Simulation Of Three-dimensional Flow Research Articles

Three-dimensional numerical simulation of mud flow from a tailing dam failure across complex terrain

Abstract. A tailing dam accident can cause serious ecological disaster and property loss. Simulation of a tailing dam accident in advance is useful for understanding the tailing flow characteristics and assessing the possible extension of the impact area. In this paper, a three-dimensional (3-D) computational fluid dynamics (CFD) approach was proposed for reasonably and quickly predicting the flow routing and impact area of mud flow from a dam failure across 3-D terrain. The Navier–Stokes equations and the Bingham–Papanastasiou rheology model were employed as the governing equations and the constitutive model, respectively, and solved numerically in the finite volume method (FVM) scheme. The volume-of-fluid (VOF) method was used to track the interface between the tailings and air. The accuracy of the CFD model and the chosen numerical algorithm were validated using an analytical solution of the channel flow problem and a laboratory experiment on the dam-break problem reported in the literature. In each issue, the obtained results were very close to the analytical solutions or experimental values. The proposed approach was then applied to simulate two scenarios of tailing dam failures, one of which was the Feijão tailing dam that failed on 25 January 2019, and the simulated routing coincided well with the in situ investigation. Therefore, the proposed approach does well in simulating the flow phenomenon of tailings after a dam break, and the numerical results can be used for early warning of disasters and emergency response.

Reducing Undesired Wave Reflection at Domain Boundaries in 3D Finite Volume-Based Flow Simulations via Forcing Zones

This article reviews different types of forcing zones (sponge layers, damping zones, relaxation zones, etc.) as used in finite volume-based flow simulations to reduce undesired wave reflections at domain boundaries, with special focus on the case of strongly reflecting bodies subjected to long-crested incidence waves. Limitations and possible sources of errors are discussed. A novel forcing-zone arrangement is presented and validated via three-dimensional (3D) flow simulations. Furthermore, a recently published theory for predicting the forcing-zone behavior was investigated with regard to its relevance for practical 3D hydrodynamics problems. It was found that the theory can be used to optimally tune the case-dependent parameters of the forcing zones before running the simulations. 1. Introduction Wave reflections at the boundaries of the computational domain can cause significant errors in flow simulations, and must therefore be reduced. In contrast to boundary element codes, where much progress in this respect has been made decades ago (see e.g., Clement 1996; Grilli &Horillo 1997), for finite volume-based flow solvers, there are many unresolved questions, especially:How to reliably reduce reflections and disturbances from the domain boundaries?How to predict the amount of undesired wave reflection before running the simulation? This work aims to provide further insight to these questions for flow simulations based on Navier-Stokes-type equations (Reynolds-averaged Navier-Stokes, Euler equations, Large Eddy Simulations, etc.), when using forcing zones to reduce undesired reflections. The term "forcing zones" is used here to describe approaches that gradually force the solution in the vicinity of the boundary towards some reference solution, as described in Section 2; some examples are absorbing layers, sponge layers, damping zones, relaxation zones, or the Euler overlay method (Mayer et al. 1998; Park et al. 1999; Chen et al. 2006; Choi &Yoon 2009; Jacobsen et al. 2012; Kimet al. 2012; Schmitt & Elsaesser 2015; Perić & Abdel-Maksoud 2016a; Vukčević et al. 2016).

Computational fluid dynamics simulation of Hyperloop pod predicting laminar\u2013turbulent transition

Three-dimensional compressible flow simulations were conducted to develop a Hyperloop pod. The novelty is the usage of Gamma transition model, in which the transition from laminar to turbulent flow can be predicted. First, a mesh dependency study was undertaken, showing second-order convergence with respect to the mesh refinement. Second, an aerodynamic analysis for two designs, short and optimized, was conducted with the traveling speed 125 m/s at the system pressure 0.15 bar. The concept of the short model was to delay the transition to decrease the frictional drag; meanwhile that of the optimized design was to minimize the pressure drag by decreasing the frontal area and introduce the transition more toward the front of the pod. The computed results show that the transition of the short model occurred more on the rear side due to the pod shape, which resulted in 8% smaller frictional drag coefficient than that for the optimized model. The pressure drag for the optimized design was 24% smaller than that for the short design, half of which is due to the decrease in the frontal area, and the other half is due to the smoothed rear-end shape. The total drag for the optimized model was 14% smaller than that for the short model. Finally, the influence of the system pressure was investigated. As the system pressure and the Reynolds number increase, the frictional drag coefficient increases, and the transition point moves toward the front, which are the typical phenomena observed in the transition regime.

