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| 2. |
- Abrahamsson, Hans, 1966, et al.
(författare)
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Turbulence in a Two-Dimensional Wall-Jet - Experiments and Modeling
- 1992
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Ingår i: 13th Turbulence Conference in Missouri-Rolla..
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Konferensbidrag (refereegranskat)abstract
- An experimental and numerical investigation of the turbulence field in a two-dimensional wall-jet has been carried out in a well-defined geometry. The measurements were performed using a hot-wire technique and the calculations were carried out with a standard k-ε model as well as an algebraic stress model (ASM), using elliptic solvers. For the mean velocity field, good agreements were found between the measurements and the calculations. The measurements of the turbulence intensities reveal two maxima in the stream-wise and span-wise components, while only one maximum was found in the normal component. Also in the shear stress two maxima were found. A comparison between calculations and measurements indicates that improved turbulence models are needed.
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| 3. |
- Abrahamsson, Hans, 1966, et al.
(författare)
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Turbulence Measurements in a Two-Dimensional Wall-Jet
- 1991
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Ingår i: Eight Turbulent Shear Flow Conference, München.
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Konferensbidrag (refereegranskat)abstract
- The high capacity of todays computers has enabled the extension of turbulence models to strongly anisotropic flow fields, i.e. the interest has been focused on the use of the models based on the transport equations for the Reynolds stresses (RST models). To improve these turbulence models well-defined, simple and fundamental experiments are needed, in which gradients of the different turbulence parameters are determined. Together with direct simulations of the Navier-Stokes equations these experiments yield a good base for the improvement of the modelling of different terms in the Reynolds equations. An excellent presentation of the closure problem and the terms of interest for the development of turbulence models has recently been published by Groth (1991). A fundamental, well-defined and simple flow case is the wall-jet, where an interaction between a wall boundary layer and a free shear layer forms the anisotropy as well as the inhomogeneous character of the flow field. A comprehensive literature survey of wall-jets was carried out already in the beginning of the eighties by Launder and Rodi (1980), who studied a large number of more or less well-defined wall-jet experiments. The main conclusion of this survey was a lack of well-defined experiments in simple and fundamental geometries. If the study is limited to the two-dimensional case, a further conclusion from the work of Launder and Rodi was that many of the studied flow cases did not fulfil the condition of two-dimensionality. Although more than ten years have passed since the work of Laundry and Rodi was presented, very few investigations have been reported in which fundamental wall-jets have been studied. Especially well-defined turbulence measurements are needed, since anisotropy of the two-dimensional wall-jet yields a case well suited for the evaluation of e.g. new dissipation models, see Hallbäck et al. (1990). The purpose of the present work was to determine the turbulence field of a two-dimensional wall-jet in a simple and also well-defined geometry without influence of an outer disturbing flow field. To accomplish these measurements was a wall-jet rig used. All turbulence measurements were carried out using hot-wire techniques, single- and cross wires. The measurements presented here were performed at a Reynolds number of ___, based on the slot height and the extensions of the measurements in the flow direction was in the range of x/h=25 through x/h=156 (x-coordinate in the main flow direction and h-slot height).
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| 4. |
- Andersson, Helge, 1950, et al.
(författare)
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Turbulence in the Vicinity of a Rotating Cylinder in a Quiescent Fluid
- 1991
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Ingår i: Eight Turbulence Shear Flow Conference, Munchen.
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Konferensbidrag (refereegranskat)abstract
- An experimental and numerical investigation of the turbulence field in the vicinity of a rotating cylinder in a quiescent fluid has been carried out. Radial distributions of mean velocity and non-vanishing Reynolds stress components have been measured using hot-wire technique, and corresponding components have been calculated with a low-Reynolds number second- moment closure model. From the measurements it can be concluded the turbulence field is established in the present set up at a Reynolds number which is roughly twenty times larger than earlier measurements have shown. Comparisons between calculations and measurements yield some deviations. However, a qualitatively good agreement is obtained. In the paper, different methods for the determination of the friction velocity are also described and discussed.
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| 5. |
- Aronson, Dag, 1959, et al.
(författare)
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An Estimate of the Pressure Strain, Rate Tensor in a Plane Cylinder Wake
- 1994
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Ingår i: Fifth European Turbulence Conference in Siena, Italy, July 5-8 1994.
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Konferensbidrag (refereegranskat)abstract
- The far wake of a cylinder has been studied in order to provide accurate experimental information on the normal component of the pressure-strain rate tensor by balancing the turbulent kinetic energy budget and Reynolds stress transport (RST) equations. A non-isotropic dissipation rate tensor was found, thus fulfilling the basic physical integral constraint of the diffusion and indicating an energy redistribution as described by the pressure-strain rate correlations.
