# Publications

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## 2015 |

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. |

## 2012 |

Jemcov, Aleksandar; Williams, Theodore; Corke, Thomas Comparative Study of Reynolds Averaged and Embedded Large Eddy Simulations of a High Pressure Turbine Stage Journal Article Bulletin of the American Physical Society, 57 , 2012. Abstract | BibTeX | Tags: ELES, Flowfield, LES, RAS, Simulation @article{jemcov2012comparative, title = {Comparative Study of Reynolds Averaged and Embedded Large Eddy Simulations of a High Pressure Turbine Stage}, author = { Aleksandar Jemcov and Theodore Williams and Thomas Corke}, year = {2012}, date = {2012-01-01}, journal = {Bulletin of the American Physical Society}, volume = {57}, publisher = {APS}, abstract = {An Embedded Large Eddy Simulation (ELES) approach is used to simulate the flow path through a high pressure turbine stage. The turbine stage includes the entry duct, stationary inlet and exit guide vanes, and a rotor. The rotor blade design includes a squealer tip. The flowfield around the rotor is simulated using LES. A Reynolds Averaged Simulation (RAS) is used to simulate the rest of the flow domain. The interface between RAS and LES domains uses the RAS turbulence quantities as a means of obtaining length scales that are used in computing the vorticity that is required to trigger a proper energy cascade within the LES part of the flow field. The ELES approach allows for substantial computational savings since it allows for different mesh resolutions in various parts of the computational domain as needed. The objective of this work is to observe at a lower computational cost, the local flow features that cannot be resolved in a RAS approach. A comparative analysis between RAS and ELES approaches for this turbomachinery problem is then presented.}, keywords = {ELES, Flowfield, LES, RAS, Simulation}, pubstate = {published}, tppubtype = {article} } An Embedded Large Eddy Simulation (ELES) approach is used to simulate the flow path through a high pressure turbine stage. The turbine stage includes the entry duct, stationary inlet and exit guide vanes, and a rotor. The rotor blade design includes a squealer tip. The flowfield around the rotor is simulated using LES. A Reynolds Averaged Simulation (RAS) is used to simulate the rest of the flow domain. The interface between RAS and LES domains uses the RAS turbulence quantities as a means of obtaining length scales that are used in computing the vorticity that is required to trigger a proper energy cascade within the LES part of the flow field. The ELES approach allows for substantial computational savings since it allows for different mesh resolutions in various parts of the computational domain as needed. The objective of this work is to observe at a lower computational cost, the local flow features that cannot be resolved in a RAS approach. A comparative analysis between RAS and ELES approaches for this turbomachinery problem is then presented. |

## 2007 |

Morgans, Rick C; Doolan, Con J; Stephens, Darrin W Derivative free global optimisation of CFD simulations Conference 16th Australasian Fluid Mechanics Conference, 2007. Abstract | BibTeX | Tags: Algorithm, EGO, OpenFOAM, Simulation @conference{morgans2007derivative, title = {Derivative free global optimisation of CFD simulations}, author = {Rick C Morgans and Con J Doolan and Darrin W Stephens}, year = {2007}, date = {2007-01-01}, booktitle = {16th Australasian Fluid Mechanics Conference}, abstract = {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 robust computational tool, with the contraction shape defined by a two parameter B´ezier curve. The second application is a simplified test case with a known minimum calculated using a commercial CFD code. For the optimisation of complex CFD simulations, it is sometimes advantageous to use an efficient derivative free global optimisation algorithm because of potentially long simulation times, the objective function may contain multiple local minima and it is often difficult to evaluate analytical or numerical gradients. The Efficient Global Optimisation (EGO) algorithm sequentially samples results from an expensive calculation, does not require derivative information, uses an inexpensive surrogate to search for a global optimum, and is used in this current work. For both applications, the EGO algorithm is able to efficiently and robustly find a global optimum that satisfies any constraints.}, keywords = {Algorithm, EGO, OpenFOAM, Simulation}, pubstate = {published}, tppubtype = {conference} } 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 robust computational tool, with the contraction shape defined by a two parameter B´ezier curve. The second application is a simplified test case with a known minimum calculated using a commercial CFD code. For the optimisation of complex CFD simulations, it is sometimes advantageous to use an efficient derivative free global optimisation algorithm because of potentially long simulation times, the objective function may contain multiple local minima and it is often difficult to evaluate analytical or numerical gradients. The Efficient Global Optimisation (EGO) algorithm sequentially samples results from an expensive calculation, does not require derivative information, uses an inexpensive surrogate to search for a global optimum, and is used in this current work. For both applications, the EGO algorithm is able to efficiently and robustly find a global optimum that satisfies any constraints. |