Axisymmetric and three-dimensional flow simulation of a mixed compression supersonic air inlet

The flow through an axisymmetric supersonic mixed-compression air inlet has been simulated numerically to investigate the effects and the necessity of the three-dimensional (3D) modeling in comparison with the axisymmetric one. For this purpose, a supersonic inlet has been simulated numerically via axisymmetric and 3D CFD solvers, using the steady state Reynolds-averaged Navier-Stokes equations along with the SST k-ω turbulence model, for a free-stream Mach number of 2.0 and at zero degrees angle of attack. The grid for the 3D cases was a 14.4-degree sector, instead of a 360-degree domain one, with rotational periodic boundary condition for the side boundaries. The results show that both static and total pressure distributions match well with the experimental data for both the axisymmetric and the 3D simulations. If the prediction of performance parameters is the main goal of simulations, it seems that the axisymmetric simulation provides adequate accuracy, and the 3D simulation one is not the best choice. The 3D numerical simulation results in an in-depth study on the supersonic inlets, including the shock wave-boundary layer interaction, the location of the terminal normal shock wave, and consequently the separation point. For an axisymmetric supersonic inlet in an axisymmetric flow condition, 3D effects are not strong enough to have a significant influence on the inlet performance for all operational conditions. However, it seems that 3D effects play an important role in both critical and supercritical operating conditions during the steady state operation.

The passage of a bubble or a drop past an obstruction in a channel

The passage of a fluid particle (bubble or a drop) past an obstruction in a rectangular channel is examined by numerical simulation, focusing on the disruption of the wake and the trajectory of the fluid particle. The flow is laminar, and the wake is initially steady. The obstruction is relatively large compared to the height of the channel. The problem is defined by the capillary number (Ca) and the Reynolds number (Re), the density (ηρ) and viscosity (ημ) ratios, and the relative size of the fluid particle (ηd). Simulations of three-dimensional flows are used to examine several combinations of these parameters. The results show that the motion of a drop is nearly independent of the wake downstream of the obstruction, but bubbles may get temporarily trapped in it. Drops also tend to block the background flow, while bubbles may accelerate it. It is found that a bubble of comparable or smaller size than the constriction can pass through the constriction intact without getting trapped. An increase in Ca and Re leads to bubbles passing through the constriction at a faster speed and move further downstream before being caught by the wake. Simulations of two-dimensional flows for a relatively larger range of Ca and Re are performed to obtain a flow regime diagram. The results show that relatively rigid particles (low Ca) tend to be temporarily trapped in the wake, while more deformable particles (higher Ca) pass without being trapped at lower Reynolds numbers but break up at higher Reynolds numbers. The influence of the obstruction geometry is also examined.

Numerical simulation of scour and flow field over movable bed induced by a submerged wall jet

Abstract Dam construction continues its rapid expansion around the world primarily for the purpose of hydropower generation. One important consequence of such projects is local scour at the downstream of the dam caused by outflow of excess reservoir water through spillways or bottom outlets that is associated with high velocities. The scour development endangers the dam foundation and river banks and undermines the stability of the hydraulic structures. In this study, a detailed three-dimensional (3D) flow simulation is conducted to investigate the complex fluid–sediment interactions leading to the formation of the scour hole and ridge systems downstream of a near-bottom jet. Three different bed-load equations, including Meyer-Peter–Müller, Nielsen, and Van Rijn formulas, are applied for calculating the bed-load transport rate. Comparison with a series of available experimental data shows that the Meyer-Peter–Müller equation results in better predictions than the two other relations. The performance of different turbulence models to reproduce vertical profiles of velocity and scour characteristic against the experimental data were evaluated. The vertical and horizontal profiles of the scour hole-ridge system are also compared with the corresponding experimental ones. The numerical model satisfactorily reproduces the geometric parameters representing the scour hole. However, the model overestimates the length of the scour hole.

