Finite Volume Numerical Simulations Research Articles

P‐86: Prediction of Droplet Behavior in Piezoelectric Inkjet Printing Based on Waveguide Theory

In the present study, we numerically investigate the effect of sub‐pulse addition on the applied voltage waveform on the high‐speed jetting procedure of drop‐on‐demand inkjet printing. The concept of a waveguide was adopted to model the reflective and interference properties of sound waves in complex geometrical layout of the pump structure partially surrounded by the piezoelectric actuator. We proposed a nonlinear model in which the mass is concentrated in points by dividing the fluid column and the connecting duct inside the pump section into equal‐sized volumetric elements. A three‐dimensional finite volume numerical simulation was performed for the solution of the Navier‐Stokes equation based on the volume‐of‐fluid method for tracing the fluid interface. The negative part of the bipolar waveform acts as a suction‐removal residual pressure, suppressing the satellite, while the positive voltage repels the meniscus and separates the liquid from the meniscus. The present method based on waveguide theory was successfully applied to evaluate the effect of multi‐step waveform voltage in terms of maximum velocity, size, satellite generation, ligament length.

Forecasting the energy characteristics of a reversible hydraulic machine for a head up to 250 m

BACKGROUND: At present, in the pressure zone of 50650 m for pumped storage power plants, hydroelectric units with classic single-stage radial-axial reversible hydraulic machines, which have a relatively simple design of the impeller and cylindrical guide vane, have received the most widespread energy performance, but are relatively quiet, large-sized and metal-intensive hydraulic machines. Numerical research and design of this type of machines are given special attention. The current trend is the design of flow parts based on numerical simulation of the flow. The most well-known commercial software products that implement finite volume numerical simulations are Ansys Fluent, Ansys CFX, StarCD, Numeca, Flow Vision and CADRUN. In the work under consideration, the calculations were performed using the Ansys CFX software package version 2021R1. Today, due to the lack of numerical capacity, the task of developing and using a technique that will allow obtaining an acceptable result with optimal time spent on data preparation and computational studies remains an urgent task.
 AIMS: The aim of the work was to present an economical methodology for numerical simulation of energy characteristics.
 METHODS: The methodology consists in describing the problem statement, the computational grids used, and the assumptions made for the optimal use of computing resources without a significant loss in the accuracy of the results.
 Object of computational research: The presented article investigates the flow part of a radial-axial pump-turbine designed for application to a maximum head of up to 250 m.
 RESULTS: Numerical modeling of power characteristics of on-pump and turbine modes is performed. A brief description of the problem statement, computational grids used, and assumptions made is given. A comparison of calculation results with experimental data of model tests is presented. The comparison results are presented in the relative form for the main parameters: pressure, efficiency, reduced rotational speed and flow rate.
 CONCLUSIONS: It is recommended to use SST model of turbulence in a stationary statement in order to predict the power characteristics of pump-turbines. The use of economical block-structured grids, as well as the performing of calculations only in the region of one blade of the guide vanes, one impeller blade and a suction pipe with the use of preliminary results of calculations in a spiral chamber allow using computational resources optimally without significant loss of accuracy of the results.

Secondary Cooling Analysis of AZ80Y Magnesium Alloy Slab during DC Casting by Modelling and Verification Based on Experiment

The secondary cooling of AZ80 during DC casting was investigated by measuring the temperature at a given position during steady state. The experiment was carried out under different parameters including the water flow rate density (Q*) and initial temperature (Ti) of the impingement points. To theorize the heat transfer of the secondary cooling zone in practical DC casting, we designed a series of experimental equipment to simulate the secondary cooling with differing Ti (between 473 and 673 K) and Q* (between 20 and 100 L min−1 m−1) based on the DC casting temperature-measurement experiment above. Detailed analysis was carried out of both the experimental results combined with Q*. The empirical formulae of Rohsenow and Weckman were modified due to the need to divide the secondary cooling zone into an impingement zone and a free-falling zone. Finally, a verification of the model’s accuracy was conducted by comparing the results of the finite volume numerical simulation and the experiment, which revealed that the model exhibited extremely high accuracy.

Quasi-static CFD research of the spool flow valve parameters

ABSTRACT This paper presents the results of the flow rate characteristics study of the new design liquid flow valve. Data were obtained using finite volume numerical simulation in the OpenFOAM package of the spatial flow of liquid in the flow part of the valve. A simplified quasi-static approach was used, which allowed obtaining results at low-cost computing resources. One of the purposes was to show the reason for the difference in the flow-drop characteristic obtained experimentally and from the previously calculated one-dimensional mathematical model. It was found that the coefficient of hydrodynamic force, got in the OpenFOAM package, is greater than is accepted in the one-dimensional model.

