# Publications

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## 2015 |

Stephens, Darrin W; Sideroff, Chris; Jemcov, Aleksandar Simulation and validation of turbulent gas flow in a cyclone using Caelus Conference Eleventh International Conference on CFD in the Minerals and Process Industries, 2015. Abstract | Links | BibTeX | Tags: Caelus, Cyclone, Turbulence, Validation @conference{Stephens2015b, title = {Simulation and validation of turbulent gas flow in a cyclone using Caelus}, author = {Darrin W Stephens and Chris Sideroff and Aleksandar Jemcov}, url = {https://www.researchgate.net/publication/286417605_SIMULATION_AND_VALIDATION_OF_TURBULENT_GAS_FLOW_IN_A_CYCLONE_USING_CAELUS}, year = {2015}, date = {2015-12-09}, booktitle = {Eleventh International Conference on CFD in the Minerals and Process Industries}, abstract = {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 curvature corrections, Reynolds Stress Model (LRR) and Large Eddy Simulation (Smagorinsky and coherent structure) turbulence models are compared against laser velocity measurements to investigate the level of accuracy afforded by each turbulence model. The k-ω SST model without any curvature corrections produced the poorest predictions of the flow field, whilst the coherent structure LES was found to be in excellent agreement with the experimental measurements.}, keywords = {Caelus, Cyclone, Turbulence, Validation}, pubstate = {published}, tppubtype = {conference} } 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 curvature corrections, Reynolds Stress Model (LRR) and Large Eddy Simulation (Smagorinsky and coherent structure) turbulence models are compared against laser velocity measurements to investigate the level of accuracy afforded by each turbulence model. The k-ω SST model without any curvature corrections produced the poorest predictions of the flow field, whilst the coherent structure LES was found to be in excellent agreement with the experimental measurements. |

Stephens, Darrin W; Sideroff, Chris; Jemcov, Aleksandar Simulation and validation of turbulent gas flow in a cyclone using Caelus Presentation 09.12.2015. Abstract | Links | BibTeX | Tags: Caelus, Cyclone, Turbulence, Validation @misc{Stephens2015b, title = {Simulation and validation of turbulent gas flow in a cyclone using Caelus}, author = {Darrin W Stephens and Chris Sideroff and Aleksandar Jemcov}, url = {http://www.appliedccm.com/wp-content/uploads/2015/12/CFD2015-DWS.pdf}, year = {2015}, date = {2015-12-09}, abstract = {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 curvature corrections, Reynolds Stress Model (LRR) and Large Eddy Simulation (Smagorinsky and coherent structure) turbulence models are compared against laser velocity measurements to investigate the level of accuracy afforded by each turbulence model. The k-ω SST model without any curvature corrections produced the poorest predictions of the flow field, whilst the coherent structure LES was found to be in excellent agreement with the experimental measurements.}, keywords = {Caelus, Cyclone, Turbulence, Validation}, pubstate = {published}, tppubtype = {presentation} } 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 curvature corrections, Reynolds Stress Model (LRR) and Large Eddy Simulation (Smagorinsky and coherent structure) turbulence models are compared against laser velocity measurements to investigate the level of accuracy afforded by each turbulence model. The k-ω SST model without any curvature corrections produced the poorest predictions of the flow field, whilst the coherent structure LES was found to be in excellent agreement with the experimental measurements. |

Mohanarangam, Krishna; Stephens, Darrin W; Cao, Xiaodong; Fawell, Phillip D; Simic, Kosta; Yang, William Experimental and numerical investigation of turbulent mixing fields behind bluff body jets Conference Eleventh International Conference on CFD in the Minerals and Process Industries, 2015. Abstract | BibTeX | Tags: OpenFOAM, PIV, Turbulence, Validation @conference{MOHANARANGAM2015, title = {Experimental and numerical investigation of turbulent mixing fields behind bluff body jets}, author = {Krishna Mohanarangam and Darrin W Stephens and Xiaodong Cao and Phillip D. Fawell and Kosta Simic and William Yang}, year = {2015}, date = {2015-12-07}, booktitle = {Eleventh International Conference on CFD in the Minerals and Process Industries}, abstract = {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 numerically. The geometry considered for this study was a square channel fitted with a square sparge located midway along its length. Time Resolved – Particle Image Velocimetry (TR-PIV) measurements were conducted to measure and quantify the mixing and the turbulent fields behind the sparge. Measurements were carried out at a frequency of 1 KHz to capture the unsteady behaviour of the flow past the sparge and its jet. Computational Fluid Dynamics (CFD) simulation of the set-up was carried out by solving Unsteady Reynolds Averaged Navier Stokes (URANS) equations with the k-ω model as turbulence closure. Various ratios between the bulk flow past the sparge and that of its jet were considered to investigate the turbulent behaviour of the sparge geometry, while also providing data for model development and calibration. The long-term aim is to identify sparge designs that provide enhanced mixing in industrial flow settings.