Process of particles flow across staggered tubes in moving bed

Moving beds with staggered tubes are widely used in industrial applications to heat or cool solid particles. The heat transfer process is complicated and involves heat transfer amongst particles and between particles and tubes. Furthermore, the heat transfer mechanism is directly determined by the flow characteristics of particles across the outer surfaces of tubes because particles are the main heat carriers of particle flow. However, the particle flow across tubes is a kind of non-continuum flow, which is substantially different from Newtonian fluids, and the continuum theory is inappropriate for predicting particle flow in moving bed. In addition, little attention has been focused on this process. Thus, it is necessary to study the flow patterns of particles across tubes before studying the corresponding heat transfer mechanism. To describe this process, this work establishes a quasi-funnel flow (QFF) model, which can be used to calculate parameters, such as velocity field and residence time, by analyzing particle flow characteristics. The discrete element method (DEM) is used for a numerical simulation of three-dimensional particle flow across staggered tubes. The flow patterns, velocity field, typical particle trajectories and particle flow of local areas are obtained. Meanwhile, a moving bed experimental system is constructed, and the obtained results are used to verify the DEM numerical simulation results. Lastly, the results of the QFF model and that of the validated DEM numerical simulation are compared and found to be consistent. The ranges of the parameters required to describe the particle flow across tubes and the applicable range of the QFF model are also determined.

Three-dimensional simulation of two-phase flow in a complex gallery and telescopic pipe coupled system

Highly efficient cooling of heavy duty marine diesel engine pistons is one of the key parts of modern advanced engine piston design. Due to the high efficiency of the shaker cooling system, oil cooling galleries are extensively used. These galleries on low-speed marine engines are particularly complex, including a telescopic pipe and an air hole on the cross head. Few work has been done on coolant flow in such complex system under coupling of reciprocating, pressure and inertial force until now. The flow behaviour is relatively poorly understood. This study focuses on the influence of telescopic pipe on the two-phase flow details for a marine low-speed diesel engine. A 3D CFD model is established including both the piston gallery and a telescopic pipe. With this model, the change in the two-phase flow pattern with the progression of the crank angle was investigated, and the pressure and mass flow rate through typical sections of the oil cooling system were analysed. By changing the oil inlet pressure and crank shaft speed, key parameters characterising the flow pattern inside the galleries were compared. The numerical results demonstrate a strong correlation between the telescopic pipe and two-phase flow characteristics. Both decreasing the crank shaft speed and increasing the inlet pressure will reduce the backflow of outside air from the air hole boundary and increase the oil filling ratio. The proposed numerical model is able to predict the complex two-phase flow phenomenon in the gallery, which is important and provides a basis for further studies on the heat transfer mechanism and optimal design of the cooling system.

A mass-conserved multiphase lattice Boltzmann method based on high-order difference**Project supported by the National Natural Science Foundation of China (Grant Nos. 11862003 and 81860635), the Key Project of the Natural Science Foundation of Guangxi Zhuang Autonomous Region, China (Grant No. 2017GXNSFDA198038), the Project of Natural Science Foundation of Guangxi Zhuang Autonomous Region, China (Grant No. 2018GXNSFAA281302), the Project for Promotion

The Z–S–C multiphase lattice Boltzmann model [Zheng, Shu, and Chew (ZSC), J. Comput. Phys. 218, 353 (2006)] is favored due to its good stability, high efficiency, and large density ratio. However, in terms of mass conservation, this model is not satisfactory during the simulation computations. In this paper, a mass correction is introduced into the ZSC model to make up the mass leakage, while a high-order difference is used to calculate the gradient of the order parameter to improve the accuracy. To verify the improved model, several three-dimensional multiphase flow simulations are carried out, including a bubble in a stationary flow, the merging of two bubbles, and the bubble rising under buoyancy. The numerical simulations show that the results from the present model are in good agreement with those from previous experiments and simulations. The present model not only retains the good properties of the original ZSC model, but also achieves the mass conservation and higher accuracy.

