Darrin Stephens

Darrin Stephens
Applied CCM

PhD

About

49
Publications
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209
Citations

Publications

Publications (49)
Article
As the expectations for more consistent and higher density thickened and paste tailings in the minerals industry increase, so do the demands on flocculation performance within gravity thickeners. Low solids feed suspensions are delivered at a high velocity to center feedwells, which not only serve to dissipate the feed’s momentum and evenly distrib...
Conference Paper
For over 25 years, the AMIRA P266 “Improving Thickener Technology” series of projects sought to advance fundamental understanding of all aspects of gravity thickening towards achieving better operational performance. Detailed studies of flocculation were complemented with mathematical and computational modelling, as well as both pilot and full-scal...
Article
Aqueous solutions (∼0.01–0.2%) of long chain polymers are used during gravity thickening to aggregate particle suspensions. These polymers are often dosed into turbulent flow through submerged pipes (sparges) to maximise their distribution. At high concentrations, these viscoelastic solutions mix poorly with surrounding flows unless highly diluted....
Conference Paper
Many tailings slurries are comprised of fine particles suspended in a carrier fluid (usually water). For high enough concentrations, the fines and water combine to form a non-Newtonian slurry. In a number of important applications, these slurries also contain larger, denser particles that are able to settle under shear. This results in inhomogeneit...
Conference Paper
Full-text available
The emphasis of this paper is on the validation and verification of the open source numerical library, Caelus, suitable for the simulation of problems in continuum physics. The focus of this work is the verification and validation of problems in fluid mechanics. Several test cases including Couette and Kovasznay flows are used in verification of th...
Conference Paper
Full-text available
In this work verification and validation of Reynolds Averaged Navier-Stokes (RANS) turbulence models for incompressible flows were performed on the numerical library, Caelus [1]. Caelus is free and open source licensed under the GNU Public License (GPL). The focus of this study is on the verification and validation of the k-w SST [2, 3], Spalart-Al...
Conference Paper
The addition of a Nutrient Reduction Plant (NRP) to the 55E primary treatment pond in the Western Treatment Plant (WTP) in Werribee, Victoria, has been proposed by Melbourne Water and is currently undergoing studies to confirm its configuration. The feed being drawn in has the potential to impact the hydraulics and patterns of flow within the 25W/5...
Conference Paper
Full-text available
Cyclones play a dominant role in the industrial separation of dilute particles from an incoming gas flow. The complex swirling flow in cyclones provides significant challenges for turbulence modelling in CFD. This paper presents a single phase transient solver developed using the Caelus library. The solver predictions using k-ω SST with and without...
Conference Paper
Full-text available
Bluff body shapes are used to promote better heat and mass transfer in various industrial flow situations, flow past them serving to enhance turbulence and thereby promote mixing, primarily due to the vortex shedding created. In this paper, the turbulent mixing fields for flow past a square sparge jet is investigated both experimentally and numeric...
Conference Paper
Full-text available
Turbulence is a phenomenon that occurs frequently in nature and is present in almost all industrial applications. Despite significant increase in computational power in modern processors, Reynolds averaged Navier-Stokes (RANS) simulations are still the dominant approach to turbulence modelling of high Reynolds number flows. Hybrid LES/RANS approach...
Conference Paper
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Bubble columns are widely used in the chemical and biochemical process industries. In order to develop design tools for engineering purposes, a large amount of research has been carried out in the area of CFD of gas-liquid flows. In this paper a transient Euler-Lagrange solver developed using the open source Caelus library is used to simulate the g...
Conference Paper
Full-text available
With increasing demand for water for industrial and residential usage, wastewater treatment represents a major engineering challenge. Fine solids removal is mainly achieved through gravity decantation: waste effluents enter large tanks, from which clarified water overflows and concentrated settled solids are pumped from the bottom. For sludges cont...
Conference Paper
Full-text available
This paper presents a fast transient solver suitable for the simulation of incom-pressible flows. The main characteristic of the solver is that it is based on the projection method and requires only one pressure and momentum solve per time step. Furthermore, advantage of using the projection method in the formulation is the particularly efficient f...
Conference Paper
Full-text available
This paper presents a fast transient solver suitable for the simulation of transient turbulent flows. The main characteristic of the solver is that it is based on the projection method and requires only one pressure and the momentum solve per time step. Furthermore, using the projection method has the additional advantage that the formulation of th...
