model for Wave-Induced Free-Surface Flow

Fluids ◽  
2021 ◽  
Vol 6 (10) ◽  
pp. 350
Author(s):  
Georgios A. Leftheriotis ◽  
Iason A. Chalmoukis ◽  
Guillermo Oyarzun ◽  
Athanassios A. Dimas
Keyword(s):  
Free Surface ◽  
Numerical Model ◽  
Large Scale ◽  
Stokes Equations ◽  
Parallel Implementation ◽  
Three Dimensional ◽  
Free Surface Flow ◽  
Free Surface Flows ◽  
Surface Flow ◽  
Wave Induced

An advanced numerical model is presented for the simulation of wave-induced free-surface flow, utilizing an efficient hybrid parallel implementation. The model is based on the solution of the Navier–Stokes equations using large-eddy simulation of large-scale coastal free-surface flows. The three-dimensional immersed boundary method was used for the enforcement of the no-slip boundary condition on the bed surface. The water-air interface was tracked using the level-set method. The numerical model was effectively validated against laboratory measurements involving wave propagation over a flatbed with an elliptical shoal, whose presence induces combined wave refraction and diffraction phenomena. The parallel implementation of the model enabled the efficient simulation of depth-resolved, wave-induced, three-dimensional, free-surface flow; the model parallel efficiency and strong scaling are quantitatively demonstrated.

scholarly journals A Computational Fluid Dynamics Model for a Water Vortex Power Plant as Platform for Etho- and Ecohydraulic Research

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 639
Author(s):  
Dennis Powalla ◽  
Stefan Hoerner ◽  
Olivier Cleynen ◽  
Nadine Müller ◽  
Jürgen Stamm ◽  
...  
Keyword(s):  
Power Plant ◽  
Numerical Model ◽  
Large Scale ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Field Measurements ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Navier Stokes ◽  
Two Phase

The objective of the present paper is to develop a validated numerical model of a water vortex power plant that serves as a digital twin for further studies such as assessments of the ethohydraulic characteristics or the performance of such devices. The reference for the validation process is a large-scale hydraulic installation equipped with a full-scale water vortex power plant prototype installed in Dresden (Germany), where flow field measurements were carried out using three-dimensional Acoustic Doppler Velocimetry. The numerical model was implemented within the software package Star-CCM+. The unsteady, two-phase flow was solved with the Reynolds-Averaged Navier–Stokes equations in a Eulerian Multiphase approach, deploying a Volume of Fluid method to describe the free-surface flow. Water level and flow velocities were systematically compared in key areas of the device, demonstrating that the simulation is in good agreement with experimental observations. Relative differences are limited to at most 4% regarding water height in the system, and even the much more challenging velocity fields are reproduced with typical relative errors of roughly 10%. This validates the ability of the model to model the challenging flow conditions found in a water vortex power plant, enabling subsequent studies of the characteristics of this power plant concerning fish migration.

A Three Dimensional Non-Hydrostatic Numerical Model for Free Surface Flow and Mass Transportation

2013 ◽  
Vol 353-356 ◽  
pp. 2496-2501
Author(s):  
Biao Lv
Keyword(s):  
Numerical Model ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Navier Stokes ◽  
Mass Transportation ◽  
Governing Equations ◽  
Navier Stokes Equations ◽  
Good Agreement

A three dimensional non-hydrostatic numerical model is presented based on the incompressible Navier-Stokes equations and mass transport equations. An unstructured finite-volume technique is used to discretized the governing equations with good adaptable to complicated boundary. A conservative scalar transport algorithm is also applied in this model. An integral method of the top- layer pressure is applied to reduce the number of vertical layers. Three classical examples including periodic waves propagating over a submerged bar and non-hydrostatic lock exchange are used to demonstrate the capability and efficiency of the model. The simulation results are in good agreement with the analytical solution and experimental data.