Heat transfer and fluid flow of Biodiesel at a backward-Facing step

You should Three-dimensional simulation of a biodiesel fluid flow within a rectangular duct over a backward-facing step is investigated in the present paper. The fluid, which obeys to the Newtonian rheological behavior, is obtained by transformation of Algerian waste cooking oil into a biodiesel. Flow through a rectangular channel subjected to a constant wall temperature or constant heat flux as boundary conditions. The partial differential equations governing fluid flow and heat transfer are solved by the Fluent CFD computational code based on the Finite Volume Method. The numerical experiments are carried out to examine the effect of the Reynolds number by fluid inlet velocity variation for the two boundary conditions. The results are analyzed through the distribution of the temperature and the velocity contours. The variation of the Reynolds number and boundary conditions affects greatly the heat transfer and the fluid flow, in particular near the step region.

Three-dimensional numerical modelling of the flow around a circular bridge pier: a scaling analysis

Three-dimensional numerical simulations of water flow around a vertical circular pier using the 'large Eddy simulation' method are presented. All simulations were performed using the solver 'interFOAM' supplied with OpenFOAM. The objective of this paper is to provide a better understanding of the influence of the free-surface on the velocity and pressure fields. The influence of three parameters, the Froude number (Fr), the Reynolds number (Re) and the geometrical parameter G (ratio between the water depth and the pier diameter), on the behaviour of free-surface is investigated. Qualitative observations and quantitative results are reported. It is shown that downstream the pier, the flow depends on Fr and G. Indeed, a dimensionless number combination of Fr and G describes all the phenomena related with the free-surface deformation (the wavelength size, the free-surface deformation). On the contrary, for estimating the drag coefficient or for describing dynamic phenomena such as the separation of boundary layers in front of the pier a dimensionless number combination of Fr and Re must be used.

Simulation of the gas density distribution in the accelerator of the ELISE test facility.

In multiaperture electrostatic accelerators of negative ion sources, the plasma discharge is sustained by injecting gas in the plasma source, in a dynamic equilibrium with the gas flowing out through the accelerator. In this work, we present a three-dimensional numerical simulation of the gas flow inside the accelerator system of the large negative ion source ELISE at Max-Planck-Institut für Plasmaphysik Garching. ELISE has 640 apertures per electrode and lateral gaps between the electrode support structures that also contribute to the total gas conductance. Assuming molecular regime, we estimated the gas conductance, the gas density profile along the path of the ion beams from upstream of the plasma grid to downstream of the ground grid, and the transverse nonuniformities in the accelerator. The simulation included the most relevant geometrical features, while the results are compared to analytical results.

Fluid flow in the coat-hanger die: Validation of the fluid velocity at the die outlet

The melt blowing process has become one of the most important material processing methods due to its ability to produce a wide range of fabrics with a very fine fibrous structure. The design of the coat-hanger die is of the great importance in the melt blowing process, since the quality of the final product depends primarily on the flow homogeneity inside the die. The major objective of this study is to validate the reliability of the computational fluid dynamics technique when computing the velocity field at the die exit. Three-dimensional simulation of the fluid flow in the coat-hanger die was carried out using the Ansys Polyflow. The outcomes of the comprehensive simulation model were verified by the experimental results obtained by Meng et al. (2011). The simulation results showed good agreement with the experimental results of the melt velocity at the die exit. This implies that computational fluid dynamics modelling can accurately predict the behaviour of the polymer melt when properly utilized.

Three-dimensional numerical simulation of a turbulent flow around an obstacle

In this work we study the influence of the inclined shape of the lover and downstream edge of a rectangular obstacle. We analyze the dimensions of the recirculation zones, the velocity field, the kinetic energy and the pressure. A three-dimensional study was conducted using the ansys cfx calculation code. The turbulence model k-ԑ is used to model turbulence, and the governing equations are resolved by the finite volume method.

