Showing papers in "Progress in Computational Fluid Dynamics in 2010"
TL;DR: In this article, the authors use the DEM to examine how variations of particle properties influence the performance of the screw conveyor and compare predicted mass flow rates with experimentally measured values.
Abstract: Screw conveyors are very effective for transporting dry particulates, giving good control over the throughput. Despite their apparent simplicity, the transportation action is very complex and designers have tended to rely heavily on empirical performance data. In this paper, we use the DEM to examine how variations of particle properties influence the performance of the screw conveyor. The primary focus of our study is comparing predicted mass flow rates with experimentally measured values. The secondary focus is to study how other performance measures (such as: particle speeds and power consumption) vary due to changes in the properties of the particles.
62 citations
TL;DR: In this paper, an approach to dealing with turbulent flows over a wall mounted cube using the wall y+ (non-dimensional distance from the wall) as guidance in selecting the appropriate grid configuration and corresponding turbulence models is investigated using FLUENT 6.3.
Abstract: An approach to dealing with turbulent flows over a wall mounted cube using the wall y+ (non-dimensional distance from the wall) as guidance in selecting the appropriate grid configuration and corresponding turbulence models is investigated using FLUENT 6.3. The study is divided into two sections – Case I and Case II, dealing with low and high Reynolds numbers, respectively. Five turbulence models – the standard k-e, standard k-ω, Reynolds Stress Model (RSM), Spalart-Allmaras (SA) and renormalisation group (RNG) k-e are used to solve the closure problem. Their behaviours, together with the accompanying near-wall treatments, are investigated for wall y+ covering the viscous sub-layer, the buffer layer and the log-law region.
36 citations
TL;DR: In this paper, steady-state two-dimensional CFD simulations of multiphase flow and heat transfer in the slag and air were carried out, and the thickness and temperature of a slag film prior to its rupture were predicted.
Abstract: Molten slag is atomised by a spinning disc into droplets that are quenched via cold air to produce glassy slag granules. Steady-state two-dimensional CFD simulations of the multiphase flow and heat transfer in the slag and air were carried out. Also considered in the CFD model is conjugate heat transfer between liquid slag, solidified slag and the disc. The thickness and temperature of the slag film prior to its rupture were predicted. Influence of factors including the slag pouring rate, temperature and the disc spinning speed on the slag film thickness and temperature were investigated.
34 citations
TL;DR: In this paper, a sliding mesh technique was employed within an entire stage of a multistage diffuser pump to investigate transient flow field and pressure fluctuations due to the interaction between impeller and diffuser vanes.
Abstract: In this work, three-dimensional, unsteady Reynolds-Averaged Navier?Stokes (RANS) equations with standard k-e turbulence models are solved by employing sliding mesh technique within an entire stage of a multistage diffuser pump to investigate transient flow field and pressure fluctuations due to the interaction between impeller and diffuser vanes. Sliding mesh calculation is carried out as the impeller zones slide (i.e., rotate) relative to diffuser zone along the grid interface in discrete time steps. The complicated time-periodic and spatial-periodic characteristics as well as rotor?stator interaction phenomena inside the pump stage are simulated and analysed to understand dynamic variation of the interior flow field and interference and finally to aim at optimal design.
25 citations
TL;DR: In this paper, the overall goal is to find out if Selective Non-Catalytic Reduction (SNCR) technologies can be used in grate-kiln plants for NOx reduction.
Abstract: The overall goal of this project is to find out if Selective Non-Catalytic Reduction (SNCR) technologies can be used in grate-kiln plants for NOx reduction. The technique has, to the best knowledge ...
24 citations
TL;DR: In this article, a two-equation Shear Stress Transport (SST) turbulence model coupled with curvature correction was used to predict the mean flow behavior inside a hydrocyclone.