Jasak, Hrvoje; Jemcov, Aleksandar; Maruszewski, Joseph P Preconditioned linear solvers for large eddy simulation Conference CFD 2007 Conference, CFD Society of Canada, 2007. Abstract | BibTeX | Tags: Algebraic Multi-grid Solver, Linear Solver, Preconditioner, Simulation, Solver @conference{jasak2007preconditioned, title = {Preconditioned linear solvers for large eddy simulation}, author = { Hrvoje Jasak and Aleksandar Jemcov and Joseph P Maruszewski}, year = {2007}, date = {2007-01-01}, booktitle = {CFD 2007 Conference, CFD Society of Canada}, abstract = {Efficient solution of linear systems of equations stemming from cell centred Finite Volume Discretisation in Large Eddy Simulation is critical in large-scale simulations. This paper presents a class of sparse matrix iterative solvers combining Algebraic Multigrid (AMG) and Krylov Space techniques with the idea of combining residual reduction techniques to improve efficiency over the current solver technology. Emphasis is placed on choosing combinations of a solver, a preconditioner and a smoother and setting control parameters that yield the most efficient solution. Results show consistent superiority of AMG-preconditioned Conjugate Gradient solvers for matrices under consideration}, keywords = {Algebraic Multi-grid Solver, Linear Solver, Preconditioner, Simulation, Solver}, pubstate = {published}, tppubtype = {conference} } Efficient solution of linear systems of equations stemming from cell centred Finite Volume Discretisation in Large Eddy Simulation is critical in large-scale simulations. This paper presents a class of sparse matrix iterative solvers combining Algebraic Multigrid (AMG) and Krylov Space techniques with the idea of combining residual reduction techniques to improve efficiency over the current solver technology. Emphasis is placed on choosing combinations of a solver, a preconditioner and a smoother and setting control parameters that yield the most efficient solution. Results show consistent superiority of AMG-preconditioned Conjugate Gradient solvers for matrices under consideration |

## 2006 |

Rackemann, Darryn W; Broadfoot, Ross; Stephens, Darrin W Improved CFD modelling of natural circulation vacuum pans Inproceedings Australian Society of Sugar Cane Technologists, pp. 462, 2006. Abstract | Links | BibTeX | Tags: Circulation, Heat Transfer, Modelling, Performance, Simulation, Vacuum Pan, Validation @inproceedings{rackemann2006improved, title = {Improved CFD modelling of natural circulation vacuum pans}, author = {Darryn W Rackemann and Ross Broadfoot and Darrin W Stephens}, doi = {10.13140/RG.2.1.1867.5046}, year = {2006}, date = {2006-01-01}, booktitle = {Australian Society of Sugar Cane Technologists}, journal = {PROCEEDINGS-AUSTRALIAN SOCIETY OF SUGAR CANE TECHNOLOGISTS}, volume = {28}, pages = {462}, abstract = {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 captured in the SRI CFD model was previously too complicated for most CFD software. With improvements to the software, these complex physical processes can now be modelled, albeit a little cumbersomely. This paper details the development of CFD models to predict the circulation patterns and heat transfer occurring in natural circulation crystallisation vacuum pans. Model validation involved checking the circulation velocities predicted by the CFD model with circulation velocity data measured on factory pans. The predictions were in reasonable agreement with factory measurements. The validated CFD model was used to investigate the effect of altering key dimensions on batch pans and on two different continuous pan designs. The batch pan investigations included: • Increasing the volumetric region above the calandria by flaring the pan body; • Reducing the clearance underneath the calandria; and • Changing the dimensions of the tubes (tube diameter and length) while maintaining the same heat transfer area and keeping the evaporation rate constant. The effect of variations in pan geometry, massecuite viscosity and operating level above the calandria were considered for the batch pan simulations. These results provide interesting insight into the complicated processes involved in the operation of natural circulation vacuum pans.}, keywords = {Circulation, Heat Transfer, Modelling, Performance, Simulation, Vacuum Pan, Validation}, pubstate = {published}, tppubtype = {inproceedings} } 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 captured in the SRI CFD model was previously too complicated for most CFD software. With improvements to the software, these complex physical processes can now be modelled, albeit a little cumbersomely. This paper details the development of CFD models to predict the circulation patterns and heat transfer occurring in natural circulation crystallisation vacuum pans. Model validation involved checking the circulation velocities predicted by the CFD model with circulation velocity data measured on factory pans. The predictions were in reasonable agreement with factory measurements. The validated CFD model was used to investigate the effect of altering key dimensions on batch pans and on two different continuous pan designs. The batch pan investigations included: • Increasing the volumetric region above the calandria by flaring the pan body; • Reducing the clearance underneath the calandria; and • Changing the dimensions of the tubes (tube diameter and length) while maintaining the same heat transfer area and keeping the evaporation rate constant. The effect of variations in pan geometry, massecuite viscosity and operating level above the calandria were considered for the batch pan simulations. These results provide interesting insight into the complicated processes involved in the operation of natural circulation vacuum pans. |