| 1. |
- Andric, Jelena, 1979
(författare)
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A computational parametric analysis of cavitating flows in injector nozzles
- 2017
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Ingår i: International Journal of Modelling and Simulation. - : Informa UK Limited. - 0228-6203 .- 1925-7082. ; 37:4, s. 220-226
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Tidskriftsartikel (refereegranskat)abstract
- The fuel injection system in diesel engines has crucial influence on the engine’s combustion process and emission formation. Cavitation in injector nozzles plays a critical role in primary spray break-up and atomization. Understanding the phenomenon of cavitation is hence important for accurate design of the injection process. This work presents a computational study of the characteristics of cavitating flows in the two-dimensional (2D) injector nozzle. The computations are performed by employing the multi-phase mixture approach with the k–ε realizable turbulence model and Schnerr–Sauer cavitation model. The results demonstrate the capability of the modeling framework to successfully predict the following experimentally observed cavitation regimes: no cavitation, developing cavitation, and super cavitation. A parametric study of the effects of the cavitation number σ and the Reynolds number Re verifies the experimental finding that cavitation strongly depends on σ, while the effect of Re is not large.
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| 2. |
- Andric, Jelena, 1979, et al.
(författare)
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A computational study of the impacts of driving aggressiveness on fuel consumption sensitivity in a parallel HEV
- 2017
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Ingår i: The 7th International Conference & Workshop REMOO–2017, 10-12 May 2017, Venice, Italy. - 9783981827552
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Konferensbidrag (refereegranskat)abstract
- Hybrid electric vehicles (HEVs) have an advantage over their conventional counterparts interms of reducing fuel consumption and meeting increasingly stringent emission reductioncriteria. Nonetheless, the variation in fuel consumption due to differences in driving style andbehaviour under real-world driving conditions is greater in HEVs than in the conventionalones. A reduction in variability of fuel consumption is hence of compelling relevance for designand optimization of HEVs. This work employs vehicle powertrain simulations to analyze theeffects of driving style on fuel consumption sensitivity in parallel HEVs for a range of trafficconditions. The driving aggressiveness is modeled using velocity-scaling and acceleration-scalingmethods, respectively, to account for various velocity characteristics and accelerationlevels. Hybrid powertrain simulations assess and quantify the impacts of the engineperformance, as well as the significance of the energy recovered by regenerative braking. Theresults presented in this paper provide valuable inputs for optimal control of HEVs to meetcustomer driving needs and expectations.
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| 3. |
- Andric, Jelena, 1979, et al.
(författare)
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A particle-level rigid fiber model for high-Reynolds number flow, implemented in a general-purpose CFD code
- 2013
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Ingår i: 8th International Conference on Multiphase Flow ICMF 2013, Korea.
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Konferensbidrag (refereegranskat)abstract
- A particle-level rigid fiber model has been integrated into a general-purpose, open source computational fluid dynamics code to carry out detailed studies of fiber–flow interactions in realistic flow fields. The fibers are modeled as chains of cylindrical segments, and their translational and rotational degrees of freedom are considered. The equations of motion contain the contributions from hydrodynamic forces and torques, and the segment inertia is taken into account. The model is validated for the rotational motion of isolated fibers in simple shear flow, and the computed period of rotation is in good agreement with the one computed using Jeffery’s equation for a prolate spheroid with an equivalent aspect ratio. The model is applied by suspending a number of fibers in the swirling flow of a conical diffuser, resembling one stage in the dry-forming of pulp mats. The Reynolds-averaged Navier–Stokes equations with an eddy-viscosity turbulence model are employed to describe the fluid motion, and a one-way coupling between the fibers and the fluid phase is included. The dependence of the fiber motion on initial position and density is analyzed.
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| 4. |
- Andric, Jelena, 1979, et al.
