| 1. |
- Liu, Yan, et al.
(författare)
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3D CFD Modelling of Sintering of Metal Binder Jetting Products
- 2022
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Ingår i: World PM 2022 Congress Proceedings.
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Konferensbidrag (refereegranskat)abstract
- Binder jetting process is a prominent 3D printing technology due to its cost-effectiveness and capability to scale up the production in terms of batch sizes. However, the green parts need several post-processes including curing, debinding and sintering to improve the parts' density and mechanical strength. These post-processes bring many challenges affecting the final part size and dimensional accuracy. To get the best result and desired material properties, precise temperature and atmosphere control are vital during each individual post-process. This work shows 3D computational fluid dynamics (CFD) as a powerful tool to achieve such an objective. A full-scale 3D CFD simulation method of a sintering furnace in operation will be presented. This method allows 3D calculation of all the important processes including gas flow, thermal radiation, convection and conjugate heat transfer in solids and fluids so that sintering processes of metal binder jetting products can be well simulated.
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| 2. |
- Liu, Yan, et al.
(författare)
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Simulation and Additive Manufacturing of Complexly Designed Aircraft Component
- 2023
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Ingår i: Euro PM2023 Proceedings. - : European Powder Metallurgy Association (EPMA).
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Konferensbidrag (refereegranskat)abstract
- An innovative component used for the cargo handling systems of Boeing 737 aircraft is developed to improve loaders’ working conditions and protect cargo spaces, passenger luggage, and goods from damage. Since the design of the component makes it difficult to manufacture using conventional techniques, metal Binder Jetting, an Additive Manufacturing technique both faster and more cost-effective compared to the conventional laser/electron beam techniques, is used. However, there is a risk of thermally induced distortion in connection with the post-processing, specifically the sintering step. To address this, a 3D computational fluid dynamics simulation model is developed and simulations are made to identify where and when unwanted distortions may occur during the sintering process. In the simulation, the sintering process follows about 15 hours full sintering cycle with all the heating, holding and cooling stages. The simulations are compared with experiments to validate the numerical results.
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| 3. |
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| 4. |
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| 5. |
- Holmstedt, Göran, et al.
(författare)
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Determination of uncertainty of different CFD codes by means of comparison with experimental fire scenarios
- 2009
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Ingår i: Conference Proceedings - Fire and Materials 2009, 11th International Conference and Exhibition.
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Konferensbidrag (refereegranskat)abstract
- This article will summarise the evaluation of four CFD software codes (CFX, FDS4, SMAFS and SOFIE). Evaluation was performed by means of comparing the simulation data with experimental scenarios. The scenarios were chosen to represent scenarios frequently assessed using fire safety design based on performance. The greatest difficulty during validation of CFD-codes is to find well documented relevant experiments. It is true that many large scale experiments including smoke spread have been published but many of them are not described sufficiently and are therefore impossible to use for validation. It is very unusual that data on reproducibility and repeatability is available. After an extensive discussion between the participants in the project five scenarios were chosen. Scenarios 1A (large room with vents), and scenarios 1B1 and 1B2 (corridor with vents) were well documented experiments (repeatability) with ceiling vents and ceiling jets performed earlier at SP in Boras. Scenario 2 is a tunnel fire taken from an experimental study in Boston, US. Scenario 3 is an atrium fire taken from an experimental study in Japan. Lack of well documented fires in retail premises lead us to perform a series of tests in 1/2 scale, 4.1 and 4.2 at SP in Boras. Scenario 5 is an experimental study from Australia including smoke spread from a fire room to an adjacent corridor and a room. The conditions for the simulations included information about the scenarios given above. No information about experimental results was available until the results from the simulations had been sent in to the project manager. The intention was to imitate the working conditions for a consultant as far as possible when using a CFD-simulation to estimate fire safety. In this manner the simulations are dependent on many factors such as the CFD-code used, judgement of input data of the scenarios done by the operator, operator skill etc. The results from the evaluation of the CFD codes showed that the simulation results generally were a good description of the experimental fires studied, but that limitations and specific properties of the different codes, together with the operator factor, can strongly influence the results. The detailed results of all comparisons are given in the final report of the project. It was not possible to include these detailed evaluations in this conference paper but these results are available in the main report as well as in future scientific articles.
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| 6. |
- Li, Songyang, et al.