Improved Calculation of Wellblock Pressures for Numerical Simulation of Non-Newtonian Polymer Injection

Summary The viability of any enhanced-oil-recovery project depends on the ability to inject the displacing fluid at an economic rate. This is typically evaluated using finite-volume numerical simulation. These simulators calculate injectivity using the Peaceman method (Peaceman 1978), which assumes that flow is Newtonian. Most polymer solutions exhibit some degree of non-Newtonian behavior resulting in a changing polymer viscosity with distance from the injection well. For shear-thinning polymer solutions, conventional simulations can overpredict injection-well bottomhole pressure (BHP) by several hundred psi, unless a computationally costly local grid refinement is used in the near-wellbore region. We show theoretically and numerically that the Peaceman pressure-equivalent radius, based on Darcy flow, is not correct when fluids are shear thinning, and derive an analytical expression for calculating the correct radius. The expression does not depend on any particular functional relationship between polymer-solution viscosity and velocity. We test it using the relationship described by the Meter equation (Meter and Bird 1964) and the Cannella et al. (1988) correlation. Numerical tests indicate that the solution provides a significant improvement in the accuracy of BHP calculations for conventional numerical simulation, reducing or removing the need for expensive local grid refinement around the well when simulating the injection of fluids with shear-thinning non-Newtonian rheology.

The effect of straight chimney temperature on pollutant dispersion

Air pollution is considered one of the most important contemporary problems that threaten a person's life and environment. Among the major sources of air pollution are pollutants emitted from smokestacks. The objective of this work is to numerically study the dispersion of a pollutant ejected from a chimney into an air stream. The mass, momentum and energy conservation equations are solved using the finite volume method (MFV) and numerical simulations are performed using Ansys Fluent CFD software. Two case studies were discussed: The first case study is to study the influence of the direction of the wind speed and in the last case study, the temperature evolution on the dispersion of the ejected plume particles. The study demonstrated the extent of the dispersion in relation to these two parameters. The results obtained confirm the need to improve filtering systems in order to reduce the risks attributed to discharges and to propose solutions to manage the effect of these discharges on the environmental population.

Predicting the Behaviour of a Vortex Shedding-Based Passive Mechanical Micro Heat Exchanger

In the recent years, microscale applications are gaining increasing importance. Despite their advances, the technology and resources needed to develop new designs may be a drawback for reduced scale engineering testing. To overcome this, computational methods are an efficient tool to predict how a real-life system may behave prior physical construction. The present work aims to investigate numerically effective models to predict the conditions at which a micro heat exchanger (MHE) is able to promote mixing by vortex shedding mechanics. In spite of vortex-shedding is a well-known mechanism in flow physics, it is not possible to know a priori whether a configuration (for a given geometry and flow velocity) may or may not lead to this desired vortex detachment to enhace mixing. Thus, Machine Learning methods are used for prediction, trained with finite-volume numerical simulations of different MHE devices selected based on their performance. A classification model is used to predict which configurations lead to vortex shedding. Also, a correlation regression model is developed to predict the critical Reynolds number. When the critical Reynolds number is surpassed for a given geometry, vortex shedding appears and its intensity controls the thermal mixing efficiency of the microdevice. These predictors could be useful in the search of optimal configurations by optimisation algorithms, since in the sampling process could be used to define constrains.

COMPUTATION OF GOLD-WATER NANOFLUID NATURAL CONVECTION IN A THREE-DIMENSIONAL TILTED PRISMATIC SOLAR ENCLOSURE WITH ASPECT RATIO AND VOLUME FRACTION EFFECTS

Nanofluids are increasingly being deployed in numerous energy applications owing to their impressive thermal enhancement properties. Motivated by these developments in the current study we present finite volume numerical simulations of natural convection in an inclined 3-dimensional prismatic direct absorber solar collector (DASC)containing gold-water nanofluid. Steady-state, incompressible laminar Newtonian viscous flow is assumed. The enclosure has two adiabatic walls, one hot (solar receiving) and one colder wall. ANSYS FLUENT software(version 19.1) is employed. The Tiwari-Das volume fraction nanofluid model is utilized to simulate nanoscale effects and allows a systematic exploration of volume fraction effects. The effects of thermal buoyancy (Rayleighnumber), geometrical aspect ratio and enclosure tilt angle on isotherm and temperature contour distributions are presented with extensive visualizationin three dimensions. Grid-independence tests are included. Validation with published studies from the literature is also conducted. A significant modification in vortex structure and temperature distribution is computed with volume fraction, Rayleigh number, aspect ratio and tilt angle. Heat flux and average Nusselt number results are also included. Gold nano-particles even at relatively low volume fractions are observed to achieve substantial improvement in heat transfer characteristics.