}, keywords = {OpenFOAM, PIV, Turbulence, Validation}, pubstate = {published}, tppubtype = {conference} } 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 numerically. The geometry considered for this study was a square channel fitted with a square sparge located midway along its length. Time Resolved – Particle Image Velocimetry (TR-PIV) measurements were conducted to measure and quantify the mixing and the turbulent fields behind the sparge. Measurements were carried out at a frequency of 1 KHz to capture the unsteady behaviour of the flow past the sparge and its jet. Computational Fluid Dynamics (CFD) simulation of the set-up was carried out by solving Unsteady Reynolds Averaged Navier Stokes (URANS) equations with the k-ω model as turbulence closure. Various ratios between the bulk flow past the sparge and that of its jet were considered to investigate the turbulent behaviour of the sparge geometry, while also providing data for model development and calibration. The long-term aim is to identify sparge designs that provide enhanced mixing in industrial flow settings. |

Stephens, Darrin W; Sideroff, Chris; Jemcov, Aleksandar A two equation VLES turbulence model with near-wall delayed behaviour Conference 7th Asia-Pacific International Symposium on Aerospace Technology, 25 – 27 November 2015, Cairns, 2015. Abstract | Links | BibTeX | Tags: Caelus, LES, RANS, Rudimentary Landing Gear, Square cylinder, Turbulence, VLES, Vortex shedding @conference{Stephens2015b, title = {A two equation VLES turbulence model with near-wall delayed behaviour}, author = {Darrin W Stephens and Chris Sideroff and Aleksandar Jemcov}, doi = {10.13140/RG.2.1.1791.1125}, year = {2015}, date = {2015-11-25}, booktitle = {7th Asia-Pacific International Symposium on Aerospace Technology, 25 – 27 November 2015, Cairns}, abstract = {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 approaches [1] are currently used to offset the cost of Large Eddy Simulation (LES) computations by retaining the RANS characteristics in boundary layers while using the LES model away from walls. The hybrid approach embodied in the Detached Eddy Simulation (DES) methodology has been used with success in industrial flow simulations. However, it should be noted that the DES approach still requires LES-like mesh resolution away from walls. This is a simple consequence of the fact that the DES model defaults to LES at large distances from the walls. This may prove prohibitively expensive in simulations where large turbulent structures persists over most of the computational domain. In this work, a delayed two equation very large eddy simulation (VLES) model based on three length scales is introduced. The resolution control function used to rescale the Reynolds stresses is based on the ratio of the resolved to unresolved turbulence spectrum. The model constants are selected so that the Smagorinsky subgrid-scale model is recovered in the limit of grids approaching the resolution required for LES computations. The near wall RANS behaviour of the proposed model is obtained using blending functions. The objective was to implement this model using the open source library Caelus [2] and validate the results against two test cases involving turbulent vortex shedding from a bluff-body. The test cases used were flow past a square cylinder at a Reynolds number of 21,400 [3] and the Rudimentary Landing Gear benchmark case for Airframe Noise Computations (BANC) [4]. The numerical simulations were carried out using a transient solver based on the open source computational mechanics library Caelus. The pressure-based solver with second-order bounded spatial discretisation and second-order bounded implicit time marching scheme was applied to obtain a time-accurate solutions. Compressibility effects were negligible for the Mach numbers under consideration and the flow was treated as incompressible. Results from the simulations indicate close agreement between the proposed model and available experimental and numerical results. }, keywords = {Caelus, LES, RANS, Rudimentary Landing Gear, Square cylinder, Turbulence, VLES, Vortex shedding}, pubstate = {published}, tppubtype = {conference} } 