Three-dimensional numerical simulation of saturated annular flow boiling in a narrow rectangular microchannel

A fundamental numerical investigation on hydrodynamics and heat transfer performance of annular flow boiling in a rectangular microchannel with large width-to-depth ratio is performed in the paper. The saturation temperature recovery model based on the volume of fluid (VOF) method is implemented in OpenFOAM package to explore the heat transfer characteristics in annular flow regime with a three-dimensional computational domain. Validation of our methods has been conducted by comparing numerical results with experimental data. Effects of operating conditions including inlet mass flux, wall heat flux and inlet vapor quality are further discussed. It is found that the increase in wall heat flux or inlet quality will lead to the decrease of liquid thin film thickness between the interface and the heating wall. As the interfacial temperature is fixed at the saturation temperature, thinner liquid film will result in larger local heat transfer coefficient and lower wall temperature, which improves the heat transfer performance of the narrow microchannel. However, increasing the inlet mass flux will decrease the wall heat transfer coefficient, which is in accordance with the experimental result.

Three-dimensional simulation of gas-solid flow in a fluidised bed with flexible ribbon particles

Fluidisation is a widely used process in the industry as it offers high solid-gas contact efficiency and high heat and mass transfer, hence making it the unit operation of choice for drying. For instance, in the tobacco industry, drying of cut-tobacco is usually performed in fluidised beds. Unlike other particle materials, cut-tobacco exhibit ribbon-like morphology and are highly flexible. The high tendency of such particles to intertwine and form clusters could significantly influence the hydrodynamic characteristics and equipment performance. Therefore, it is of great significance to understand the dynamic behaviours of flexible ribbon particles in the fluidised bed. However, reported studies on such particles in the literature are scarce, and there is no large-scale numerical calculation for that matter. In this paper, the dynamic behaviours of flexible ribbon particles in a fluidised bed are investigated numerically using a two-way coupling of Discrete Element Method (DEM) and Computational fluid dynamics (CFD). A flexible ribbon chain model is used. The spring force constants is proposed and validated reasonably. Compared to other models, the flexible ribbon particle model provides better flexibility. It could also accurately reflect the flow properties of flexible ribbon particles to a certain extent. The effects of particle mass flow rate, superficial gas velocity and other process parameters on the particle dynamics in a fluidised bed are thoroughly studied in this paper. The numerical simulations are validated with experimental data, and the results show a very good agreement.

A closure model for the drag coefficient of a sphere translating in a viscoelastic fluid

In many large-scale industrial applications dealing with particle-laden viscoelastic fluids, the ensemble-averaged behavior of the mixture is of most interest. The first step to parametrize this behavior is to develop an accurate expression to rapidly evaluate the drag coefficient over a broad range of kinematic parameters. The drag coefficient of a spherical particle translating in a viscoelastic matrix is strongly affected by the viscoelasticity of the fluid. In this study, we aim to parametrize the effects of fluid elasticity, especially the relaxation and retardation times, as well as inertia on the drag coefficient of a sphere translating in a viscoelastic fluid described by the Oldroyd-B model. To this end, we employed three-dimensional direct numerical simulations of viscoelastic flow past a stationary sphere. The accuracy of the numerical formulation is thoroughly tested against a number of benchmark problems consisting of steady flow past a sphere in a bounded circular or square domain filled with either a Newtonian or viscoelastic fluid. Initially, the numerical computations for the drag coefficient over a wide range of geometric and flow parameters are validated by comparison with existing data and drag correction models from the literature. The drag coefficient correction is then evaluated for unconfined flow past a sphere at different Reynolds number, Re, over a wide range of Deborah number, De < 9, and polymer viscosity ratio, 0 < ζ < 1. For small Deborah number (De < 1), the drag coefficient decreases with respect to the Stokes drag coefficient, whereas, at large Deborah number (De > 1), the drag is enhanced due to the large elastic stresses that develop on both the surface and wake of the sphere. These canonical behaviors, observed in the inertia-less flow regime (Re ≤ 1) are amplified as the polymer viscosity ratio approaches unity. At higher Reynolds numbers (Re > 1), the drag coefficient correction arising from viscoelasticity is found to be always bigger than unity, but smaller than the enhancement calculated in the creeping flow limit. In this regime, the formation of an axisymmetric recirculating eddy expands the wake region behind the sphere, and shifts the maximum elastic stresses away from the rear stagnation point towards the flow separation points. Motivated by the self-similarity observed at Re < 1, we propose an approximate model for the viscoelastic drag coefficient based on rational functions, using the lowest possible degree of polynomial functions required to fit the computational data with 95% accuracy, for De ≤ 5 and 0 < ζ < 1. This expression is a key step towards formulating a momentum-exchange model for the flow of dilute suspensions of solid particles in a viscoelastic matrix.

