| 1. |
- Arora, Sampann, et al.
(författare)
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A partitioned FSI methodology for analysis of sloshing-induced loads on a fuel tank structure
- 2020
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Ingår i: Proceedings of the 6th European Conference on Computational Mechanics: Solids, Structures and Coupled Problems, ECCM 2018 and 7th European Conference on Computational Fluid Dynamics, ECFD 2018. ; , s. 3037-3048
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Konferensbidrag (refereegranskat)abstract
- Liquid sloshing is a source of major concern in the structural design of containers. In fuel tanks of heavy duty trucks, with capacities of up to 900 litres, this phenomenon is capable of causing fuel to impact the container tank with high forces, and exposing the vulnerable parts of the tank to heavy dynamic loads. This highly non-linear and transient phenomenon is simulated here using the commercial Computational Fluid Dynamics (CFD) code STAR-CCM+. The two phase problem is solved using the VOF interface capturing approach. Owing to the thin walled structures of the fuel tank, it becomes important to account for the effects of Fluid-Structure Interaction (FSI). To this end, a partitioned FSI methodology is employed by coupling the CFD and Finite Element Analysis (FEA) solvers for this multi-physics problem. One-way and two-way coupled FSI methodologies are compared with experimental results. The one-way coupled simulations yield good agreement of wall deformations with the experiments for low filling levels. While the two-way coupled FSI analysis corroborates well with the experiments for all filling levels, its high computational costs render the one-way coupled methodology a promising tool to analyse sloshing for industrial applications. This coupling strategy could inform a fuel tank design suited to prevent structural damage due to sloshing, thus contributing towards its safety and longevity.
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| 2. |
- Etemad, Sassan, et al.
(författare)
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Analysis of developing and fully developed turbulent flow and heat transfer in a square-sectioned U-bend duct
- 2005
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Konferensbidrag (refereegranskat)abstract
- Turbulent flow and thermal field were predicted in a square-sectioned 180° bend at a Reynolds number of 56000. Suga's low-Re cubic k-ε model [5-6] and the RSM [7-8] were used. The results were compared to experimental data [1]. Identical inlet boundary conditions were used in both cases. The inlet length impact on the flow-heat transfer in the bend was investigated. The velocities are higher near the inner wall and lower near the outer wall when a short inlet section is used. As the inlet length increases, the boundary layer grows thicker and the pressure-driven secondary vortex near the side wall becomes stronger. This vortex contributes significantly to the mixing process and heat transfer. It also alters the velocity distribution to a higher velocity near the outer wall and a lower velocity near the inner wall. When using a very long inlet length the vortex grows so strong that it generates a second counter-rotating vortex which isolates the fluid near the inner wall and prevents from further mixing. Consequently the local Nusselt number decreases. Both models reproduced the experimental data fairly well. Suga's model performed better and converged without problems. It is believed that Suga's model would be more suitable for industrial applications.
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| 3. |
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| 4. |
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| 5. |
- Etemad, Sassan
(författare)
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Computational Analysis of Heat Transfer and Fluid Flow with Relevance for IC-Engine Cooling
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Modern IC-engines produce more power per displaced volume and operate at higher combustion pressures and temperatures. In addition, engine structure materials such as aluminium and magnesium alloys, which are more sensitive to thermal loads, are more commonly used. These two parameters might lead to problems such as thermal fatigue, knock, high fuel consumption and emissions, performance loss, bore distortion, oil consumption, noise and vibration. These may, however, be limited by careful design of well-aimed precision engine cooling strategies which provide efficient and sufficient cooling of the extremely hot regions while avoiding over-cooling of the other regions. To enable precision cooling, an accurate and quick prediction tool is needed. CFD has been used during the last decade as a tool for optimization of flow and pressure drop in the IC-engine coolant jackets. There is, however, a need to improve the CFD-methods for more accurate simulations and to extend its benefit to the prediction of the heat transfer. The goal of this work is to contribute to the understanding of the fluid flow and heat transfer mechanisms relevant to IC-engine cooling and to develop CFD methods for realistic predictions of the heat transfer coefficient for this kind of application. In this work the flow and heat transfer processes have been investigated for well known generic cases relevant to the engine cooling applications. These cases consist of confined flow in curved ducts with various cross section shapes. The performance of several turbulence models including different versions of high- and low-Reynolds number two-equation models, mostly k-epsilon models, with linear and non-linear Reynolds stress formulations and also V2F and RSM have been investigated. Wall functions, damping functions and a two-layer technique were used for wall treatment. Available experimental data in the literature have been used for validation of these studies. The strengths and weaknesses of these models are discussed in the thesis. The focus has been on forced convection heat transfer. The impact of parameters such as inlet boundary conditions and duct cross-section shape on the flow and heat transfer has also been studied. It was found that these parameters, especially the upstream boundary conditions have significant influence on the pressure-driven secondary flow and, thereby, the heat transfer mechanism in curved ducts. The convergence problem of V2F and the RSM and the physical shortcomings of linear eddy viscosity models as well as the robustness of models like Suga's cubic low-Re k-epsilon model and Chen's k-epsilon model have been discussed. Finally full scale IC-engine cooling analyses utilizing some of the gained experiences from the more fundamental work have been presented.