Numerical Simulation of Free Surface Flows Using STACS-VOF Method

2007 ◽  
Author(s):  
Vedanth Srinivasan ◽  
De Ming Wang
Keyword(s):  
Free Surface ◽  
Stokes Equations ◽  
Current Method ◽  
Coupled System ◽  
Free Surface Flow ◽  
Surface Force ◽  
Free Surface Flows ◽  
Surface Flow ◽  
Air Entrapment ◽  
Simple Strategy

This paper presents a numerical method that couples the incompressible Navier-Stokes equations with the Volume of Fluid method in a Cartesian co-ordinate system for tracking immiscible interfaces in multiple dimensions. The governing equations are discretized based on a finite volume method on a non-staggered fixed grid. The free surface flow problem is solved as a single phase flow system in which the free surface is captured using a Switching Technique for Advection and Capturing of Surfaces (STACS) scheme. The effects of surface tension at the interfaces are treated using a Continuum Surface Force (CSF) model. The pressure velocity coupling is achieved using a SIMPLE strategy. The coupled system, implemented in the commercial CFD software, AVL FIRE/SWIFT, is applied to a two dimensional dam breaking problem. The simulation results reveal a multitude of phenomena such as, free surface vortex generation, air entrapment and splashing of the liquid surge front. The computational results are in good agreement with experimental data, wherever available. The effects of time and grid resolution on the solution behavior are elaborated in detail. Different convection schemes are tested and the current method is compared to another existing interface capturing methodology.

scholarly journals Numerical Study of Violent Impact Flow Using a CIP-Based Model

2013 ◽  
Vol 2013 ◽  
pp. 1-12 ◽  
Author(s):  
Qiao-ling Ji ◽  
Xi-zeng Zhao ◽  
Sheng Dong
Keyword(s):  
Free Surface ◽  
Numerical Model ◽  
Large Scale ◽  
Stokes Equations ◽  
Numerical Study ◽  
Three Dimensional ◽  
Small Scale ◽  
Surface Boundary ◽  
Two Phase ◽  
Constrained Interpolation

A two-phase flow model is developed to study violent impact flow problem. The model governed by the Navier-Stokes equations with free surface boundary conditions is solved by a Constrained Interpolation Profile (CIP)-based high-order finite difference method on a fixed Cartesian grid system. The free surface is immersed in the computation domain and expressed by a one-fluid density function. An accurate Volume of Fluid (VOF)-type scheme, the Tangent of Hyperbola for Interface Capturing (THINC), is combined for the free surface treatment. Results of another two free surface capturing methods, the original VOF and CIP, are also presented for comparison. The validity and utility of the numerical model are demonstrated by applying it to two dam-break problems: a small-scale two-dimensional (2D) and three-dimensional (3D) full scale simulations and a large-scale 2D simulation. Main attention is paid to the water elevations and impact pressure, and the numerical results show relatively good agreement with available experimental measurements. It is shown that the present numerical model can give a satisfactory prediction for violent impact flow.

Discharge Coefficient of Rectangular Side Weirs on Circular Channels

2016 ◽  
Vol 17 (7-8) ◽  
pp. 391-399 ◽  
Author(s):  
Hamed Azimi ◽  
Saeid Shabanlou ◽  
Isa Ebtehaj ◽  
Hossein Bonakdari
Keyword(s):  
Free Surface ◽  
Numerical Model ◽  
Flow Regime ◽  
Discharge Coefficient ◽  
Three Dimensional ◽  
Free Surface Flow ◽  
Energy Difference ◽  
Surface Flow ◽  
Side Weir ◽  
Supercritical Flow

AbstractIn this study, the flow turbulence and variations of the supercritical free surface flow in a circular channel along a side weir are simulated as three dimensional using the RNG k-ε turbulence model and volume of fluid (VOF) scheme. Comparison between the numerical model and experimental measurements shows that the numerical model simulates the free surface flow with good accuracy. According to the numerical model results, the specific energy variations along the side weir for the supercritical flow regime are almost constant and the energy drop is not significant but by increasing the side weir length the energy difference between the side weir upstream and downstream increases. Next, using the nonlinear regression (NLR) and analysis of the simulation results, some relationships for calculating the discharge coefficient of side weir on circular channels in supercritical flow regime are provided.

