| 1. |
- Bovo, Mirko, 1979, et al.
(författare)
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Direct comparison of les and experiment of a single-pulse impinging jet
- 2015
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Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 88, s. 102-110
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Tidskriftsartikel (refereegranskat)abstract
- Experimental results are commonly used to validate numerical simulations. Often, it is challenging to accurately reproduce the experimental setups in the numerical environment, thereby leaving uncertainty in the validation process. An experiment on impinging jets was designed with boundary conditions well suited for implementation in the numerical environment. In this work, LES was implemented to specifically match the experiment of a single-pulse jet impinging on a surface oriented normally to the jet axis. The experiment was designed primarily to study the thermal effects on the impingement zone with high space-time resolution. The temperature evolution of the impingement target was measured via IR camera. The space-time resolved jet velocity-field was measured with PIV and was used as boundary condition for the simulation. The focus of the LES was to replicate the experiment as faithfully as possible in the virtual environment. LES was run multiple times to allow statistical evaluation of the results, as done in the experimental procedure. High levels of agreement were found between the LES and the experimental results, both from a qualitative and a quantitative point of view. This work could therefore be considered as a successful validation of the LES in the study of this type of flows.
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| 2. |
- Bovo, Mirko, 1979, et al.
(författare)
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Measurements of a single pulse impinging jet. A CFD reference
- 2014
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. - 9788026053750 ; 67
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Konferensbidrag (refereegranskat)abstract
- This paper reports three sets of measurements of a single pulse impinging jet. The purpose is to serve as a reference for CFD validation. A gas injector generates a single pulse jet at Re ~90000. The jet impinges on a temperature controlled flat target at different angles (0̈, 30̈, 45̈ and 60̈). The jet velocity field is measured with PIV. The evolution of the jet velocity profile in time is reported at two different locations (suitable as CFD inlet conditions). At the same locations also turbulence quantities are reported. The impingement wall temperature is measured with fast responding thermocouples and infrared camera. These give high time and space resolution respectively. Results are reported in a format suitable for comparison with CFD simulations. The results show that the heat transfer effects are highest for the jet impinging normally on the target. Target inclination has remarkable effects on the jet penetration rate and repeatability. Even small target inclinations result creates a preferential direction for the jet flow and cause a shift in the position of the stagnation region.
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| 3. |
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| 4. |
- Bovo, Mirko, 1979, et al.
(författare)
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On the Numerical Modeling of Impinging Jets Heat Transfer - A Practical Approach
- 2013
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Ingår i: Numerical Heat Transfer Part A: Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 64:4, s. 290-316
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Tidskriftsartikel (refereegranskat)abstract
- This article compares steady-state and transient simulations in predicting impinging jet heat transfer. The configurations tested are H/D=2 and 6, Re=10,000, 20,000, 23,000, and 30,000. The variables considered are: turbulence model (LES, k-E, k-, V2F), discretization schemes, mesh density and topology, inlet velocity profile, and turbulence. The V2F model performs best for the steady state simulations. The inlet velocity profile plays an important role. Mesh topology and distribution is also important. The turbulence created in the shear layer plays a stronger role than the inlet turbulence. The LES model reproduces the turbulent structures with a useful degree of accuracy.
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| 5. |
- Bovo, Mirko, 1979
(författare)
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On the numerical modelling of impinging jets heat transfer
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis collects two studies on heat transfer in impinging jets and on methods for modeling flows of this kind using CFD. Stationary impinging jets with different nozzle to wall distances (z/D = 2 and 6) and Re (10000, 20000, 23000, 30000) are modeled. Steady-state models capture the important features of heat transfer in these jets. The inlet velocity profile plays an important role on the results. The k-ε and k-ω turbulence models do not offer adequate performance. However, the V2F model generates useful results even with low order discretization schemes. The effects of varying the mesh density and topology also studied, and the computational cost of different model set-ups is compared. Transient simulations were shown to be useful for studying the dynamics of turbulent flow in the impinging jet shear layer. Simulations are performed using the LES model, which resolves the turbulent fluctuations, and with the DES, V2F, and k-ε turbulence models, which do not; a number of parameters are varied during the testing of the LES model. The effects of inlet turbulence were studied by superimposing synthetic turbulent fluctuations at the inlet. The LES, DES and V2F models are shown to capture the time-average heat transfer coefficient in a fashion that agreed well with the available experimental data.