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 approaches [1] are currently used to offset the cost of Large Eddy Simulation (LES) computations by retaining the RANS characteristics in boundary layers while using the LES model away from walls. The hybrid approach embodied in the Detached Eddy Simulation (DES) methodology has been used with success in industrial flow simulations. However, it should be noted that the DES approach still requires LES-like mesh resolution away from walls. This is a simple consequence of the fact that the DES model defaults to LES at large distances from the walls. This may prove prohibitively expensive in simulations where large turbulent structures persists over most of the computational domain. In this work, a delayed two equation very large eddy simulation (VLES) model based on three length scales is introduced. The resolution control function used to rescale the Reynolds stresses is based on the ratio of the resolved to unresolved turbulence spectrum. The model constants are selected so that the Smagorinsky subgrid-scale model is recovered in the limit of grids approaching the resolution required for LES computations. The near wall RANS behaviour of the proposed model is obtained using blending functions. The objective was to implement this model using the open source library Caelus [2] and validate the results against two test cases involving turbulent vortex shedding from a bluff-body. The test cases used were flow past a square cylinder at a Reynolds number of 21,400 [3] and the Rudimentary Landing Gear benchmark case for Airframe Noise Computations (BANC) [4]. The numerical simulations were carried out using a transient solver based on the open source computational mechanics library Caelus. The pressure-based solver with second-order bounded spatial discretisation and second-order bounded implicit time marching scheme was applied to obtain a time-accurate solutions. Compressibility effects were negligible for the Mach numbers under consideration and the flow was treated as incompressible. Results from the simulations indicate close agreement between the proposed model and available experimental and numerical results. |

Stephens, Darrin W; Sideroff, Chris; Jemcov, Aleksandar A two equation VLES turbulence model with near-wall delayed behaviour Presentation 25.11.2015. Abstract | Links | BibTeX | Tags: Caelus, LES, RANS, Rudimentary Landing Gear, Square cylinder, Turbulence, VLES, Vortex shedding @misc{Stephens2015b, title = {A two equation VLES turbulence model with near-wall delayed behaviour}, author = {Darrin W Stephens and Chris Sideroff and Aleksandar Jemcov}, url = {http://www.appliedccm.com/wp-content/uploads/2015/11/APISAT-2015-PPT.pdf}, year = {2015}, date = {2015-11-25}, abstract = {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 approaches [1] are currently used to offset the cost of Large Eddy Simulation (LES) computations by retaining the RANS characteristics in boundary layers while using the LES model away from walls. The hybrid approach embodied in the Detached Eddy Simulation (DES) methodology has been used with success in industrial flow simulations. However, it should be noted that the DES approach still requires LES-like mesh resolution away from walls. This is a simple consequence of the fact that the DES model defaults to LES at large distances from the walls. This may prove prohibitively expensive in simulations where large turbulent structures persists over most of the computational domain. In this work, a delayed two equation very large eddy simulation (VLES) model based on three length scales is introduced. The resolution control function used to rescale the Reynolds stresses is based on the ratio of the resolved to unresolved turbulence spectrum. The model constants are selected so that the Smagorinsky subgrid-scale model is recovered in the limit of grids approaching the resolution required for LES computations. The near wall RANS behaviour of the proposed model is obtained using blending functions. The objective was to implement this model using the open source library Caelus [2] and validate the results against two test cases involving turbulent vortex shedding from a bluff-body. The test cases used were flow past a square cylinder at a Reynolds number of 21,400 [3] and the Rudimentary Landing Gear benchmark case for Airframe Noise Computations (BANC) [4]. The numerical simulations were carried out using a transient solver based on the open source computational mechanics library Caelus. The pressure-based solver with second-order bounded spatial discretisation and second-order bounded implicit time marching scheme was applied to obtain a time-accurate solutions. Compressibility effects were negligible for the Mach numbers under consideration and the flow