The effects of surface roughness on the flow in multiple connected fractures

2022 ◽  
Author(s):  
Pouria Aghajannezhad ◽  
Mathieu Sellier
Keyword(s):  
Surface Roughness ◽  
Hydraulic Resistance ◽  
Flow Rate ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Roughness Coefficient ◽  
Computationally Efficient ◽  
Navier Stokes Equations ◽  
Discrete Fracture Networks ◽  
The Impact

Abstract We present a novel computationally efficient approach for investigating the effect of surface roughness on the fluid flow in discrete fracture networks at low Reynolds number. The effect of parallel and series fracture arrangements on the flow rate and hydraulic resistance was studied numerically by patching Hele-Shaw (HS) cells to represent the network. In this analysis, the impact of surface roughness was studied in different arrangements of the network. For this aim, four models with different sequences of fracture connections were studied. The validity of the models was assessed by comparing the results with solutions of the full Navier-Stokes equations (NSE). The approximate hydraulic resistance and flow rate calculated by the HS method were found to be in good agreement with the NSE (less than 7% deviation). Results suggest a quadratic relationship between the network hydraulic resistance and the joint roughness coefficient (JRC). Notably, an increase in surface roughness caused a growth in hydraulic resistance and a fall in flow rate. Further insight was provided by drawing an analogy between resistors in electrical circuits and fractures in networks.

scholarly journals Fluid-kinetic modelling for respiratory aerosols with variable size and temperature

2020 ◽  
Vol 67 ◽  
pp. 100-119 ◽  
Author(s):  
Laurent Boudin ◽  
Céline Grandmont ◽  
Bérénice Grec ◽  
Sébastien Martin ◽  
Amina Mecherbet ◽  
...  
Keyword(s):  
Stokes Equations ◽  
Kinetic Modelling ◽  
Type Equation ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Aerosol Dynamics ◽  
Convection Diffusion Equation ◽  
Time Marching ◽  
Branched Structure ◽  
The Impact

In this paper, we propose a coupled fluid-kinetic model taking into account the radius growth of aerosol particles due to humidity in the respiratory system. We aim to numerically investigate the impact of hygroscopic effects on the particle behaviour. The air flow is described by the incompressible Navier-Stokes equations, and the aerosol by a Vlasov-type equation involving the air humidity and temperature, both quantities satisfying a convection-diffusion equation with a source term. Conservations properties are checked and an explicit time-marching scheme is proposed. Twodimensional numerical simulations in a branched structure show the influence of the particle size variations on the aerosol dynamics.

scholarly journals Flow Pressure Behavior Downstream of Ski Jumps

Fluids ◽  
2020 ◽  
Vol 5 (4) ◽  
pp. 168 ◽  
Author(s):  
Agostino Lauria ◽  
Giancarlo Alfonsi ◽  
Ali Tafarojnoruz
Keyword(s):  
High Speed ◽  
Stokes Equations ◽  
Dynamic Pressure ◽  
Pressure Head ◽  
Navier Stokes ◽  
Maximum Pressure ◽  
Navier Stokes Equations ◽  
Free Jet ◽  
Jet Characteristics ◽  
The Impact

Ski jump spillways are frequently implemented to dissipate energy from high-speed flows. The general feature of this structure is to transform the spillway flow into a free jet up to a location where the impact of the jet creates a plunge pool, representing an area for potential erosion phenomena. In the present investigation, several tests with different ski jump bucket angles are executed numerically by means of the OpenFOAM® digital library, taking advantage of the Reynolds-averaged Navier–Stokes equations (RANS) approach. The results are compared to those obtained experimentally by other authors as related to the jet length and shape, obtaining physical insights into the jet characteristics. Particular attention is given to the maximum pressure head at the tailwater. Simple equations are proposed to predict the maximum dynamic pressure head acting on the tailwater, as dependent upon the Froude number, and the maximum pressure head on the bucket. Results of this study provide useful suggestions for the design of ski jump spillways in dam construction.