Inflow performance relationship of vertical wells in fractured vuggy media during semi-steady state flow regime

The inflow performance relationship (IPR) is one of the essential key parameters that control the fluids production/injection rate from wells. The presence of the vugs in addition to fractures in carbonate reservoirs introduce many difficulties related the estimation of IPR of future wells. In this study, a novel analytical IPR of dual-permeability, triple porosity model is derived for the first time. The introduced IPR formula is derived for the standard scenario model of a vertical and fully penetrating well in a circular reservoir under single-phase flow of slightly compressible fluid. The three governing flow equations (matrix flow equation, fracture flow equation and interaction between vugs and other two continuum equation) are solved simultaneously as a system of differential equations for semi-steady state (SSS) flow regime. The generated SSS IPR is the same as Darcy's straight line IPR multiplied by an error parameter (E23) which is bounded between zero and one. A detailed investigation of the effect of the reservoir petro-physical parameters like storativities, inter-porosities and fracture to matrix permeability ratio are presented. The newly presented IPR of dual-permeability, triple porosity system can be reduced to sub-models IPRs by further modification of error parameter to fit sub-model as single permeability, triple porosity (E13) or dual permeability, dual porosity (E22). The presented IPR formula has the advantage of dividing the pressure drop of the fluid flow to two components, one for the internal resistance between different continuums (which is resented by E) and the other one is the radial flow in the same continuum toward/from well-bore. The generated IPR model is double verified using both cell pressure centred finite volume numerical simulation and conventional pressure transient analysis.

Nanofluids and converging flow passages: A synergetic conjugate-heat-transfer enhancement of micro heat sinks

Simultaneous effects of using nanoparticle (Al2O3) in water along with the converging flow passages on the forced convection heat transfer coefficient in a microchannel heat sink (MCHS) are investigated using a finite volume numerical simulation. The accurate KKL (Koo-Kleinstreuer-Li) model, considering particles' material density, volume fraction, diameter and Brownian motion, is implemented to model the thermophysical properties of Al2O3-water nanofluid. The numerical simulation is performed based on a non-uniform structured grid. Results have shown that nanoparticles can enhance the convection heat transfer coefficient of the base fluid and the enhancement obtained by the nanoparticles are 33% higher for the case of the converging flow passages than that of straight passages. Simulation results have proved that implementation of an enhanced working fluid (i.e. Al2O3-water nanofluid) and using geometrical enhancement (i.e. converging flow passages) reveal synergetic thermal response and shows an effective enhancement on the convection heat transfer coefficient as high as 2.35 times greater than the heat transfer coefficient of a pure water flows through a straight channel with no convergence. The present results suggest implementing nanofluids along with converging flow passages to achieve the effective enhancement in the convection heat transfer coefficient and to boost the improvement obtained by each individual enhancement technique, especially in the thermally developed regions wherein the convection heat transfer coefficient cannot be increased by increasing the inlet velocity/pressure in the laminar flow regime.

Development of convection in high temperature coil annealing furnaces using rotating cylinder technique

The present study investigates the usage of rotating cylinders to generate gas circulation inside high-temperature coil annealing furnaces during the annealing treatment of grain-oriented electrical steel. This technique has been investigated to reduce temperature differentials (hotspots) within the furnace space, a phenomenon that occurs due to extremely high temperatures, the static nature of the gas inside of the furnace and long operation conditions. Finite volume numerical simulation using ANSYS Fluent was performed to test the validity of the proposed technique. The numerical results showed fluctuations in velocity magnitude of the fluid in comparison with a case when the technique was not employed. This is because of the vortex generation under the effect of the cylinder rotation. The generation of turbulence enhances gas-mixing quality, and thus it would save a great amount of energy required for the process, producing a product with desired magnetic properties at lower cost.