was treated as incompressible. Results from the simulations indicate close agreement between the proposed model and available experimental and numerical results. }, keywords = {Caelus, LES, RANS, Rudimentary Landing Gear, Square cylinder, Turbulence, VLES, Vortex shedding}, pubstate = {published}, tppubtype = {presentation} } 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 approaches [1] are currently used to offset the cost of Large Eddy Simulation (LES) computations by retaining the RANS characteristics in boundary layers while using the LES model away from walls. The hybrid approach embodied in the Detached Eddy Simulation (DES) methodology has been used with success in industrial flow simulations. However, it should be noted that the DES approach still requires LES-like mesh resolution away from walls. This is a simple consequence of the fact that the DES model defaults to LES at large distances from the walls. This may prove prohibitively expensive in simulations where large turbulent structures persists over most of the computational domain. In this work, a delayed two equation very large eddy simulation (VLES) model based on three length scales is introduced. The resolution control function used to rescale the Reynolds stresses is based on the ratio of the resolved to unresolved turbulence spectrum. The model constants are selected so that the Smagorinsky subgrid-scale model is recovered in the limit of grids approaching the resolution required for LES computations. The near wall RANS behaviour of the proposed model is obtained using blending functions. The objective was to implement this model using the open source library Caelus [2] and validate the results against two test cases involving turbulent vortex shedding from a bluff-body. The test cases used were flow past a square cylinder at a Reynolds number of 21,400 [3] and the Rudimentary Landing Gear benchmark case for Airframe Noise Computations (BANC) [4]. The numerical simulations were carried out using a transient solver based on the open source computational mechanics library Caelus. The pressure-based solver with second-order bounded spatial discretisation and second-order bounded implicit time marching scheme was applied to obtain a time-accurate solutions. Compressibility effects were negligible for the Mach numbers under consideration and the flow was treated as incompressible. Results from the simulations indicate close agreement between the proposed model and available experimental and numerical results. |

Velez, Carlos; Martin, Scott; Jemcov, Aleksandar; Vasu, Subith LES Simulation of an Enclosed Turbulent Reacting Methane Jet With the Tabulated Premixed CMC Method Conference ASME Turbo Expo 2015: Turbine Technical Conference and Exposition, Montreal, Quebec, Canada, June 15–19, 2015, ASME, 2015, ISBN: 978-0-7918-5669-7. Abstract | Links | BibTeX | Tags: Ceramic matrix composites, Methane, Simulation, Turbulence @conference{Velez2015, title = {LES Simulation of an Enclosed Turbulent Reacting Methane Jet With the Tabulated Premixed CMC Method}, author = {Carlos Velez and Scott Martin and Aleksandar Jemcov and Subith Vasu}, doi = {doi:10.1115/GT2015-43788}, isbn = {978-0-7918-5669-7}, year = {2015}, date = {2015-06-15}, booktitle = {ASME Turbo Expo 2015: Turbine Technical Conference and Exposition, Montreal, Quebec, Canada, June 15–19, 2015}, publisher = {ASME}, abstract = {The Tabulated Premixed Conditional Moment Closure Method (T-PCMC) has been shown to provide the capability to model turbulent, premixed methane flames with detailed chemistry and reasonable runtimes in a RANS environment [1]. Here the premixed conditional moment closure method is extended to Large Eddy Simulation. The new model is validated with the turbulent, enclosed reacting methane backward facing step data from El Banhawy [2]. The experimental data has a rectangular test section at atmospheric pressure and temperature with an inlet velocity of 10.5 m/s and an equivalence ratio of 0.9 for two different step heights. Contours of major species, velocity and temperature are provided. The T-PCMC model falls into the class of table lookup turbulent combustion models where the combustion model is solved offline over a range of conditions and stored in a table that is accessed by the CFD code using three controlling variables; the reaction progress variable, variance and local scalar dissipation rate. The local scalar dissipation is used to account for the affects of the small scale mixing on the reaction rates. A presumed shape beta function PDF is used to account for the effects of large scale turbulence on the reactions. Sub-grid scale models are incorporated for the scalar dissipation and variance. The open source CFD code OpenFOAM is used with the compressible Smagorinsky LES model. Velocity, temperature and major species are compared to the experimental data. Once validated, this “low runtime” CFD turbulent combustion model will have great utility for designing the next generation of lean premixed gas turbine combustors.