Abstract: Turbulence analysis of flow inside a hydrocyclone is carried out using commercially available CFD software ANSYS CFX (release 11.0) (ANSYS Inc., 2007). CFD software(s) and their turbulence models have come a long way in accurately predicting the flow inside a hydrocyclone. This paper shows, among various turbulence models tested, a two-equation Shear Stress Transport (SST) turbulence model coupled with curvature correction can accurately predict the mean flow behaviour. The same level of accuracy was only found with a SSG Reynolds stress model with a penalty of solving an additional five transport equations. Experimental data of Hsieh (1988) and Monredon et al. (1992) was used to validate our CFD models.
20 citations
TL;DR: In this article, the effects of varying the impeller blade pitch angle and the gap size between the rotor and housing were investigated for axial pump performance and the level of shear-related blood damage.
Abstract: This study involves simulation of blood flow through a non-pulsatile, axial pump consisting of a complex multi-sectioned impeller with rotating and stationary components, and a stationary housing. We use a particle-based method, Smoothed Particle Hydrodynamics (SPH), to investigate the effects of varying the impeller blade pitch angle and the gap size between the rotor and housing. We show that the impeller blade inclination affects pump performance and the level of shear-related blood damage. The inclusion of a rotor-housing clearance results in flow losses that reduce the efficiency of the pump but also reduce the viscous energy losses in the pump.
16 citations
TL;DR: In this article, the Lapple cyclone was studied numerically and validated experimentally and eight geometric configurations for improving the operation of the annular ejector were evaluated, with the result that compressible, time-dependent CFD results were extremely sensitive to the pressure discretisation approach and to the differential Reynolds Stress pressure strain formulation.
Abstract: Unsteady flow features of a plant-scale (>1.5 m diameter) cyclone-ejector system have been studied numerically and validated experimentally. Complexity arises from the fact that the transient pressure field within the Lapple cyclone governs the operation of the annular ejector, and vice versa. Eight geometric configurations for improving the system operation were evaluated. Simple geometric changes were shown numerically to make operational improvements while incrementally improving particle collection efficiency. It was also found that compressible, time-dependent CFD results were extremely sensitive to the pressure discretisation approach and to the differential Reynolds Stress pressure strain formulation.
15 citations
TL;DR: In this article, a methodology is developed for the analysis of diesel engine in-cylinder processes and combustion and an integrated KIVA-3V code is developed by incorporating two well-validated models into the standard code: the Shell hydrocarbon auto-ignition model and the Characteristic-time model for simulation of subsequent diesel combustion.
Abstract: A methodology is developed for the analysis of diesel engine in-cylinder processes and combustion. Beginning from CAD data of the engine geometry, the methodology involves use of a commercial code AVL FIRE for simulation of suction stroke, and an open-source code KIVA-3V for simulation of the closed-valve part of the diesel cycle. For this, an algorithm is first developed to map a generalised three-dimensional Computational Fluid Dynamics (CFD) solution from an unstructured mesh in AVL FIRE to a structured mesh in KIVA-3V to provide initial conditions for the closed-valve simulations. For simulation of diesel combustion process, an integrated KIVA-3V code is developed by incorporating two well-validated models into the standard code: the Shell hydrocarbon auto-ignition model for simulation of diesel auto-ignition under conditions of high temperature and pressure, and the Characteristic-time model for simulation of subsequent diesel combustion. The integrated code is validated and calibrated against experimental pressure measurements in a naturally aspirated direct injection diesel engine. These tools are then used for exploring the potential of a constant-speed, turbocharged diesel engine towards emission reduction. The case study involves combustion simulations for exploring multiple injection strategy for the engine concerned.
12 citations
TL;DR: In this paper, a new approach has been presented to solve gas-liquid flow numerically in vertical pipes of air-lift pumps, which is achieved via applying a novel scheme called the Physical Influence Scheme (PIS).
Abstract: A new approach has been presented to solve gas-liquid flow numerically in vertical pipes of air-lift pumps. To improve modelling, a new strategy has been employed with the capability of coupling the continuity and momentum equations and enforcing the role of pressure directly in the continuity equation. This is achieved via applying a novel scheme called the Physical Influence Scheme (PIS). The current finite volume solution is compared with other available numerical solutions. Indeed, they are in fair agreement. However, the present predictions are far superior to those obtained from an existing simple method, which is widely used in airlift pump modelling.