Prediction of Convective Heat Transfer Coefficient and Temperature Distribution of Air-Conditioned Spaces Using Numerical Simulation

Accurate and efficient modeling of convective heat transfer coefficient (CHTC) by considering the detailed room geometry and heat flux density in building is demanding for economy, environmental amiability, and user satisfaction. We report the three-dimensional finite-volume numerical simulation of internal room flow field characteristics with heated walls. Two different room geometries are chosen to determine the CHTC and temperature distribution. The conservation equations (elliptic partial differential) for the incompressible fluid flows are numerically solved using iterative method with no-slip boundary conditions to compute velocity components, pressure, temperature, turbulent kinetic energy, and dissipation rate. A line-by-line solution technique combined with a tri-diagonal matrix algorithm (TDMA) is used. The temperature field is simulated for various combinations of air-change per hour and geometrical parameters. The values of HTCs are found to enhance with increasing wall temperatures.

Transport of a dilute active suspension in pressure-driven channel flow

Confined suspensions of active particles show peculiar dynamics characterized by wall accumulation, as well as upstream swimming, centreline depletion and shear trapping when a pressure-driven flow is imposed. We use theory and numerical simulations to investigate the effects of confinement and non-uniform shear on the dynamics of a dilute suspension of Brownian active swimmers by incorporating a detailed treatment of boundary conditions within a simple kinetic model where the configuration of the suspension is described using a conservation equation for the probability distribution function of particle positions and orientations, and where particle–particle and particle–wall hydrodynamic interactions are neglected. Based on this model, we first investigate the effects of confinement in the absence of flow, in which case the dynamics is governed by a swimming Péclet number, or ratio of the persistence length of particle trajectories over the channel width, and a second swimmer-specific parameter whose inverse measures the strength of propulsion. In the limit of weak and strong propulsion, asymptotic expressions for the full distribution function are derived. For finite propulsion, analytical expressions for the concentration and polarization profiles are also obtained using a truncated moment expansion of the distribution function. In agreement with experimental observations, the existence of a concentration/polarization boundary layer in wide channels is reported and characterized, suggesting that wall accumulation in active suspensions is primarily a kinematic effect that does not require hydrodynamic interactions. Next, we show that application of a pressure-driven Poiseuille flow leads to net upstream swimming of the particles relative to the flow, and an analytical expression for the mean upstream velocity is derived in the weak-flow limit. In stronger imposed flows, we also predict the formation of a depletion layer near the channel centreline, due to cross-streamline migration of the swimming particles towards high-shear regions where they become trapped, and an asymptotic analysis in the strong-flow limit is used to obtain a scale for the depletion layer thickness and to rationalize the non-monotonic dependence of the intensity of depletion upon flow rate. Our theoretical predictions are all shown to be in excellent agreement with finite-volume numerical simulations of the kinetic model, and are also supported by recent experiments on bacterial suspensions in microfluidic devices.

Investigation of turbulence model and numerical scheme combinations for practical finite-volume large eddy simulations

Large eddy simulation (LES) is known to suffer from two primary error sources – the subgrid stress (SGS) model and the numerical discretization scheme. These cannot be separately quantified for finite-volume numerical simulations, but an appropriate combination can yield ‘engineering accurate’ prediction of turbulence dynamics. This paper seeks to evaluate combinations of commonly used second-order numerical schemes and Smagorinsky-type SGS models for practical LES. Error assessments are performed for isotropic decaying turbulence using both pseudospectral and finite-volume solvers, followed by validation for a complex turbulent flow of engineering interest. Error assessment using pseudospectral techniques is performed to isolate finite-differencing and modeling errors by explicitly adding numerical derivative error terms to the simulations. Error assessment using the finite-volume method focuses on identification of optimal model-discretization combinations for the best LES predictions using application solvers. The pseudospectral and finite-volume approaches show consistent predicted behavior of the interplay between numerical and modeling errors for different model-discretization combinations. Of those studied here, the two most optimal combinations are identified as: (1) standard or dynamic Smagorinsky SGS model with a bounded central difference scheme; and (2) Monotonic Integrated LES (MILES) with either a second-order upwind or QUICK scheme. These combinations were applied for an axisymmetric jet flow at Re ∼ 105, using an ‘engineering quality’ mesh, where the MILES model with either an upwind or QUICK scheme showed the best predictive capability.

