# Publications

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## 2015 |

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. |

Kelly, Ryan; Jemcov, Aleksandar; Rennie, Mark R; Wang, Kan; Jumper, Meng Wang5and Eric J; Whitely, Matthew R; Goorskey, David Computation of the Aero-Optical Effect of a Helicopter Rotor Wake Using Unsteady RANS and LES Conference 53rd AIAA Aerospace Sciences Meeting, 2015. Abstract | Links | BibTeX | Tags: Computation, LES, RANS @conference{kellycomputation, title = {Computation of the Aero-Optical Effect of a Helicopter Rotor Wake Using Unsteady RANS and LES}, author = { Ryan Kelly and Aleksandar Jemcov and R Mark Rennie and Kan Wang and Meng Wang5and Eric J Jumper and Matthew R Whitely and David Goorskey}, doi = {doi:10.2514/6.2015-0678}, year = {2015}, date = {2015-01-02}, booktitle = {53rd AIAA Aerospace Sciences Meeting}, abstract = {The aero-optical characteristics of the wake beneath a hovering helicopter was computed using Unsteady RANS (URANS) and Large-Eddy Simulations (LES). The computational methodology consisted of combining a URANS simulation with a vorticity-confinement method to produce a model of the large-scale vortex wake of the helicopter. An LES simulation of the local flow around a vortex segment was then performed and the solutions were superimposed onto the large-scale vortex structures computed using the URANS CFD, and time-resolved optical wavefronts were computed on a beam of light passing through the flow. The computed optical aberrations of the wake can be used to develop adaptive-optic systems or other beam-control approaches.}, keywords = {Computation, LES, RANS}, pubstate = {published}, tppubtype = {conference} } The aero-optical characteristics of the wake beneath a hovering helicopter was computed using Unsteady RANS (URANS) and Large-Eddy Simulations (LES). The computational methodology consisted of combining a URANS simulation with a vorticity-confinement method to produce a model of the large-scale vortex wake of the helicopter. An LES simulation of the local flow around a vortex segment was then performed and the solutions were superimposed onto the large-scale vortex structures computed using the URANS CFD, and time-resolved optical wavefronts were computed on a beam of light passing through the flow. The computed optical aberrations of the wake can be used to develop adaptive-optic systems or other beam-control approaches. |

## 2013 |

Morris, Scott; Perez, Ethan; Cameron, Joshua; Jemcov, Aleksandar Entropy Generation in Three-dimensional, Swirling Flows Inproceedings APS Meeting Abstracts, pp. 27003, 2013. Abstract | BibTeX | Tags: Entropy, RANS, Swirling flow @inproceedings{morris2013entropy, title = {Entropy Generation in Three-dimensional, Swirling Flows}, author = { Scott Morris and Ethan Perez and Joshua Cameron and Aleksandar Jemcov}, year = {2013}, date = {2013-01-01}, booktitle = {APS Meeting Abstracts}, volume = {1}, pages = {27003}, abstract = {Entropy generation in a transonic, highly loaded, axial turbine stage has been investigated via application of the entropy transport equation. The use of a RANS simulation required additional consideration of entropy transport associated with the time-averaging of products of fluctuating quantities. Analysis of the RANS entropy transport equation allowed the investigators to calculate the volumetric distribution of D ̲ s ̲ / Dt ̲ that is, the time rate of change of mean entropy of a material particle. The quantity D ̲ s ̲ / Dt ̲ revealed localized regions of entropy increases and decreases of material particles. It was discovered that regions of large + D ̲ s ̲ / Dt ̲ occur primarily on the blade suction surface. Additionally, it was found that the passage vortex core, typically associated with high entropy fluid, corresponded with regions of D ̲ s ̲ / Dt ̲ ~ 0 . This result suggests that entropy is generated on the blade suction surface and then collected and convected by the blade passage vortex.}, keywords = {Entropy, RANS, Swirling flow}, pubstate = {published}, tppubtype = {inproceedings} } Entropy generation in a transonic, highly loaded, axial turbine stage has been investigated via application of the entropy transport equation. The use of a RANS simulation required additional consideration of entropy transport associated with the time-averaging of products of fluctuating quantities. Analysis of the RANS entropy transport equation allowed the investigators to calculate the volumetric distribution of D ̲ s ̲ / Dt ̲ that is, the time rate of change of mean entropy of a material particle. The quantity D ̲ s ̲ / Dt ̲ revealed localized regions of entropy increases and decreases of material particles. It was discovered that regions of large + D ̲ s ̲ / Dt ̲ occur primarily on the blade suction surface. Additionally, it was found that the passage vortex core, typically associated with high entropy fluid, corresponded with regions of D ̲ s ̲ / Dt ̲ ~ 0 . This result suggests that entropy is generated on the blade suction surface and then collected and convected by the blade passage vortex. |