scholarly journals Development of An Integrated Numerical Model for Simulating Wave Interaction with Permeable Submerged Breakwaters Using Extended Navier–Stokes Equations

2020 ◽  
Vol 8 (2) ◽  
pp. 87 ◽  
Author(s):  
Paran Pourteimouri ◽  
Kourosh Hejazi
Keyword(s):  
Porous Medium ◽  
Wave Propagation ◽  
Numerical Model ◽  
Analytical Solutions ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Stokes Wave ◽  
Navier Stokes Equations ◽  
Numerical Predictions ◽  
The Impact

An integrated two-dimensional vertical (2DV) model was developed to investigate wave interactions with permeable submerged breakwaters. The integrated model is capable of predicting the flow field in both surface water and porous media on the basis of the extended volume-averaged Reynolds-averaged Navier–Stokes equations (VARANS). The impact of porous medium was considered by the inclusion of the additional terms of drag and inertia forces into conventional Navier–Stokes equations. Finite volume method (FVM) in an arbitrary Lagrangian–Eulerian (ALE) formulation was adopted for discretization of the governing equations. Projection method was utilized to solve the unsteady incompressible extended Navier–Stokes equations. The time-dependent volume and surface porosities were calculated at each time step using the fraction of a grid open to water and the total porosity of porous medium. The numerical model was first verified against analytical solutions of small amplitude progressive Stokes wave and solitary wave propagation in the absence of a bottom-mounted barrier. Comparisons showed pleasing agreements between the numerical predictions and analytical solutions. The model was then further validated by comparing the numerical model results with the experimental measurements of wave propagation over a permeable submerged breakwater reported in the literature. Good agreements were obtained for the free surface elevations at various spatial and temporal scales, velocity fields around and inside the obstacle, as well as the velocity profiles.

scholarly journals Two-Dimensional Modelling of a Quayside Floating System

2020 ◽  
Vol 8 (11) ◽  
pp. 903
Author(s):  
Sixtine Neuvéglise ◽  
Gaële Perret ◽  
Hassan Smaoui ◽  
François Marin ◽  
Philippe Sergent
Keyword(s):  
Stokes Equations ◽  
Numerical Models ◽  
Navier Stokes ◽  
Intermediate Water ◽  
Navier Stokes Equations ◽  
Quadratic Drag ◽  
Floating System ◽  
Physical Tests ◽  
Comparison Of The Results ◽  
The Impact

This paper studies the behaviour of a quayside floater oscillating in front of a vertical dike. In order to study the floater motion and the impact of the dike on the floater, a linear analytical model based on 2D potential flow theory in intermediate water depth conditions and a numerical model resolving 2D Navier–Stokes equations are developed. Physical tests performed for different floater dimensions in a wave tank are used as references for the analytical and numerical models. The comparison of the results obtained analytically, numerically and experimentally leads to the validity domain of the potential model. A correction of this model is proposed, based on the optimization of the radiated coefficients, and a quadratic drag term is added according to Morison equation. The impact of the different parameters of the system on floater behaviour is considered. Results show that the draft has the most important impact on floater motion.

The Effect of Blade Lean, Twist and Bow on the Performance of Axial Turbine at Design Point

2011 ◽  
Author(s):  
Hadi Karrabi ◽  
Mohsen Rezasoltani
Keyword(s):  
Stokes Equations ◽  
Numerical Data ◽  
Navier Stokes ◽  
Minor Effect ◽  
Complex Flow ◽  
Navier Stokes Equations ◽  
Axial Turbine ◽  
Twisted Blade ◽  
The Impact ◽  
Good Agreement

An investigation to understand the impact of twisted, leaned and bowed blades on the performance of axial turbine was undertaken. A CFD code, which solves the Reynolds-averaged Navier–Stokes equations, was used to compute the complex flow field of axial turbine. The code was validated against existing Hannover turbine experimental data. Numerical data showed good agreement with measured data. Finally, the effect of geometry changes, focusing on blade lean, twist and bow, on the Avon turbine blade performance, was analyzed. Results show that twisted blade affects performance significantly. Leaned and bowed blade has minor effect on performance.