11 citations
TL;DR: In this paper, the effect of wind fairings on the experimental results of a simplified Tractor/Trailer model is analyzed and it is proposed that a separation occurs on the floor behind the vehicle, which results in the experimentally observed large vortex structure.
Abstract: In this paper, the effect of the wind fairings (model support coverings) on the experimental results of a simplified Tractor/Trailer model is analysed. It is proposed that a separation occurs on the floor behind the vehicle, which results in the experimentally observed large vortex structure. Time-averaged URANS results in 0.1-1.0 s indicate that the RNG k-e model captures unsteady flow structure, formed by the interaction of the bluff-body wake and the Von Karman vortices behind the cylindrical posts forming the large vortex structure behind the wind tunnel test model. Comparison of average velocity fields and streamline structures indicate agreement with the experimental results.
TL;DR: In this paper, the viscous flow characteristics around a typical radar antenna cross-section were analyzed via computations and a parametric study of possible new shape designs for the antenna was discussed.
Abstract: Modern air traffic control systems in airports use high-speed ground tracking radars usually rotating at 60 rpm. The flow induced vibration and noise generation of the newly developed radar antennas are the two serious problems that jeopardise the successful deployment of the ground aircraft tracking systems. The present study is an attempt to understand the viscous flow characteristics around a typical radar antenna cross section via computations. After a steady-state validation of the computations, a parametric study of possible new shape designs for the antenna is discussed. Significant aerodynamic drag reductions via careful shape design of the antenna are possible.
TL;DR: In this paper, a single cylinder and two paratactic cylinders in nanoscale were investigated in the view of discrete particles, and transient and temporal-averaged flow and density fields were obtained to analyse the wake flow.
Abstract: Obstructed flow around single cylinder and two paratactic cylinders in nanoscale were investigated in the view of discrete particles. Transient and temporal-averaged flow and density fields were obtained to analyse the wake flow. For single cylinder case, Stokes flow, steady vortex flow, periodic vortex-shedding flow with the Karman vortex street and supersonic flow were distinguished based on Re. For two paratactic cylinders case, periodic vortex-shedding flow, periodic vortex-shedding flow with gap-flow, bistable flow and synchronised vortex-shedding flow were observed with different centre-to-centre pitch ratios. Despite of some special characteristics, the results indicate most macroscopic flow patterns still exist in nanoscale.
TL;DR: In this paper, the authors used the commercial CFD software, STAR-CD, to model pneumatic conveying in a horizontal pipe and obtained reasonable agreement between the predicted pressure drop and the experimental data of Marcus et al. (1990) for spherical particles and Vasquez et al (2008) for non-spherical particles.
Abstract: Pneumatic conveying of solid materials is used in many process industries where solid particles are carried forward in pipes and channels by the fluid. The pressure drop in the system is dependent on a host of parameters such as particle and pipe diameters, particle and fluid properties, pipe roughness and orientation, etc. In this study, the commercial CFD software, STAR-CD is used to model pneumatic conveying in a horizontal pipe. A range of fluid flow rates is studied. Reasonable agreement is obtained between the predicted pressure drop and the experimental data of Marcus et al. (1990) for spherical particles and Vasquez et al. (2008) for non-spherical particles. The sensitivity of the computed results to particle properties and the choice of fluid drag model are also studied.
TL;DR: In this paper, a comprehensive simulation model is introduced where representative droplets are traced in a Lagrangian manner while the dust is treated as passive Eulerian phases, and the wall film is considered by a model solving the shallow water equations, including models for droplet deposition, film separation and film stripping.
Abstract: In a wet scrubber water is introduced into dust laden off-gas in order to capture the fine dust particles. The scrubbing process comprises a whole set of phenomena like droplet break-up, coalescence, liquid wall film and dust capturing. We introduce a comprehensive simulation model is where representative droplets are traced in a Lagrangian manner while the dust is treated as passive Eulerian phases. The wall film is considered by a model solving the shallow water equations, including models for droplet deposition, film separation and film stripping. Numerical results for pressure drop and capturing efficiency are in good agreement with measurements.