}, keywords = {Ceramic matrix composites, Methane, Simulation, Turbulence}, pubstate = {published}, tppubtype = {conference} } The Tabulated Premixed Conditional Moment Closure Method (T-PCMC) has been shown to provide the capability to model turbulent, premixed methane flames with detailed chemistry and reasonable runtimes in a RANS environment [1]. Here the premixed conditional moment closure method is extended to Large Eddy Simulation. The new model is validated with the turbulent, enclosed reacting methane backward facing step data from El Banhawy [2]. The experimental data has a rectangular test section at atmospheric pressure and temperature with an inlet velocity of 10.5 m/s and an equivalence ratio of 0.9 for two different step heights. Contours of major species, velocity and temperature are provided. The T-PCMC model falls into the class of table lookup turbulent combustion models where the combustion model is solved offline over a range of conditions and stored in a table that is accessed by the CFD code using three controlling variables; the reaction progress variable, variance and local scalar dissipation rate. The local scalar dissipation is used to account for the affects of the small scale mixing on the reaction rates. A presumed shape beta function PDF is used to account for the effects of large scale turbulence on the reactions. Sub-grid scale models are incorporated for the scalar dissipation and variance. The open source CFD code OpenFOAM is used with the compressible Smagorinsky LES model. Velocity, temperature and major species are compared to the experimental data. Once validated, this “low runtime” CFD turbulent combustion model will have great utility for designing the next generation of lean premixed gas turbine combustors. |

## 2013 |

Martin, Scott; Jemcov, Aleksandar; de Ruijter, Bj"orn Modeling an Enclosed, Turbulent Reacting Methane Jet With the Premixed Conditional Moment Closure Method Inproceedings ASME Turbo Expo 2013: Turbine Technical Conference and Exposition, pp. V01BT04A011–V01BT04A011, American Society of Mechanical Engineers 2013. Abstract | Links | BibTeX | Tags: CMC, Methane, Mixing, Modelling, OpenFOAM, Turbulence @inproceedings{martin2013modeling, title = {Modeling an Enclosed, Turbulent Reacting Methane Jet With the Premixed Conditional Moment Closure Method}, author = { Scott Martin and Aleksandar Jemcov and Bj"orn de Ruijter}, doi = {10.1115/GT2013-95092}, year = {2013}, date = {2013-01-01}, booktitle = {ASME Turbo Expo 2013: Turbine Technical Conference and Exposition}, pages = {V01BT04A011--V01BT04A011}, organization = {American Society of Mechanical Engineers}, abstract = {Here the premixed Conditional Moment Closure (CMC) method is used to model the recent PIV and Raman turbulent, enclosed reacting methane jet data from DLR Stuttgart [1]. The experimental data has a rectangular test section at atmospheric pressure and temperature with a single inlet jet. A jet velocity of 90 m/s is used with an adiabatic flame temperature of 2,064 K. Contours of major species, temperature and velocities along with velocity rms values are provided. The conditional moment closure model has been shown to provide the capability to model turbulent, premixed methane flames with detailed chemistry and reasonable runtimes [2]. The simplified CMC model used here falls into the class of table lookup turbulent combustion models where the chemical kinetics are solved offline over a range of conditions and stored in a table that is accessed by the CFD code. Most table lookup models are based on the laminar 1-D flamelet equations, which assume the small scale turbulence does not affect the reaction rates, only the large scale turbulence has an effect on the reaction rates. The CMC model is derived from first principles to account for the effects of small scale turbulence on the reaction rates, as well as the effects of the large scale mixing, making it more versatile than other models. This is accomplished by conditioning the scalars with the reaction progress variable. By conditioning the scalars and accounting for the small scale mixing, the effects of turbulent fluctuations of the temperature on the reaction rates are more accurately modeled. The scalar dissipation is used to account for the effects of the small scale mixing on the reaction rates. The original premixed CMC model used a constant value of scalar dissipation, here the scalar dissipation is conditioned by the reaction progress variable. The steady RANS 3-D version of the open source CFD code OpenFOAM is used. Velocity, temperature and species are compared to the experimental data. Once validated, this CFD turbulent combustion model will have great utility for designing lean premixed gas turbine combustors.