(författare)
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A study of a flexible fiber model and its behavior in DNS of turbulent channel flow
- 2013
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Ingår i: Acta Mechanica. - : Springer Science and Business Media LLC. - 0001-5970 .- 1619-6937. ; 224:10, s. 2359-2374
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of individual flexible fibers in a turbulent flow field have been analyzed, varying their initial position, density and length. A particlelevel fiber model has been integrated into a general-purpose, open source Computational Fluid Dynamics (CFD) code. The fibers are modeled as chains of cylindrical segments connected by ball and socket joints. The equations of motion of the fibers contain the inertia of the segments, the contributions from hydrodynamic forces and torques, and the connectivity forces at the joints. Direct Numerical Simulation (DNS) of the incompressible Navier–Stokes equations is used to describe the fluid flow in a plane channel and a one-way coupling is considered between the fibers and the fluid phase. We investigate the translational motion of fibers by considering the mean square displacement of their trajectories. We find that the fiber motion is primarily governed by velocity correlations of the flow fluctuations. In addition, we show that there is a clear tendency of the thread-like fibers to evolve into complex geometrical configurations in a turbulent flow field, in fashion similar to random conformations of polymer strands subjected to thermal fluctuations in a suspension. Finally, we show that fiber inertia has a significant impact on reorientation time-scales of fibers suspended in a turbulent flow field.
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| 5. |
- Andric, Jelena, 1979, et al.
(författare)
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Ballistic deflection of fibres in decelerating flow
- 2016
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Ingår i: International Journal of Multiphase Flow. - : Elsevier BV. - 0301-9322 .- 1879-3533. ; 85, s. 57-66
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the motion of inertial, rod-like fibres in the decelerating flow of a wedge-shaped channel with non-creeping fibre-flow interactions. We consider the trajectories of isolated fibres to identify the conditions for which these trajectories deflect from the streamlines of the flow as well as a rectilinear path. We carry out analytical and numerical studies under the assumption of an infinite fibre hydrodynamic resistance to transverse flow, and we expand the numerical study by taking into account a finite transverse hydrodynamic resistance. The analytical analysis identifies a longitudinal ballistic number Bℓ and a transverse ballistic number Bt as two dimensionless parameters that govern the fibre dynamics. It is found that Bℓ is the product of the Stokes number Stℓ in the longitudinal direction of the fibre and the channel opening angle β. As anticipated, a fibre moves along the streamlines in the viscosity-dominated regime (Bℓ « 1, Bt « 1), while it moves in a straight line without being rotated in the inertia-dominated regime (Bt » 1). The focus of the present study is on the intermediate regime (Bℓ » 1, Bt
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| 6. |
- Andric, Jelena, 1979, et al.
(författare)
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Calibration Procedure for Measurement-Based Fast Running Model for Hardware-in-the-Loop Powertrain Systems
- 2020
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 2020- April:April
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Tidskriftsartikel (refereegranskat)abstract
- The requirements set for the next-generation powertrain systems (e.g. performance and emissions) are becoming increasingly stringent with ever-shortening time-to-markets at reduced costs. To remain competitive automotive companies are progressively relying on model-driven development and virtual testing. Virtual test benches, such as Hardware-in the-Loop simulators, are powerful tools to reduce the amount of physical testing and speed up engine software calibration process. The introduction of these technologies places new, often conflicting demands (such as higher predictability, faster simulation speed, and reduced calibration effort ) upon simulation models used at Hardware-in-the-Loop test benches. The new models are also expected to offer compliance to industry standards, performance and usability to further increase the usage of virtual tests in powertrain development. The present work describes a novel verification process for creating a fast running model for a heavy-duty diesel engine using FRM-d Builder in GT-SUITE simulation software. The approach uniquely applies the combination physical modelling and parameter estimation techniques, while relying solely on test cell measurements without data maps from the manufactures (e.g. for turbine and compressor). The procedure provides detailed description for subsystem calibration for turbocharger and intake path. The developed model is successfully employed at the VIRTEC system in Volvo Penta. The simulation results for engine performance and exhaust emissions provide favourable results for both steady-state and transient operating conditions.
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| 7. |
- Andric, Jelena, 1979, et al.
(författare)
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Description and validation of a flexible fiber model, implemented in a general-purpose CFD code
- 2013
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Ingår i: Proceedings of the 8th International Conference on Multiphase Flow ICMF 2013, Korea.
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Konferensbidrag (refereegranskat)abstract
- A flexible fiber model has been implemented in a general purpose open-source computational fluid dynamics code. The fibers are modeled as chains of cylindrical segments. Each segment is tracked individually and their equations of motion account for the hydrodynamic forces and torques from the interaction with the fluid, the elastic bending and twisting torques, and the connectivity forces and moments that ensure the fiber integrity. The segment inertia is taken into account and a one-way coupling with the fluid phase is considered. The model is applied to the rotational motion of an isolated fiber in a low segment Reynolds number shear flow. In the case of a stiff fiber, the computed period of rotation is in good agreement with the one computed using Jeffery's equation for an equivalent spheroid aspect ratio. A qualitative comparison is made with experimental data for flexible fibers. These results show that the implemented model can reproduce the known dynamical behavior of rigid and flexible fibers successfully.