TL;DR: In this paper, the dynamics of flow past a circular cylinder is investigated at Reynolds number (Re) between 20 and 3900 using the rectangular mesh and two interpolation techniques, namely bi-linear proposed by the authors and unidirectional quadratic by Muldoon and Acharya, are compared for both the laminar and the turbulent flow regime.
Abstract: The dynamics of flow past a circular cylinder is investigated at Reynolds number (Re) between 20 and 3900 using the rectangular mesh. The Re is defined based on the cylinder diameter D and the free-stream velocity U∞. This is achieved by using the Immersed Boundary (IB) method that helps to impose boundary conditions on a given surface not coinciding with the computational grid. Two interpolation techniques, namely bi-linear proposed by the authors and unidirectional quadratic by Muldoon and Acharya (2005), are compared for both the laminar and the turbulent flow regime. The unsteady Navier?Stokes (N?S) equations are solved using a symmetry-preserving finite-difference scheme of second-order spatial and temporal accuracy. Large-Eddy Simulations (LES) with the dynamic subgrid model are used to resolve the turbulent flow at Re = 1000 and 3900. When compared with experiments, it reveals that the IB method is worth pursuing and both the interpolations generate almost identical results for a wide range of Reynolds numbers. The bi-linear interpolation is easy to implement and take less computational time because of its simplicity.
TL;DR: In this paper, the effect of furnace crater pressure on the melt and gas flows inside the submerged arc furnaces used for silicon production is investigated, and a multiphase flow model predicts how the gas pressure in the furnace crater zone can affect the metal flows at the furnace bottom, the gas flow pattern inside the charge materials, the metal tapping flow rate and the flow rate from the furnace taphole.
Abstract: In this paper the effect of furnace crater pressure on the melt and gas flows inside the submerged arc furnaces used for silicon production is investigated. The multiphase flow model predicts how the gas pressure in the furnace crater zone can affect the metal flows at the furnace bottom, the gas flow pattern inside the charge materials, the metal tapping flow rate and the gas flow rate from the furnace taphole. The model also shows that gas blow out from the tap hole can change the gas flow pattern inside the charge materials all the way to the furnace top.
TL;DR: The authors corrected a mistake in the authors' previous paper (Nakaoka et al., Progress in Computational Fluid Dynamics, 2008, 8(5), 270-275), which originated in the solution procedure of the population-balance (PB) equation.
Abstract: This paper is to correct a mistake in the authors' previous paper (Nakaoka et al., Progress in Computational Fluid Dynamics, 2008, 8(5), 270-275), which originated in the solution procedure of the population-balance (PB) equation.
TL;DR: In this paper, the grid-free Smoothed Particle Hydrodynamics method with its Lagrangian framework is used to predict the oxide mass generated during a melt transfer from a tilting furnace into a sow mold.
Abstract: Aluminium melt transfer operations lead to dross formation via splashing/turbulence. Optimisation may be achieved by employing computational modelling to explore the effects of various process parameters. Existing mesh-based modelling techniques are limited due to their inability to carry history information such as accumulated oxide mass per-node. Instead, the grid-free Smoothed Particle Hydrodynamics method with its Lagrangian framework is used to predict the oxide mass generated during a melt transfer from a tilting furnace into a sow mould. An oxidation model based on laboratory-scale skimming trials is used. Favourable comparisons with experimentally measured oxide levels are obtained for various transfer rates.
TL;DR: In this article, conductive, convective and radiative heat transfer models were added in the commercial Computational Fluid Dynamics (CFD) code ANSYS CFX, to describe the interaction between the porous solid and the fluid.