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| 6. |
- Bovo, Mirko, 1979, et al.
(författare)
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On the transient modelling of impinging jets heat transfer. A practical approach
- 2012
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Ingår i: Proceedings of the International Symposium on Turbulence, Heat and Mass Transfer. - 2377-2816. ; 2012-September, s. 397-408
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Konferensbidrag (refereegranskat)abstract
- This work compares a number of CFD transient models of an impinging jet with both LES and URANS models. The specific case considered is that of an impinging jet with H/D = 6 and Re 23000. The study spans over a wide number of variables for the purpose to access and directly compare different approaches. The variables tested are: turbulence model (LES Smagorinsky, standard low Reynolds k-ε and V2F), numerical discretization schemes, mesh density (total cell number and local cell distribution), synthetic turbulence inlet fluctuations. The model assessment is based on the comparison with available experiments for wall heat transfer and flow turbulent quantities. The computational cost is also considered for completeness.
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| 7. |
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| 8. |
- Bovo, Mirko, 1979, et al.
(författare)
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Single pulse jet impingement on inclined surface, heat transfer and flow field
- 2013
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- This paper focuses on the heat transfer and flow field resulting from a single pulse impinging jet. The size, time scale and jet characteristics are relevant to automotive diesel injection process. The purpose is to study jet impingement by correlating and cross comparing different measurements and simulations of the same event. The pulse jet impinges on a flat surface at different angles (0°, 30°, 45°, 60°) and a 90° rounded edge. Experiments are performed deploying various techniques to record the event; PIV for the flow field, high acquisition rate thermocouples and infrared camera for surface temperature. The cases are reproduced with CFD simulations including conjugated heat transfer. The flow is simulated using LES. The results highlight that the jet penetration rate is a function of the target angle. Also, the heat transfer magnitude and space distribution depends on the surface inclination. Alongside, the consistency of the results validates CFD as a powerful tool to study this type of flow.
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| 9. |
- Båstedt, Peter, et al.
(författare)
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Subcooled Flow Boiling in High Power Density Internal Combustion Engines I: Thermal Survey Measurement Campaign
- 2022
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Ingår i: SAE International Journal of Engines. - : SAE International. - 1946-3944 .- 1946-3936. ; 16:1
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Tidskriftsartikel (refereegranskat)abstract
- Nucleate boiling occurs inadvertently in the coolant jacket of high power density internal combustion engines, especially in vicinity of regions experiencing high thermal loads. Occurrence of boiling can be beneficial and be an efficient way to improve heat transfer locally near hot spots, but excessive boiling can be detrimental to structural integrity of the engine. While most of the efforts to understand boiling have been focused on experiments in simplified geometries, this article presents results from thermal survey measurement on a production engine. The purpose of the measurement campaign is to understand the intensity and extent of nucleate boiling occurring in different parts of the engine coolant jacket. This is achieved by sweeping across different input parameters, such as engine operating load point, cooling system operating pressure, coolant flow rate, and coolant inlet temperature. Different boiling regimes are encountered in different parts of the coolant jacket. A wide database of local solid temperatures measured at several critical locations is obtained and these results are interpreted in line with the underlying physics of subcooled flow boiling. The database not only helps to understand the boiling phenomenon occurring in engine coolant jacket, but is also used to calibrate a numerical boiling model.
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| 10. |
- Somhorst, Joop, et al.