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| 6. |
- Aronson, Dag, 1959, et al.
(författare)
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Measured and Modelled Component (11) of the Dissipation Rate Tensor
- 1992
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Ingår i: 13th Turbulence Conference in Missouri-Rolla, Missouri.
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Konferensbidrag (refereegranskat)abstract
- The anisotropy of the dissipation rate tensor has been studied in the self-preserving region of a cylinder wake. Hot-wire techniques have been employed to measure velocity derivatives in the stream-wise, lateral and normal direction. From these measurements the stream-wise diagonal component of the dissipation rate tensor was determined and compared to that predicted by an anisotropic dissipation model. It was found that the dissipation rate anisotropy could essentially be accounted for by the employed model. Triple velocity correlations were also measured and compared with corresponding profiles obtained from closure models.
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| 7. |
- Astaneh, Majid, 1990, et al.
(författare)
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Lithium-ion Battery Pack Design for Electric Vehicles Using GT-AutoLion: Multi-Physics Simulation and Multi-Criteria Optimization Approach
- 2021
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Ingår i: Global Gamma Technologies Virtual Conference.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- High specific energy battery systems with improved thermal performance are required for large-scale introduction of electric vehicles (EVs) into the market. This study presents a comprehensive multi-physics simulation and multi-criteria optimization framework for Lithium-ion (Li-ion) battery pack design for EV applications. The battery cells are modeled by electrochemical thermally coupled approach using GT-AutoLion. Multi-objective optimization using genetic algorithm is employed to explore energy and thermally efficient cell design alternatives. The performances of the optimally designed cells are then evaluated under pack environment to account for inhomogeneities in large traction battery packs under realistic working scenarios. It is observed that considering the thermal efficiency of battery cells is crucial for obtaining improved battery pack performance. The integrated framework developed in this work provides systematic pack-aware guidelines for manufacturers already at the initial cell design stage. Moreover, the proposed design optimization methodology is generic, handing over valuable knowledge for future cell and pack designs for various applications.
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| 8. |
- Astaneh, Majid, 1990, et al.
(författare)
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Lithium-Ion Battery Pack Modelling for Electric Vehicles in Mining Applications Using GT-AutoLion
- 2020
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Large traction battery packs play a pivotal role in electric vehicles (EVs) to fulfill the system demand for high voltage and capacity. Therefore, accurate and robust modeling of both individual battery cells and their aggregated behavior in battery packs is of crucial importance. This presentation proposes a novel approach to integrate the validated electrochemical-thermal models of the Lithium-ion (Li-ion) cells into battery pack simulations for electric vehicle applications. The approach employs the calibration optimization methodology that utilizes experimental measurements for battery cells and for the battery pack under realistic operating conditions in mining applications. The random variability of battery cells, as well as electrical topology and thermal management of the pack have been considered in the present study to mimic the actual behavior of the battery pack under consideration. The simulations were carried out in GT-AutoLion and the optimizations were performed using GT-SUITE direct optimizer. The experimental data were provided by Northvolt AB, a leading European manufacturer of the next-generation Li-ion battery cells and complete battery systems. The proposed methodology is general and can be applied to other battery chemistries and electric vehicle types to perform multi-objective optimization to predict the performance of large battery packs.
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| 9. |
- Bakchinov, A.A., et al.
(författare)
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Experimental study of the K-regime of breakdown in straight and swept wing boundary layers
- 2000
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Ingår i: Abstracts of 53rd Ann. Meeting of the Div. of Fluid Dyn. APS, Washington, DC.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Experiments on the stability of three-dimensional boundary layers on the straight and swept airfoils have been conducted. Detailed measurements of the streamwise velocity field in (Y, Z) planes, as well as the 3D frequency-wavenumber spectra have revealed linear and non-linear evolutions of the disturbances generated by an external acoustic field in the airfoil boundary layers. The Tollmien-Schlichting waves, excited by the sound, were dominant in both configurations, and the disturbance flow field was found to remain highly deterministic and periodic both in time and space until the latest stages of the transition. To control a spanwise variation of the disturbance flow field roughness elements were placed on the surface and equidistantly aligned along the airfoil leading edge. The K-type transition was identified with the aligned order of so-called Lambda-patterns at non-linear stage of the transition. The experiment was conducted in a closed-circuit wind-tunnel at the department of Thermo and Fluid Dynamics, Calmers. This work was supported by the Royal Swedish Academy of Sciences (KVA).
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