Abstract: Porous burners offer potential for ultra-lean methane emission mitigation by combustion. In these systems, heat recirculation between the porous medium and the fuel stream leads to enhanced combustion behaviour. In this research, conductive, convective and radiative heat transfer models were added in the commercial Computational Fluid Dynamics (CFD) code ANSYS CFX, to describe the interaction between the porous solid and the fluid. Relatively detailed skeletal kinetic mechanisms were implemented and a stiff chemistry solver was used to account for the differing chemical and fluid dynamics timescales. Results from test cases are presented to illustrate the model performance and to highlight some computational issues.
TL;DR: In this paper, a new model for the prediction of the windage and breathing losses was presented, and applied to the blow-by flow model for improving the CO2 emissions from internal combustion engines.
Abstract: The reduction of CO2 emissions from internal combustion engines by increasing their efficiency becomes more and more important. Improved efficiency may be achieved by decreasing ventilation losses due to the pumping in the crankcase. Computational Fluid Dynamics (CFD) was rarely used for simulating the crankcase flow so far. This work presents a new model for the prediction of the windage and breathing losses, and applies a model for the blow-by flow. The complete moving crank drive is resolved. The simulation of one engine cycle shows the complex three-dimensional gas flow field, resulting in the crank angle resolved ventilation loss moment.
TL;DR: In this article, the authors investigated three-dimensional fluid flow and heat transfer for flow past a square cylinder built-in a rectangular channel and solved the governing equations for viscous fluid flow with the help of an indigenously developed computational code based on modified MAC algorithm.
Abstract: Present work investigates three-dimensional fluid flow and heat transfer for flow past a square cylinder built-in a rectangular channel. The governing equations for viscous fluid flow and heat transfer are solved numerically with the help of an indigenously developed computational code based on modified MAC algorithm. Unsteady computations are performed for Reynolds number in the range of 400-1000 and channel height ranging from 0.5d to 3d (d being side of the square cylinder). The effect of channel height on onset of vortex shedding, other flow characteristics and heat transfer from heated solid surfaces has been presented.
TL;DR: In this paper, the growth of short-wave elliptical instabilities in a Lamb-Oseen vortex pair subject to non-uniform strain fields at close vortex spacing was considered using direct numerical simulation at a Reynolds number Re = 20000.
Abstract: The growth of short-wave elliptical instabilities in a Lamb-Oseen vortex pair subject to non-uniform strain fields at close vortex spacing is considered using direct numerical simulation at a Reynolds number Re = 20000. A linear stability analysis demonstrates that with reduced vortex spacing the growth rate of all axial wave-numbers is enhanced relative to that of the fastest-growing mode. A coupling of vortices is observed at close vortex spacing, which may lead to improved non-linear instability growth, and the development of fluid cross-over regions. These fluid cross-over regions are shown to be products of a linear growth regime.
TL;DR: In this article, a global model was developed to investigate the effect of crystal and crucible rotations in absence and presence of the Electromagnetic Fields (EMs) on melt flow.
Abstract: Oxygen content in the pure Silicon crystal is inevitable because of the significant rate of corrosion of the crucible walls at high temperature. Precise control of oxygen is possible only by manipulating underlying flow. A global model was developed to investigate the effect of crystal and crucible rotations in absence and presence of the Electromagnetic Fields (EMs) on melt flow. The simulation results show that strong buoyancy driven flow interaction generates non-uniformity in oxygen concentration near the edge of the crystal in the absence of magnetic field. Application of external field facilitates more pumping of melt underneath the crystal that prevents stratification of oxygen near the edge.
TL;DR: In this paper, computational fluid dynamics (CFD) has been used to investigate the combustion processes occurring within a rotary lime kiln and found that firing the kiln with a 25/ thermal substitution of waste oil is the most efficient mode of operation.
Abstract: Computational Fluid Dynamics (CFD) has been used to investigate the combustion processes occurring within a rotary lime kiln Numerical results were validated against experimental data from the International Flame Research Foundation's (IFRF) Furnace No 1 Results highlighted the need to reduce cold air leakages into the kiln and that firing the kiln with a 25/ thermal substitution of waste oil is the most efficient mode of operation The work presented in this article will enable operating and environmental costs of the rotary kiln to be reduced and has laid the foundation for further investigations into the combustion of waste fuels in rotary kilns
TL;DR: In this paper, a liquid-air blast atomiser continuously discharges within a test section of air at atmospheric pressure, with and without a circular cylinder placed 25 diameters (D = 10 mm) downstream of the nozzle.