Control of transitional shock wave boundary layer interaction using structurally constrained surface morphing

The potential of surface morphing techniques, including passive shock control bumps (SCB) and active surface morphing, is explored to control transitional shock wave boundary layer interactions (SWBLI). In addition to reducing the size of the separation bubble, a key objective is to mitigate the low-frequency unsteadiness that can cause detrimental structural response. To this end, three-dimensional flow simulations are performed using direct numerical simulations (DNS) at Mach 2 and Reynolds number based on inflow boundary layer thickness Reδin=996. An incident oblique shock of angle σ=35deg and strength p2/p1=1.4 impinges on a laminar boundary layer that evolves from a Blasius profile. The resulting boundary layer separation leads to transition and a Görtler-like instability is observed; the nominally two-dimensional and steady flow becomes three-dimensional and unsteady. The goal of this work is to develop a surface modification method to mitigate separation and low-frequency unsteadiness, which can trigger structural response and flow distortion. An aero-structural solver framework is developed and employed to examine both passive SCB and active surface morphing. To avoid unrealistic structural deformation in the transient or final states, the structural integrity is concurrently monitored so that the intermediate morphing solutions are restricted to achievable elastic deformations. The results indicate that transitional SWBLI can be controlled in this manner, to essentially inhibit transition and thus eliminate the separation and unsteadiness associated with the Görtler-like vortices. The mechanism modulates sharp increases in surface pressure at separation and shock-impingement locations encountered in uncontrolled SWBLI and results a lower specific entropy rise.

Improving water uptake by trees planted on a clayey soil and irrigated with low-quality water by various management means: A numerical study

The yield of avocado trees planted on clayey soils decreases due to irrigation with treated-waste water (TWW). We hypothesized that the main cause for this yield reduction is the reduction in water uptake by the trees roots. The aim of this numerical study was to identify the main soil factors that control the reduction in water uptake by the trees roots, and to test various soil substrate-based and water-based management schemes design to counterweigh the water uptake reduction. The study relies on physically based, three-dimensional (3-D) simulations of flow and transport in variably saturated, spatially heterogeneous, flow domain, conducted for three successive years. The main findings of this study suggest that: (i) the long-term effect of irrigation with TWW on the response of the flow system is attribute to the salinity of the TWW, and not to its sodium adsorption ratio, SAR; (ii) with respect to improving water uptake by the trees' roots, the water-based scheme that alternates irrigation water quality between TWW and desalinized water, DSW, (ADW) performed better than the water-based scheme that uses fresh water only (FW). The soil substrate-based schemes, TUFp, that used trenches with highly coarse-textured soil material and pulse irrigations, and, particularly, SAop, that used trenches with finer soil texture, performed substantially better than the soil substrate-based scheme that used trenches with highly coarse-textured soil material only (TUF); (iii) with respect to minimizing solute leaching below the root zone, the water-based schemes, FW, and, particularly, ADW, performed substantially better than the soil substrate-based schemes.

Numerical simulation for three-dimensional flow in a vortex tube with different turbulence models

Three-dimensional flow in a vortex tube with straight nozzle was investigated numerically. Four different turbulence models, Spalart-Allmaras, standard SST and realizable were proposed to replicate the flow in the vortex tube. The simulation results of pressure, temperature and velocity field were compared with the experimental data based on dimensionless analysis. It was found that the sudden gas expansion in the vortex chamber causes a pressure drop. The secondary circulations phenomena were observed and identified. Furthermore, the friction between the gas and wall surface and the energy transfer between different laminar flows are the main factors of energy separation in the vortex tube. The realizable model predicts energy separation better than other models studied in this research.