scholarly journals On ice-induced instability in free-surface flows

2007 ◽  
Vol 577 ◽  
pp. 25-52 ◽  
Author(s):  
EVGENIY SHAPIRO ◽  
SERGEI TIMOSHIN
Keyword(s):  
Free Surface ◽  
Three Dimensional ◽  
Water Film ◽  
Free Surface Flow ◽  
Free Surface Flows ◽  
Surface Flow ◽  
Two Dimensional ◽  
Instability Waves ◽  
Ice Surface ◽  
Neutral Curves

The problem of stability of a water-coated ice layer is investigated for a free-surface flow of a thin water film down an inclined plane. An asymptotic (double-deck) theory is developed for a flow with large Reynolds and Froude numbers which is then used to investigate linear two-dimensional, three-dimensional and nonlinear two-dimensional stability characteristics. A new mode of upstream-propagating instability arising from the interaction of the ice surface with the flow is discovered and its properties are investigated. In the linear limit, closed-form expressions for the dispersion relation and neutral curves are obtained for the case ofPr= 1. For the general case, the linear stability problem is solved numerically and the applicability of the solution withPr= 1 is analysed. Nonlinear double-deck equations are solved with a novel global-marching-type scheme and the effects of nonlinearity are investigated. An explanation of the physical mechanism leading to the upstream propagation of instability waves is provided.

A Stable Semi-Implicit Method for Free Surface Flows

2005 ◽  
Vol 73 (6) ◽  
pp. 940-947 ◽  
Author(s):  
Cassio M. Oishi ◽  
José A. Cuminato ◽  
Valdemir G. Ferreira ◽  
Murilo F. Tomé ◽  
Antonio Castelo ◽  
...  
Keyword(s):  
Free Surface ◽  
Boundary Conditions ◽  
Stokes Equations ◽  
Free Surface Flow ◽  
Free Surface Flows ◽  
Surface Flow ◽  
Navier Stokes ◽  
Variable Order ◽  
Implicit Methods ◽  
Time Lagged

The present work is concerned with a semi-implicit modification of the GENSMAC method for solving the two-dimensional time-dependent incompressible Navier-Stokes equations in primitive variables formulation with a free surface. A projection method is employed to uncouple the velocity components and pressure, thus allowing the solution of each variable separately (a segregated approach). The viscous terms are treated by the implicit backward method in time and a centered second order method in space, and the nonlinear convection terms are explicitly approximated by the high order upwind variable-order nonoscillatory scheme method in space. The boundary conditions at the free surface couple the otherwise segregated velocity and pressure fields. The present work proposes a method that allows the segregated solution of free surface flow problems to be computed by semi-implicit schemes that preserve the stability conditions of the related coupled semi-implicit scheme. The numerical method is applied to both the simulation of free surface and to confined flows. The numerical results demonstrate that the present technique eliminates the parabolic stability restriction required by the original explicit GENSMAC method, and also found in segregated semi-implicit methods with time-lagged boundary conditions. For low Reynolds number flows, the method is robust and very efficient when compared to the original GENSMAC method.

Coupled Dynamics of a Solid Piercing a Fluid Free Surface

2002 ◽  
Author(s):  
Remus M. Ciobotaru ◽  
Razvan Bidoae ◽  
Peter E. Raad
Keyword(s):  
Fluid Flow ◽  
Free Surface ◽  
Surface Deformation ◽  
Stokes Equations ◽  
Initial Conditions ◽  
Three Dimensional ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Second Phase ◽  
Submerged Sphere

This paper reports on numerical investigations of the dynamics of a moving sphere interacting with free surface flow in a three-dimensional, rectangular, confined channel. Each simulation consists of two phases. During the first phase, the sphere is fixed and the fluid flow around it is allowed to reach a stationary state. In the second phase, the sphere is allowed to oscillate vertically. The Froude number is shown to influence the dynamics of the sphere. Also, the influence of three different initial positions on the dynamics of the sphere are presented and discussed. The first initial condition corresponds to a surface-piercing sphere while the second and the third conditions correspond to a submerged sphere at two different depths beneath the free surface. The drag coefficient computed for the two initial conditions involving a fully submerged sphere is compared with the experimental (published) values for a sphere in an unbounded domain. The motion of the fluid flow around the moving solid body is based on the solution of the complete Navier-Stokes equations. The free surface deformation is solved by the use of an Eulerian-Lagrangian Marker and Micro Cell (ELMMC) method.

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