Abstract: This study determines the intrusiveness of endoscopic tools within multiphase flows. A liquid-air blast atomiser continuously discharges within a test section of air at atmospheric pressure, with and without a circular cylinder placed 25 diameters (D = 10 mm) downstream of the nozzle. Data was collected using Particle Image Velocimetry (PIV), drop sizing and Computational Fluid Dynamics (CFD). Numerical predictions are compared against the PIV results for wake flow characterisation. Using a non-intrusive droplet sizing technique it has been observed that the average droplet diameter increases when the circular cylinder is introduced and so does the frequency of occurrence of these large particles. Smaller particles are re-circulated, whereas the larger drops continued in the general direction of the spray cone.
TL;DR: In this paper, the authors used the Large Eddy Simulation (LES) technique to study velocity and passive scalar mixing along with intermittency of a spatially evolving turbulent coaxial swirl jet.
Abstract: This work uses the Large Eddy Simulation (LES) technique to study velocity and passive scalar mixing along with intermittency of a spatially evolving turbulent coaxial swirl jet. The simulations captured the potential core and also predicted high level turbulence intensities in the inner mixing regions. The Probability Density Functions (PDFs) and radial intermittency plots revealed an intermittent mixing behaviour especially in the outer region of the flow where the fluctuations of velocity rapidly change from rotational to irrotational and vice versa. The PDF and radial intermittency profiles exhibit Gaussian and non-Gaussian distributions close to the jet centreline and away from the centreline, respectively.
TL;DR: In this paper, the authors simulated steady and unsteady natural convection flows of a nanofluid in a square cavity and showed that the particle migration model predicts negligible non-uniformities in the particle distribution.
Abstract: We simulated steady and unsteady natural convection flows of a nanofluid in a square cavity. If the particle distribution is perfectly uniform there is a reduction of the heat transfer rates of about 1% in comparison with those corresponding to the pure liquid. The Lagrangian tracking of the particles shows that there is no preferential concentration of particles. However the local instantaneous fluctuations of the particle concentration induced by the tracking of a finite number of particles produce reductions of the heat transfer rates of about 2-3%. The particle migration model used predicts negligible non-uniformities in the particle distribution.
TL;DR: In this article, the turbulent dispersion of a passive scalar released from a continuous ground-level point-source in two obstacle arrays is simulated using the Reynolds-averaged Navier-Stokes (RANS) method.
Abstract: In this paper, the turbulent dispersion of a passive scalar released from a continuous ground-level point-source in two obstacle arrays is simulated using the Reynolds-averaged Navier-Stokes (RANS) method. An explicit algebraic nonlinear turbulent stress model and a tensor-diffusivity scalar-flux model are used for the closure of the ensemble-averaged momentum and scalar transport equations, respectively. The principal physical mechanisms governing the transport of the second-order concentration statistics of a passive scalar are modelled following Yee et al. (2009). The results of the simulation for the flow and concentration statistics are compared against two sets of high-quality water-channel measurement data obtained using laser induced fluorescence (for concentration) and laser Doppler anemometry (for velocity).
TL;DR: The Parallel MNIM (PMNIM) is developed in order to further enhance its capabilities and it is observed that significant memory effects in the computations with variable problem size result in efficiencies greater than one.
Abstract: A Modified Nodal Integral Method (MNIM) for three-dimensional, incompressible Navier-Stokes (N-S) equations has recently been developed. MNIM requires relatively less number of grid points for the desired accuracy. The Parallel MNIM (PMNIM) is developed in order to further enhance its capabilities. Since template of the nodal integral method is quite different from those that result from finite volume schemes, parallelisation of a nodal code has unique challenges. The PMNIM is applied to a test problem to evaluate its performance. It is observed that significant memory effects in the computations with variable problem size result in efficiencies greater than one.