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| 6. |
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| 7. |
- Etemad, Sassan, et al.
(författare)
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Hydraulic and Thermal Simulations of a Cross-Corrugated Plate Heat Exchanger Unitary Cell
- 2016
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Ingår i: Heat Transfer Engineering. - : Informa UK Limited. - 1521-0537 .- 0145-7632. ; 37:5, s. 475-486
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Tidskriftsartikel (refereegranskat)abstract
- Simulations have been carried out by means of computational fluid dynamics for turbulent convective heat transfer in a cross-corrugated plate pattern heat exchanger unitary cell at a Reynolds number of 4930. Chen's high-Reynolds-number k-E model, the Reynolds stress model (RSM), Suga's low-Reynolds-number k-E model, and the V2F model were used. The predicted hydraulic and thermal behaviors using these models have been compared and explained. The simulations showed that the interaction between the upper flow and lower flow in the cell creates a shear zone at their interface with a rotating motion and as a consequence the heat transfer is enhanced. This phenomenon was captured best by the V2F model, which predicted the highest Nusselt number and friction factor. Chen's k-E model provided results similar to the RSM. The fact that the RSM was instable and required more computational power makes it less interesting for further use in similar studies. It was also found rewarding to generate multiblock all-hexahedral grids to resolve the existing thermal and hydraulic phenomena in the domain.
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| 8. |
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| 9. |
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| 10. |
- Etemad, Sassan, et al.
(författare)
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Numerical investigation of turbulent heat transfer in a rectangular-sectioned 90 degrees bend
- 2006
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Ingår i: Numerical Heat Transfer Part A: Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 49:4, s. 323-343
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Tidskriftsartikel (refereegranskat)abstract
- The flow and thermal fields in a rectangular-sectioned 90 degrees bend with a cross-section aspect ratio of 6 were investigated using four turbulence models. All models managed to reproduce the general flow and thermal patterns. Chen's high-Re k-epsilon model and Suga's cubic low-Re k-epsilon model performed well. The V2F k-epsilon model was found to be the least diffusive model and delivered good results. The RSM-GGDH model showed convergence difficulties and gave poor results. It was found that the boundary-layer thickness and the flow upstream of the bend are crucial for the character of the secondary flow, velocity profile, turbulence level, and heat transfer in the bend.
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| 11. |
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| 12. |
- Etemad, Sassan, et al.
(författare)
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Turbulent flow and heat transfer in a square-sectioned U-bend
- 2006
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Ingår i: Progress in Computational Fluid Dynamics, An International Journal. - 1741-5233. ; 6:1-3, s. 89-100
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Tidskriftsartikel (refereegranskat)abstract
- Turbulent flow and heat transfer in a square-sectioned U-bend are investigated. Turbulence models with linear and non-linear expressions for the Reynolds stresses are used. The near wall turbulence is treated by the damping functions approach and a two-layer model with Wolfshtein's sub-layer treatment. The inlet conditions have a significant effect on the predictions. The results from the non-linear low-Reynolds number k-epsilon models including Suga's cubic low-Re model were closest to experimental data. These models predicted the stress-induced secondary motion in the straight inlet duct well. This secondary motion had a small impact on the flow in the bend.
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| 13. |
- Ghosh, Debarshee, 1995, et al.
(författare)
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Aerodynamic Analysis of Low-Pressure Axial Fans Installed in Parallel
- 2024
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Ingår i: Journal of Fluids Engineering, Transactions of the ASME. - 1528-901X .- 0098-2202. ; 146:5
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Tidskriftsartikel (refereegranskat)abstract
- Ducted rotor-only low-pressure axial fans play an integral role in automotive thermal management. The tightly packed under-hood region and down-stream heat-exchanger shape limit the fan diameter. In order to circumvent this limitation, multiple cooling fans of small diameters are tightly packaged and placed in parallel. Currently, there is limited scientific work, that study the aerodynamics of low-pressure axial fans when installed in parallel. This work aims to quantify the aerodynamic performance and the flow-field as a result of installing low-pressure axial fans in parallel through computational fluid dynamics (CFD). Publicly available experimental data from Friedrich-Alexander University is used for the validation of the numerical setup. Three-dimensional, full-annulus, unsteady Reynolds-averaged Navier‐Stokes (URANS) analysis has been performed for both a single-fan and two-fans installed in parallel and their respective aerodynamic performance has been compared for the operation condition identified as the best efficiency point in experiments. Only small differences are observed in the overall aerodynamic performance of the two-fans in parallel compared to a single-fan. A circumferential nonuniformity in the form of a local high-pressure zone at the inlet of the fan is observed when the two-fans are placed in parallel. The resulting circumferential nonuniformity is quantified, both in space and time. A strong correlation is found between the pressure fields of the two-fans installed in parallel.