Computational analysis of natural convection in a parallelogrammic cavity with a hot concentric circular cylinder moving at different vertical locations

A finite volume numerical simulation of natural convection in a parallelogrammic air-filled cavity having a heated concentric circular cylinder is performed. The left and right sidewalls of the cavity are maintained at a uniform cold temperature, while both upper and lower walls of it are considered thermally insulated. A wide range of significant parameters such as Rayleigh number, inclination angle and cylinder vertical locations are considered in the present study. Comparison with previously published works is made and found to be an excellent agreement. The results show that the strength of the flow circulation and the thickness of thermal boundary layer around the hot circular cylinder are increased dramatically when the Rayleigh number increases. Also, to increase the flow circulation inside the parallelogrammic cavity, it is recommended to make the inner cylinder moves downward until it reaches to [δ=−0.2] and the parallelogrammic cavity sidewalls inclined to [Φ =15°]. Moreover, it is found that for various values of the inclination angle, the average Nusselt numbers at inner cylinder surface and at both cavity sidewalls, decrease when the cylinder moves upward, while they increase when the cylinder moves downward.

Analysis of a finite volume method for a bone growth system in vivo

This paper is devoted to the convergence analysis of a finite volume method and numerical simulations of a reaction–cross diffusion system arising from a bone growth model. This model describes the evolution of mesenchymal stem cells, osteoblasts, bone matrix and osteogenic growth factor. We propose a numerical scheme based on an implicit finite volume method constructed on an orthogonal mesh. Lack of the regularity of the approximate system is overcome by stability results which allow to obtain estimates on the translates, apply the Kolmogorov theorem in order to get compactness and show the convergence of the proposed scheme. The efficiency and robustness of the scheme are shown in simulating a situation in bone growth: the healing of a skull fracture in rats.

Study on Superalloy Tube Extrusion Process Using Finite Volume Method

In this paper, complexity of the process of high temperature alloy tubing extrusion is studied using the Finite Volume Method (FVM). We establish mathematical model of high temperature alloy tube extrusion process by using the Finite Volume Method. We develop the simulation program by the control equation of the Finite Volume Method and numerical simulation of the key technologies of the axisymmetric problem in cylindrical coordinates. Inconel690 high temperature alloy tubing extrusion process, for example, we got the squeeze pressure in the steady-state extrusion, Velocity field and the corresponding equivalent strain rate field. By comparing the results obtained by the finite volume method and simulation results from Finite Element Method (FEM) software on DEFORM-2D, we find our mathematical model on high temperature alloy tubing extrusion process is reasonable and correct.

Modelling of interfacial mass transfer in microfluidic solvent extraction: part I. Heterogenous transport

An investigation of molecular diffusion of solutes across water/oil interfaces in a Y-Y-shaped microchannel with an integrated guide structure is presented. Finite volume numerical simulations were compared with experimental literature data. Analytical approaches including an infinite composite medium model, phase-specific mass transfer coefficient models, and a static transfer cell model were also assessed. An increase in accuracy for the mass transfer coefficient models was achieved by using local coefficients as opposed to length-averaged expressions. The static transfer cell model was shown to improve when based on the interfacial contact time, as opposed to the organic phase residence time. The results presented in this work have immediate application to the determination of kinetic rate constants in reactive mass transfer systems, as considered in Part II of this study (Ciceri et al. Microfluid Nanofluid, 2012).

Analysis of free and forced convection in airflow windows using numerical simulation of heat transfer

The present paper describes a two-dimensional finite volume numerical simulation of flow and heat transfer in airflow windows by free and forced convection techniques. The governing equations are the fully elliptic, Reynolds-averaged Navier–Stokes equations. The simple algorithm is employed to correct the pressure term. The second-order upwind scheme is used to discretize the convection terms. The (k-e/RNG) turbulence model is applied for the flow simulation. The mesh used is the body-fitted, multi-plane grid system. Results on the variations of velocity and temperature profiles with geometrical parameters, at different temperature and velocity, for heat transfer by free and forced convection techniques are presented. Comparisons of the present results on temperature distribution for forced convection and for free convection with the available experimental forced convection data indicate that the airflow-influenced forced convection methods are considerably enhanced.

A reduced finite volume element formulation and numerical simulations based on POD for parabolic problems

A proper orthogonal decomposition (POD) method is applied to a usual finite volume element (FVE) formulation for parabolic equations such that it is reduced to a POD FVE formulation with lower dimensions and high enough accuracy. The error estimates between the reduced POD FVE solution and the usual FVE solution are analyzed. It is shown by numerical examples that the results of numerical computation are consistent with theoretical conclusions. Moreover, it is also shown that the reduced POD FVE formulation based on POD method is both feasible and highly efficient.