scholarly journals A Computational Study of a Data Assimilation Algorithm for the Two-dimensional Navier-Stokes Equations

2016 ◽  
Vol 19 (4) ◽  
pp. 1094-1110 ◽  
Author(s):  
Masakazu Gesho ◽  
Eric Olson ◽  
Edriss S. Titi
Keyword(s):  
Data Assimilation ◽  
Stokes Equations ◽  
Computational Study ◽  
Nodal Point ◽  
Navier Stokes ◽  
Reference Solution ◽  
Two Dimensional ◽  
Computationally Efficient ◽  
Navier Stokes Equations ◽  
Feedback Control Theory

AbstractWe study the numerical performance of a continuous data assimilation (downscaling) algorithm, based on ideas from feedback control theory, in the context of the two-dimensional incompressible Navier-Stokes equations. Our model problem is to recover an unknown reference solution, asymptotically in time, by using continuous-in-time coarse-mesh nodal-point observational measurements of the velocity field of this reference solution (subsampling), as might be measured by an array of weather vane anemometers. Our calculations show that the required nodal observation density is remarkably less than what is suggested by the analytical study; and is in fact comparable to the number of numerically determining Fourier modes, which was reported in an earlier computational study by the authors. Thus, this method is computationally efficient and performs far better than the analytical estimates suggest.

Oscillatory forcing of flow through porous media. Part 1. Steady flow

2002 ◽  
Vol 465 ◽  
pp. 213-235 ◽  
Author(s):  
D. R. GRAHAM ◽  
J. J. L. HIGDON
Keyword(s):  
Porous Media ◽  
Flow Rate ◽  
Stokes Equations ◽  
Nonlinear Flow ◽  
Navier Stokes ◽  
Full Time ◽  
Inertial Effects ◽  
Mean Flow ◽  
Navier Stokes Equations ◽  
The Mean

Oscillatory forcing of a porous medium may have a dramatic effect on the mean flow rate produced by a steady applied pressure gradient. The oscillatory forcing may excite nonlinear inertial effects leading to either enhancement or retardation of the mean flow. Here, in Part 1, we consider the effects of non-zero inertial forces on steady flows in porous media, and investigate the changes in the flow character arising from changes in both the strength of the inertial terms and the geometry of the medium. The steady-state Navier–Stokes equations are solved via a Galerkin finite element method to determine the velocity fields for simple two-dimensional models of porous media. Two geometric models are considered based on constricted channels and periodic arrays of circular cylinders. For both geometries, we observe solution multiplicity yielding both symmetric and asymmetric flow patterns. For the cylinder arrays, we demonstrate that inertial effects lead to anisotropy in the effective permeability, with the direction of minimum resistance dependent on the solid volume fraction. We identify nonlinear flow phenomena which might be exploited by oscillatory forcing to yield a net increase in the mean flow rate. In Part 2, we take up the subject of unsteady flows governed by the full time-dependent Navier–Stokes equations.

Heat Transfer Generated by the Interaction of Single and Multiple Tandem Jets in Crossflow

2010 ◽  
Author(s):  
Amina Radhouane ◽  
Nejla Mahjoub ◽  
Hatem Mhiri ◽  
George Lepalec ◽  
Philippe Bournot
Keyword(s):  
Heat Transfer ◽  
Stokes Equations ◽  
Reynolds Stress Model ◽  
Navier Stokes ◽  
Uniform Grid ◽  
Cooling Power ◽  
Small Scale ◽  
Fluid Composition ◽  
Navier Stokes Equations ◽  
The Impact