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| 14. |
- Ghosh, Debarshee, 1995, et al.
(författare)
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Computational Fluid Dynamics Simulations of Aerodynamic Performance of Low-Pressure Axial Fans with Upstream Blockage
- 2024
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Ingår i: SAE Technical Papers. - 0148-7191 .- 2688-3627.
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Konferensbidrag (refereegranskat)abstract
- Rotor-only ducted low-pressure axial fans play a crucial role in automotive thermal management of the tightly packed under-hood region. Most current scientific work concerning low-pressure axial fans investigate the aerodynamic performance of these fans while operating with uniform inlet flow conditions. This is rarely the case in real-world applications. This work aims to investigate the aerodynamic performance of low-pressure axial fans operating with upstream blockages. First, a validation study is performed in the absence of any upstream blockage. Numerical results are compared against publicly available experimental data. Steady-state, Reynolds-Averaged Navier Stokes (RANS) analysis is performed on a single-blade passage. The validation study also evaluates the choice of turbulence model and suggests the use of the k- ε turbulence model with wall functions for the best comparison against experimental data. To study the effect of upstream blockage, a generic blockage disc is positioned upstream of the fan inlet. Three different radial extents of the blockage disc is evaluated, such that different radial extents of the blade span is blocked. A strong influence of the upstream blockage is observed on the fan performance and flow distribution along the blade span. The total-to-static pressure coefficient and the total-to-static efficiency decrease proportionately to the extent of blockage in the radial direction. The peak total-to-static efficiency moves to a lower flow coefficient with increase in upstream flow blockage. This is deemed undesirable for automotive applications where it is desirable to have maximum aerodynamic efficiency at the highest possible flow coefficient.
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| 15. |
- Karlsson, Mikael, et al.
(författare)
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Installation Effects on the Flow Generated Noise from Automotive Electrical Cooling Fans
- 2020
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Ingår i: SAE technical paper series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191. ; :2020
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Tidskriftsartikel (refereegranskat)abstract
- With the electrification of road vehicles comes new demands on the cooling system. Not the least when it comes to noise. Less masking from the driveline and new features, as for example, cooling when charging the batteries drives the need for silent cooling fans. In this work a cluster installation of electrical fans is studied in different generalized installations and operating conditions. The fans are installed in a test rig where the operation could be controlled varying the speed, flow rate and pressure rise over the fan. On the vehicle side of the fan a generalized packaging space (similar to an engine bay for conventional vehicles) is placed. In this packaging space different obstruction can be placed to simulate the components and radiators used in the vehicle. Here generalized simple blocks in different configuration are used to provide well defined and distinct test cases. Of special interest are cases with poor inlet flow profile and the influence of this on the sound generation. Noise results are compared to scaling laws for the influence of fan speed, efficiency and clustering. It is shown that the fans are not so sensitive to the downstream installation as long as they are not run in an extreme end of the efficiency curve. For engineering use a scaling law with relative fan speed is sufficient. More unexpected results are seen when clustering the fans. The cluster makes more noise than the individual fans suggest. It was also found that deactivating two of the four fans actually increases the noise in the tested installation. These clustering effects are believed to be due to non-uniform inlet flow with increased turbulence levels.
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| 16. |
- Ramesh Babu, Anandh, 1996, et al.
(författare)
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An adaptive cabin air recirculation strategy for an electric truck using a coupled CFD-thermoregulation approach
- 2024
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Ingår i: International Journal of Heat and Mass Transfer. - 0017-9310. ; 221
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Tidskriftsartikel (refereegranskat)abstract
- Cabin climatization is one of the largest auxiliary loads in an electric vehicle, and its performance significantly affects the driving range. Recirculating climatized air from the cabin has been shown to reduce energy consumption, but at the risk of fogging the windows and deteriorating the air quality. Therefore, many automobile manufacturers refrain from adopting it at low ambient temperatures. In this paper, an adaptive recirculation strategy that takes these issues into account is proposed and studied on an electric truck cabin while heating. Numerical simulations were performed using a coupled CFD-thermoregulation model, with the consideration of humidity and CO2. The JOS-3 thermoregulation model was employed for estimations of skin temperatures and evaporation of vapor from the skin, and the Berkeley comfort model was used to evaluate the comfort metrics. Ten scenarios were considered at various vehicle speeds, temperatures, and relative humidity levels while evaluating them with and without the proposed return-air strategy. The controller adapted between humidity and CO2-critical conditions during run-time. The fresh-air mass flow requirements reduced with increasing difference between the setpoint and ambient vapor mass fractions under humidity critical conditions, and plateaued at 10 g/s where CO2 was more critical. The proposed strategy provided energy savings ranging from 9% to 34% depending on the operating condition.