}, keywords = {CMC, Methane, Mixing, Modelling, OpenFOAM, Turbulence}, pubstate = {published}, tppubtype = {inproceedings} } Here the premixed Conditional Moment Closure (CMC) method is used to model the recent PIV and Raman turbulent, enclosed reacting methane jet data from DLR Stuttgart [1]. The experimental data has a rectangular test section at atmospheric pressure and temperature with a single inlet jet. A jet velocity of 90 m/s is used with an adiabatic flame temperature of 2,064 K. Contours of major species, temperature and velocities along with velocity rms values are provided. The conditional moment closure model has been shown to provide the capability to model turbulent, premixed methane flames with detailed chemistry and reasonable runtimes [2]. The simplified CMC model used here falls into the class of table lookup turbulent combustion models where the chemical kinetics are solved offline over a range of conditions and stored in a table that is accessed by the CFD code. Most table lookup models are based on the laminar 1-D flamelet equations, which assume the small scale turbulence does not affect the reaction rates, only the large scale turbulence has an effect on the reaction rates. The CMC model is derived from first principles to account for the effects of small scale turbulence on the reaction rates, as well as the effects of the large scale mixing, making it more versatile than other models. This is accomplished by conditioning the scalars with the reaction progress variable. By conditioning the scalars and accounting for the small scale mixing, the effects of turbulent fluctuations of the temperature on the reaction rates are more accurately modeled. The scalar dissipation is used to account for the effects of the small scale mixing on the reaction rates. The original premixed CMC model used a constant value of scalar dissipation, here the scalar dissipation is conditioned by the reaction progress variable. The steady RANS 3-D version of the open source CFD code OpenFOAM is used. Velocity, temperature and species are compared to the experimental data. Once validated, this CFD turbulent combustion model will have great utility for designing lean premixed gas turbine combustors. |

## 2009 |

Mohanarangam, Krishna; Nguyen, Tuan V; Stephens, Darrin W Evaluation of two equation turbulence models in a laboratory-scale thickener feedwell Conference Seventh International Conference on CFD in the Minerals and Process Industries, 2009. Abstract | Links | BibTeX | Tags: Feedwell, Model, Models, SST, Turbulence @conference{mohanarangam2009evaluation, title = {Evaluation of two equation turbulence models in a laboratory-scale thickener feedwell}, author = {Krishna Mohanarangam and Tuan V Nguyen and Darrin W Stephens}, doi = {10.13140/RG.2.1.1933.0407}, year = {2009}, date = {2009-01-01}, booktitle = {Seventh International Conference on CFD in the Minerals and Process Industries}, journal = {Seventh International Conference on Computational Fluid Dynamics in the Minerals and Process Industries}, pages = {9--11}, abstract = {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 to test the effectiveness of using tetrahedral/prism meshes in thickener feedwell geometries. Experimental results from a previously published lab-scale thickener feedwell geometry has been compared against the numerical predictions to verify the accuracy of these meshes towards replicating the flow structure. Mesh independency studies were also carried with these tetrahedral/prism meshes. The second objective is to test the suitability of four currently available two-equation turbulence models in our thickener feedwell geometry and their resulting flow structure. These turbulence models have been tested for open feedwell geometries with and without a shelf. NOMENCLATURE 1 a SST k-ω turbulence model constant B body forces c r1-3 curvature correction constant scale C curvature correction constant C ε1-2 k-ε turbulence model constant C μ k-ε turbulence model constant D rate of deformation 1 F First SST blending function 2 F Second SST blending function r f modified streamline curvature strength rotation f streamline curvature strength k turbulence kinetic energy k P shear production of turbulence kb P buoyancy production of turbulence p pressure p ' modified pressure * r curvature correction function r% curvature correction function S strain rate t time U velocity 3 α SST k-ω turbulence model constant β ′ SST k-ω turbulence model constant 3 β SST k-ω turbulence model constant ε turbulence dissipation rate μ dynamic viscosity eff μ effective