“Twin jets in Crossflow” is a common configuration that finds application in several large and/or small scale industrial fields. The interest in such a configuration is further enhanced by its dependence in several parameters, that may be geometric, dynamic, thermal, or relative to the handled fluid composition. We propose to focus in the present work on the effect of the number of the emitted jets on the generated heat transfer, in presence of an unchanged uniform crossflow. To reach this goal, single, double and triple jet configurations were simulated, based upon the resolution of the Navier Stokes equations by means of the RSM (Reynolds Stress Model) second order turbulent closure model, together with a non uniform grid system particularly tightened near the emitting nozzles. After validation, we tried to find out the impact of the number of the handled jets on their cooling “power” by tracking the temperature distribution of the resulting flowfield. Since in practically all applications we are in need of higher efficiencies and then of higher operating temperatures, we are constantly concerned about not going beyond the shielding material melting temperature. If the use of cooling jets proves to be efficient, this may bring a significant progress in the technological field.

Steady streaming in a turbulent oscillating boundary layer

2007 ◽  
Vol 571 ◽  
pp. 265-280 ◽  
Author(s):  
PIETRO SCANDURA
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Flow Rate ◽  
Stokes Equations ◽  
Infinite Plate ◽  
Harmonic Component ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Steady Streaming ◽  
Time Average

The turbulent flow generated by an oscillating pressure gradient close to an infinite plate is studied by means of numerical simulations of the Navier–Stokes equations to analyse the characteristics of the steady streaming generated within the boundary layer. When the pressure gradient that drives the flow is given by a single harmonic component, the time average over a cycle of the flow rate in the boundary layer takes both positive and negative values and the steady streaming computed by averaging the flow over n cycles tends to zero as n tends to infinity. On the other hand, when the pressure gradient is given by the sum of two harmonic components, with angular frequencies ω1 and ω2 = 2ω1, the time average over a cycle of the flow rate does not change sign. In this case steady streaming is generated within the boundary layer and it persists in the irrotational region. It is shown both theoretically and numerically that in spite of the presence of steady streaming, the time average over n cycles of the hydrodynamic force, acting per unit area of the plate, vanishes as n tends to infinity.

scholarly journals INVESTIGATION HYPERBOLIC PARABOLOID SHELL IN THE WIND TUNNEL AND COMPARISON WITH NUMERICAL SIMULATIONS

2018 ◽  
Vol 64 ◽  
Author(s):  
V.V. Stojanov ◽  
S. Jgalli
Keyword(s):  
Numerical Simulation ◽  
Wind Tunnel ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Wind Flow ◽  
Hyperbolic Paraboloid ◽  
Ansys Fluent ◽  
Navier Stokes Equations ◽  
Basic Model ◽  
The Impact

There are different ways to determine aerodynamic parameters, using analytical and experimental data for analyzing the behavior of structures when exposed to wind load. To date, the most developed is considered a numerical method for determining the characteristics of the above methods, based on the numerical solution of the Navier-Stokes equations. The accuracy of the results obtained using such a calculation method and obtaining the values of aerodynamic forces has increased due to the revision of mathematical models and the development of software complexes for the discretization of object bodies. This article gives an analytical overview of the results of research in the field of study the impact of wind loads on hypar (shell square in plan with the form of a hyperbolic paraboloid). The features of the investigated forms a discretization surface depending on pressure coefficients obtained in foreign literatures. Particular attention is paid to the numerical determination of aerodynamic coefficients on the surfaces of a hyperbolic paraboloid. The results were discussed and the nature of the distribution of coefficients depending on the angle of attack of the wind. Achieved analytical comparison computer modeling turbulent wind flows, based on solving the Reynolds equations arising from the use of averaging the Navier-Stokes equations. The basic model of turbulence such as: k-ε Standard Model; MMK; DBN; Shear-Stress Transport k-ω model; Transition k-kl-ω model. The possibility of choosing one or another model depending on the properties and characteristics of the wind flow is analyzed, for application in numerical simulation of wind flow around hyperbolic shells. The same was done, a comparative analysis of the results of physical testing in a wind tunnel with a numerical simulation in Ansys Fluent.

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