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| 17. |
- Vasudevan, Sudharsan, 1991, et al.
(författare)
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Comparative analysis of single and multiphase numerical frameworks for subcooled boiling flow in an internal combustion engine coolant jacket
- 2023
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311. ; 219
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Tidskriftsartikel (refereegranskat)abstract
- Computational analysis of nucleate boiling occurring in liquid cooled applications, such as internal combustion engines is often implemented within a single phase Computational Fluid Dynamics (CFD) framework, owing to low vapor fractions involved. With increase in specific power and the resulting higher thermal loads, accounting for the presence of the vapor phase using a multiphase framework is required in certain conditions, despite the higher computational costs. While detailed resolution of the liquid and vapor phases in nucleate boiling using a two fluid model is excessively computationally expensive, the homogeneous mixture multiphase framework is a good compromise between resolution and computational cost. In this article a numerical wall boiling model is implemented within both, a single phase and the mixture multiphase frameworks. Results from the two approaches are compared with measurements in a channel flow. The results from both approaches are in good agreement with experiments. The single phase approximation is valid when the vapor generation is low. The sensitivity of the results to the computational grid is also discussed in detail. Further, the two frameworks are used to simulate the heat transfer in the coolant jacket of a four-cylinder petrol engine. The results from the numerical simulations are compared with measurements. Both computational frameworks compare reasonably well with the measurements in terms of local metal temperature. However, the advantage of accounting for the vapor phase using the mixture multiphase framework is evident when the parameter related to vapor bubble interactions is analyzed in detail.
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| 18. |
- Vasudevan, Sudharsan, 1991, et al.
(författare)
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Improved estimation of subcooled flow boiling heat flux for automotive engine cooling applications
- 2019
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Ingår i: ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference, AJKFluids 2019. ; 3A-2019
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Konferensbidrag (refereegranskat)abstract
- Tapping the potential of subcooled flow boiling can be the key strategy for enhanced cooling of modern day internal combustion engines with high specific power. Accurate prediction of the boiling heat flux is a prerequisite for employing such strategy and to avoid stepping into the dangerous film boiling regime. The complexity involved in the boiling phenomena makes it difficult to develop a model that accounts for all the dominant mechanisms. However, boiling models available in literature provide a good estimate of the heat flux within their range of applicability. This work attempts to introduce a blending based on probability of bubble nucleation to blend two different models developed for different boiling regimes. Corroboration of results with experiments show improved estimation of boiling heat flux.
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| 19. |
- Vasudevan, Sudharsan, 1991, et al.
(författare)
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Numerical model to estimate subcooled flow boiling heat flux and to indicate vapor bubble interaction
- 2021
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Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 170
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Tidskriftsartikel (refereegranskat)abstract
- There are numerous technical applications where hot components, with uneven temperature distribution, require cooling. In such applications, it is desired to provide efficient local cooling of the hot spots, while avoiding unnecessary over-cooling of the other regions. Such an approach, known as precision cooling, has several advantages. In addition to the fact that it reduces the effort for cooling, it limits the unintended heat lost to the cooling medium. In liquid cooled systems, such as Internal Combustion Engines (ICE), subcooled flow boiling offers immense potential for precision cooling. The primary challenges in extracting this potential are understanding the complexities in the subcooled flow boiling phenomenon and estimating the risk of encountering film boiling. The present study introduces a numerical model to estimate the wall heat flux in subcooled flow boiling and the model includes a mechanistic formulation to account for vapor bubble interaction. The formulation for vapor bubble interaction serves two purposes: (a) blends two well-established models in the literature, one in the isolated bubbles regime and other in the fully developed boiling regime, to estimate the wall heat flux; and (b) provides information to limit boiling in order to not encounter film boiling. The results from the new model are validated with two different experiments in the literature and the wall heat flux estimated by the model is in agreement with experimental results and responsive to different input parameters, such as bulk velocity, operating pressure and inlet subcooling. The new model requires only input of local flow quantities and hence implementation in Computational Fluid Dynamics (CFD) is straightforward.
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