Article
CFD modelling offers powerful simulation capability, but only provides information for a given design and set of process conditions. While it allows comparison between different outcomes, CFD results alone do not provide an optimised outcome. In many design problems, thousands of function evaluations may be required to undertake an optimisation stu...
Article
Computer modelling has been used extensively in some processes in the sugar industry to achieve significant gains. This paper reviews the investigations carried out over approximately the last twenty five years, including the successes but also areas where problems and delays have been encountered. In that time the capability of both hardware and s...
Conference Paper
Full-text available
Adjoint equations for the incompressible turbulent Navier-Stokes equations are presented. The main characteristic of this adjoint formulation is that it is time symmetry preserving thus kinetic energy conservative. The newly formulated equations were applied to the computation of surface shape sensitivities of an Australian V8 supercar. Three cases...
Conference Paper
Full-text available
Computational Fluid Dynamics (CFD) modelling offers powerful simulation capability, but only provides information for a given design and set of process conditions. While it allows comparison between different outcomes, CFD results alone do not provide an optimised outcome. The computational cost associated with the use of high-fidelity CFD models p...
Conference Paper
Full-text available
Shape derivative based on topological consideration is presented in this work. The resulting derivative has simpler form compared to corresponding classical shape derivative due to topological derivative formulation. Shape derivative is based on topological derivative in the limit of infinitesimally weak source terms in momentum equation approachin...
Article
Computational Fluid Dynamics (CFD) has played a crucial role in enabling the design and scale-up of the HIsmelt <sup align="right"> ® </sup> direct iron smelting technology. An existing PHOENICS-based CFD model of the molten bath dynamics in the process vessel has been transferred to ANSYS-CFX to improve its accuracy and to enable efficient analysi...
Conference Paper
Full-text available
CFD has played a crucial role in enabling the design and scale-up of the HIsmelt® direct smelting technology. The HIsmelt® Process is a potential replacement for blast-furnace technology owing to its efficiency, cost advantage and lower environmental impact. An existing PHOENICS-based CFD model of the molten bath dynamics in the process vessel has...
Conference Paper
Full-text available
A three node quadrature method of moments (QMOM) population balance model was implemented in an Algebraic Slip Multiphase model in the ANSYS CFX (release 12) Computational Fluid Dynamics (CFD) package for the simulation of gibbsite precipitation. The population balance model included the effects of agglomeration, molecular growth and secondary nucl...
Conference Paper
Full-text available
Advanced Computational Fluid Dynamics (CFD) modelling techniques are well suited for examining suspension flow patterns within feedwells and thickeners from which improved design options can be developed and evaluated. However, the confidence to rely upon recommendations based upon CFD requires model validation, something that is not readily achiev...
Article
a b s t r a c t The computational cost associated with the use of high-fidelity computational fluid dynamics (CFD) models poses a serious impediment to the successful application of formal sensitivity analysis in engineering design. Even though advances in computing hardware and parallel processing have reduced costs by orders of magnitude over the...
Conference Paper
Full-text available
The Quadrature Method of Moments (QMOM) Population Balance technique was implemented in a CFD 2-D axisymmetric plug-flow pipe reactor for gibbsite precipitation to simulate the evolution of the moments of the Crystal Size Distribution (CSD). Incorporated into the model are the effects of nucleation, growth and agglomeration on the evolution of mome...
Article
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 She...
Article
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 She...
Conference Paper
Full-text available
The computational cost associated with the use of high-fidelity Computational Fluid Dynamics (CFD) models poses a serious impediment to the successful application of formal sensitivity analysis in engineering design. Even though advances in computing hardware and parallel processing have reduced costs by orders of magnitude over the last few decade...
Conference Paper
Full-text available
Turbulence analysis of flow inside a hydrocyclone is carried out using commercially available CFD software ANSYS-CFX (release 11.0). Commercial CFD software(s) and their turbulence models have come a long way in accurately predicting the flow inside a hydrocyclone, both at the mean as well as at the turbulence level. Previous studies have shown, th...
Conference Paper
Full-text available
A Computational Fluid Dynamics (CFD) model for modelling a floating phase has been developed and tested on a settling tank. The current model used for settling tanks is able to predict the settling of solids and the formation of a higher density layer of solids at the bottom of the vessel. Due to the widespread use of settling tanks in water and ot...