(författare)
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A Method to Evaluate the Compression Ratio in IC Engines with Porous Thermal Barrier Coatings
- 2018
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 2018-September
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Tidskriftsartikel (refereegranskat)abstract
- The compression ratio is an important engine design parameter. It determines to a large extend engine properties like the achievable efficiency, the heat losses from the combustion chamber and the exhaust losses. The same properties are affected by insulation of the combustion chamber. It is therefore especially important to know the compression ratio when doing experiments with thermal barrier coatings (TBC). In case of porous TBCs, the standard methods to measure the compression ratio can give wrong results. When measuring the compression ratio by volume, using a liquid, it is uncertain if the liquid fills the total porous volume of the coating. And for a thermodynamic compression ratio estimation, a model for the heat losses is needed, which is not available when doing experiments with insulation. The subject of this paper is the evaluation of an alternative method to assess the compression ratio. It is based on motored cylinder pressure data like other thermodynamic methods but does not need a model for the heat losses. The validation and application of the method is done with data from experiments involving two types of porous TBCs, performed on a light duty single cylinder diesel engine. The results indicate that the proposed method accurately predicts the compression ratio for porous thermal barrier coatings.
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| 11. |
- Somhorst, Joop, et al.
(författare)
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Experimental Evaluation of Novel Thermal Barrier Coatings in a Single Cylinder Light Duty Diesel Engine
- 2019
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Ingår i: SAE technical paper series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627.
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this investigation was to improve the thermal properties of plasma sprayed thermal barrier coatings (TBC) for internal combustion engines. There is a need for further reduction of thermal conductivity and volumetric heat capacity and the negative effects on heat loss and combustion phasing of surface roughness and permeable porosity, typical for plasma sprayed coatings, should be minimized. Four measures for improvement of TBC properties were evaluated: I) modification of the coating’s microstructure by using a novel suspension plasma spraying method, ii) application of gadolinium-zirconate, a novel ceramic material with low thermal conductivity, iii) polishing of the coating to achieve low surface roughness, and iv) sealing of the porous coating surface with a polysilazane. Six coating variants with different combinations of the selected measures were applied on the piston crown and evaluated in a single cylinder light duty diesel engine. The experimental data was modeled with multiple linear regression to obtain confidence intervals for the measurement results and to correct the data for variations of surface roughness, combustion phasing and compression ratio for the different pistons. The main tool for evaluation of the coating properties was cylinder pressure analysis, providing the apparent rate of heat release, indicated efficiency, wall heat loss, and exhaust loss. The new TBC microstructure from suspension plasma spraying in combination with the use of gadolinium-zirconate showed promising results with respect to indicated efficiency and heat loss reduction. © 2019 SAE International and © 2019 SAE Naples Section. All rights reserved.
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| 12. |
- 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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| 13. |
- Vasudevan, Sudharsan, 1991, et al.
(författare)
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Subcooled Flow Boiling in High Power Density Internal Combustion Engines II: Numerical Modeling
- 2022
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Ingår i: SAE International Journal of Engines. - : SAE International. - 1946-3944 .- 1946-3936. ; 16:1
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Tidskriftsartikel (refereegranskat)abstract
- Results from a thermal survey measurement campaign on a four-cylinder Volvo engine was presented in Part I of this article. The focus was predominantly on heat transfer in the engine coolant jacket. This part presents numerical modeling focused specifically on the coolant flow and associated heat transfer in the coolant jacket using computational fluid dynamics (CFD), as a part of a high-resolution complete engine 3D conjugate heat transfer (CHT) model. With local nucleate boiling being an indispensable phenomenon in high power density engines, a dedicated boiling model is essential and is to be used in conjunction with CFD while analyzing heat transfer in the coolant jacket. This article validates a new boiling model with data obtained from the extensive thermal survey measurements, presented in Part I. The new model includes a parameter, based on vapor bubble interactions, that serves as an indication of the transition from beneficial nucleate boiling to high-risk transition and film boiling regimes. This parameter might be used to assess the robustness of new engine designs. The advantages and limitations of the new boiling model are presented and are discussed in detail.
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