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| 8. |
- Andric, Jelena, 1979, et al.
(författare)
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Development and Calibration of One Dimensional Engine Model for Hardware-in-the-Loop Applications
- 2018
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 2018-April
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Tidskriftsartikel (refereegranskat)abstract
- The present paper aims at developing an innovative procedure to create a one-dimensional (1D) real-time capable simulation model for a heavy-duty diesel engine. The novelty of this approach is the use of the top-level engine configuration, test cell measurement data, and manufacturer maps as opposite to common practice of utilizing a detailed 1D engine model. The objective is to facilitate effective model adjustments and hence further increase the application of Hardware-in-the-Loop (HiL) simulations in powertrain development. This work describes the development of Fast Running Model (FRM) in GT-SUITE simulation software. The cylinder and gas-path modeling and calibration are described in detail. The results for engine performance and exhaust emissions produced satisfactory agreement with both steady-state and transient experimental data. Therefore, the presented methodology shows a great potential for testing and validation of new control strategies in Engine Management System (EMS) and for optimizing engine performance using HiL systems. The model has been successfully used in powertrain testing and calibration in the VIRtual TEst Cell (VIRTEC) system at Volvo Penta.
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| 9. |
- Andric, Jelena, 1979
(författare)
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Implementation of a flexible fiber model in a general purpose CFD code
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work is related to the process of making pulp mats for use in hygienicproducts. One part of that process is the transportation of flexiblecellulose fibers suspended in flowing air. The fibers should be evenlydistributed on the substrate, and it is thus of high importance to avoidthe formation of fiber flocks during the transportation. The purposeof the present work is to implement a flexible fiber model in a generalpurpose Computational Fluid Dynamics (CFD) code, for detailed studiesof fiber-fiber and fiber-flow interaction in real flow situations. Thefibers are modeled as chains of cylindrical segments, and the translationaland rotational degrees of freedom of each segment are taken intoaccount. Each segment is tracked individually, using Lagrangian ParticleTracking (LPT), and the equations of fibermotion are derived fromthe conservation of momentum for each segment. The segment inertiais taken into account and the one-way coupling with the fluid phase isconsidered. The fiber integrity is ensured through connectivity forcesacting between the adjacent fiber segments. The implemented modelhas been applied both with imposed flow fields, and in a flow field simultaneouslypredicted by the CFD solver. The results show that thefibers are transported by the flow and are deformed due to flow gradients.Further, a generic test case is described and used to validate theenergy conservation and response time of the fiber model concept.This work is the foundation for further improvements of the fibermodelthrough the addition of bending and twisting forces, as well as the inclusionof interaction (e.g. collision) forces between individual fiber segments.These features, together with a two-way coupling with the flow,will lead to a more complete fiber model.
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| 10. |
- Andric, Jelena, 1979, et al.
(författare)
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Numerical investigation of fiber flocculation in the air flow of an asymmetric diffuser
- 2014
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Ingår i: Proceedings of the ASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting and 12th International Conference on Nanochannels, Microchannels and Minichannels, FEDSM 201, August 3-7, Chicago, Illinois, USA..
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Konferensbidrag (refereegranskat)abstract
- A particle-level rigid fiber model is used to studyflocculation in an asymmetric planar diffuser with a turbulent Newtonian fluid flow, resembling one stage in dry-forming process of pulp mats. The fibers are modeled as chains of rigid cylindrical segments. The equations of motion incorporatehydrodynamic forces and torques from the interaction with thefluid, and the fiber inertia is taken into account. The flow isgoverned by the Reynolds-averaged Navier ̶ Stokes equationswith the standard k-omega turbulence model. A one-waycoupling between the fibers and the flow is considered. Astochastic model is employed for the flow fluctuations tocapture the fiber dispersion. The fibers are assumed to interactthrough short-range attractive forces, causing them to interlockas the fiber-fiber contacts occur during the flow. It is found thatthe formation of fiber flocs is driven by both the turbulenceinduceddispersion and the gradient of the averaged flow field
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