Conference Paper
Full-text available
Single phase modelling studies have been carried out using commercially available software ANSYS-CFX (release 11.0) on a laboratory scale thickener feedwell geometry. With the increase in complexity of feedwell and thickener geometries, meshing with a hexahedral mesh is time-consuming and sometimes impossible. The first objective of this study is t...
Conference Paper
Full-text available
As the expectations for more consistent and higher density thickened and paste tailings increase, so do the demands on thickener performance. Over the last 20 years, the AMIRA P266 “Improving Thickener Technology” series of projects, have significantly advanced the understanding of thickening by combining fundamental investigations of flocculation,...
Article
Full-text available
This work reports on the use of numerical optimisation techniques to optimise objective functions calculated by Computational Fluid Dynamics (CFD) simulations. Two example applications are described, the first being the shape optimisation of a low speed wind tunnel contraction. A potential flow and viscous flow solver have been coupled to produce a...
Conference Paper
Full-text available
A computational fluid dynamics (CFD) solver ANSYS- CFX is used to model the heat transfer in the region near the surface of a leach heap when drippers are buried. The potential for natural convection to occur above the dripper level, thus substantially increasing heat loss from the heap, is investigated. A parameter analysis is performed which show...
Conference Paper
Full-text available
Numerical and especially CFD modelling are becoming cost-effective and reliable ways to develop improvements in vessel designs. Simulating boiling in crystallisation vacuum pans is a very complex process that needs to consider non-isothermal conditions, multi-component, multiphase boiling and condensation. This level of complexity which has been ca...
Conference Paper
Full-text available
The heat transfer and condensation of steam within the steam belt and the steam chest surrounding the calandria tubes of vacuum pans and evaporators were investigated using computational fluid dynamics (CFD) modelling techniques. The flow of steam in evaporators and vacuum pans is an aspect that is not usually given much attention but it can influe...
Conference Paper
Full-text available
Broadwater Sugar Mill commissioned a 4000 m 2 SRI-designed Roberts evaporator for the 2002 crush. The evaporator is the crucial first stage of a cogeneration plant, which will comprise a high-pressure boiler and turbo-alternator producing renewable electrical energy for sale. To achieve this, steam consumption by all process plant will need to be m...
Conference Paper
Full-text available
A heat transfer model of boiling flow in steam heated calandria tubes is presented. The model predictions for vapour formation, heat transfer and pressure difference are compared with experimental data and yield reasonable agreement. Characteristic curves are presented showing predicted evaporation rate, heat transfer and pressure difference for a...
Conference Paper
Full-text available
A method for using 'hot film' anemometers to determine circulation velocities within vacuum pans has been refined and tested on a number of pans during trials performed over the 2001 season. The anemometers have been used to characterise circulation velocity profiles that can be used to validate computer models and illustrate the differences among...
Thesis
Full-text available
This thesis presents an investigation into mathematical modelling of natural circulation in high grade batch vacuum pans. Batch vacuum pans are an important part of a sugar factory, with the circulation in such vessels being a key factor in successful sucrose extraction. The flow within a batch vacuum pan is laminar with three phases (molasses, cry...
Conference Paper
Full-text available
One-and two-dimensional numerical models of forced convective boiling of molasses in a calandria tube are described. The flow in the tube is considered to be composed of two phases (molasses and steam). The one-dimensional model solves a simplified set of ODEs describing the non-equilibrium boiling process. The two-dimensional model is based on the...
Article
This paper explores a simple test problem that can be used as a benchmark solution for Eulerian two-phase flow CFD models. Results are presented for a commercial CFD code with multiphase flow capability, namely CFX-4.2, produced by AEA Technology. The results show that CFX-4.2 exhibits virtually perfect agreement for all 17 test cases covering a wi...

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Project (1)
Project
While there have been several published overset implementations based on OpenFOAM, none to date have been either available to the public or have a general suite of capabilities. Caelus is a freely available fork of OpenFOAM that was launched in 2014. The overset framework will be able to handle static, prescribed, constrained and unconstrained dynamic motions. For the latter, a 6-DoF ODE solver with a wide selection of integrators and constraints will be developed. The library was developed such that enabling overset in an existing solver requires modifying only a few lines of code. It uses Suggar++, from Celeritas Simulation Technology, for hole cutting, interpolation stencil computations and other overset grid assembly tasks.