viscosity t μ turbulent viscosity ρ density k σ k-ε turbulence model constant 3 k σ SST k-ω turbulence model constant ε σ k-ε turbulence model constant 2 ω σ SST k-ω turbulence model constant 3 ω σ SST k-ω turbulence model constant t υ kinematic turbulent viscosity Ω vorticity ω turbulence frequency Subscripts i, j, k velocity components INTRODUCTION Thickeners, as the name dictates, are used to concentrate fine particles from a slurry feed. Thickeners usually consist of a cylindrical feedwell surrounded concentrically by a large tank which forms the main body of the thickener. Slurry is fed into the feedwell along with a flocculant to induce the aggregation process under the turbulent conditions within the feedwell. Aggregates settle under gravity to produce a clear liquor collected from the outer edge of the upper surface of the thickener (overflow) and a concentrated underflow suspension of solids at the bottom of the tank. A slowly rotating rake is usually positioned at the base of the thickener to help move sediment out of the thickener for disposal or further processing. Industrial thickeners may be up to 100m in diameter, with feedwells up to 15m. The feedwell is core to the overall operational performance of a thickener. Feedwell use as a flocculation reactor is a relatively recent innovation, with the introduction of synthetic polymer flocculants in the 1960s. Feedwells also aid in dissipating the kinetic energy of the feed stream, helping to achieve uniform settling with minimum turbulence, and thereby reducing/eliminating short-circuiting in the thickener.}, keywords = {Feedwell, Model, Models, SST, Turbulence}, pubstate = {published}, tppubtype = {conference} } 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 to test the effectiveness of using tetrahedral/prism meshes in thickener feedwell geometries. Experimental results from a previously published lab-scale thickener feedwell geometry has been compared against the numerical predictions to verify the accuracy of these meshes towards replicating the flow structure. Mesh independency studies were also carried with these tetrahedral/prism meshes. The second objective is to test the suitability of four currently available two-equation turbulence models in our thickener feedwell geometry and their resulting flow structure. These turbulence models have been tested for open feedwell geometries with and without a shelf. NOMENCLATURE 1 a SST k-ω turbulence model constant B body forces c r1-3 curvature correction constant scale C curvature correction constant C ε1-2 k-ε turbulence model constant C μ k-ε turbulence model constant D rate of deformation 1 F First SST blending function 2 F Second SST blending function r f modified streamline curvature strength rotation f streamline curvature strength k turbulence kinetic energy k P shear production of turbulence kb P buoyancy production of turbulence p pressure p ' modified pressure * r curvature correction function r% curvature correction function S strain rate t time U velocity 3 α SST k-ω turbulence model constant β ′ SST k-ω turbulence model constant 3 β SST k-ω turbulence model constant ε turbulence dissipation rate μ dynamic viscosity eff μ effective viscosity t μ turbulent viscosity ρ density k σ k-ε turbulence model constant 3 k σ SST k-ω turbulence model constant ε σ k-ε turbulence model constant 2 ω σ SST k-ω turbulence model constant 3 ω σ SST k-ω turbulence model constant t υ kinematic turbulent viscosity Ω vorticity ω turbulence frequency Subscripts i, j, k velocity components INTRODUCTION Thickeners, as the name dictates, are used to concentrate fine particles from a slurry feed. Thickeners usually consist of a cylindrical feedwell surrounded concentrically by a large tank which forms the main body of the thickener. Slurry is fed into the feedwell along with a flocculant to induce the aggregation process under the turbulent conditions within the feedwell. Aggregates settle under gravity to produce a clear liquor collected from the outer edge of the upper surface of the thickener (overflow) and a concentrated underflow suspension of solids at the bottom of the tank. A slowly rotating rake is usually positioned at the base of the thickener to help move sediment out of the thickener for disposal or further processing. Industrial thickeners may be up to 100m in diameter, with feedwells up to 15m. The feedwell is core to the overall operational performance of a thickener. Feedwell use as a flocculation reactor is a relatively recent innovation, with the introduction of synthetic polymer flocculants in the 1960s. Feedwells also aid in dissipating the kinetic energy of the feed stream, helping to achieve uniform settling with minimum turbulence, and thereby reducing/eliminating short-circuiting in the thickener. |