(författare)
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Theoretical and experimental analysis of ceiling-jet flow in corridor fires
- 2011
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Ingår i: Tunnelling and Underground Space Technology. - : Elsevier BV. - 1878-4364 .- 0886-7798. ; 26:6, s. 651-658
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Tidskriftsartikel (refereegranskat)abstract
- In tunnels or long corridors, the combustion products of the fire are confined to spread in one or two directions, forming a ceiling-jet flow. For safety assessment and emergency treatment, it is important to investigate and understand the behavior of the ceiling-jet flow. In this paper, a simple model has been presented, in terms of Richardson number and non-dimensional ceiling-jet thickness, to predict the temperature and the velocity of fire-induced ceiling-jet in a rectangular corridor. Besides, the location of hydraulic jump, occurring in ceiling-jet flow, has been estimated theoretically. In order to validate the theoretical predictions, a series of reduced-scale fire experiments were conducted in a 5 m long corridor. The predicted results, concerning non-dimensional excess temperature, agree favorably with experimental data in different fuels and heat release rates of the fire tests. Finally, the scaling issue has also been discussed and validated. (C) 2011 Elsevier Ltd. All rights reserved.
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| 7. |
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| 8. |
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| 9. |
- Yan, Zhenghua
(författare)
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A fast spectral approximation of narrow-band model for thermal radiation calculation
- 2004
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Ingår i: Numerical Heat Transfer Part B: Fundamentals. - : Informa UK Limited. - 1040-7790 .- 1521-0626. ; 46:2, s. 165-178
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Tidskriftsartikel (refereegranskat)abstract
- A fast spectral approximation of a narrow-band computer model is proposed for prediction of thermal radiation in a generally nonisothermal and nonhomogeneous combustion environment. The approximation is made by assuming each discretized spatial element along a line of sight to be locally "gray" within each small narrow-band spectrum interval. For each spatial element, the local equivalent spectral absorption coefficient of the combustion products, including carbon dioxide, water vapor, and soot, is calculated based on formulas from the narrow-band model. Compared with the previously developed fast narrow-band model, FASTNB, which is an order of magnitude faster and gives almost exactly the same result as Grosshandler's original narrow-band model RADCAL, this approximation method provides calculation result with small deviation at substantially faster speed. Furthermore, the speed-up ratio increases linearly with the number of discretized spatial elements along a line of sight. This makes this approximation method particularly useful in computational combustion, where the grid number used in computation is steadily becoming larger and larger as the computation goes toward large eddy simulation (LES) and direct numerical simulation (DNS).
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| 10. |
- Yan, Zhenghua
(författare)
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A numerical study of effect of initial condition on large eddy simulation of thermal plume
- 2003
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Ingår i: Numerical Heat Transfer Part B: Fundamentals. - : Informa UK Limited. - 1040-7790 .- 1521-0626. ; 43:2, s. 167-178
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Tidskriftsartikel (refereegranskat)abstract
- Large eddy simulations of thermal plume in two different scenarios have been carried out using a self-developed parallel computational fluid dynamics (CFD) code, SMAFS (Smoke Movement And Flame Spread), with subgrid-scale turbulence modeled using the Smagorinsky model. Two different initial conditions were used in the simulations, and the results were compared to show that the initial condition has a significant effect on the prediction of the plume's evolution behavior. The filtered governing equations were discretized using the finite-volume method, with the variables at the cell faces in the finite-volume discrete equations approximated by a second-order bounded QUICK scheme and the diffusion term computed based on the central difference scheme. All the computations were explicitly time-marched, with the momentum equations solved based on a second-order fractional-step Adams-Bashford scheme and the enthalpy computed using a second-order Runge-Kutta method. The Poisson equation for pressure from the continuity equation was solved using a multigrid solver.
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| 11. |
- Yan, Zhenghua, et al.
(författare)
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A two-equation turbulence model and its application to a buoyant diffusion flame
- 1999
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Ingår i: International Journal of Heat and Mass Transfer. - 0017-9310. ; 42:7, s. 1305-1315
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Tidskriftsartikel (refereegranskat)abstract
- A modified k–ε two-equation turbulence model was developed to improve the consideration of the important buoyancy effect on turbulence and turbulent transport, which is a serious deficiency of the standard buoyancy-modified k–ε model. The present model was tested against both plane and axisymmetric thermal plumes and a buoyant diffusion flame. The model was found to be stable, computationally economic, promising and applicable to complex situations. The predicted plume spreading rates and velocity and temperature profiles agreed well with experimental measurements. When compared with the standard buoyancy-modified k–ε turbulence model, this model gives significantly improved numerical results.
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| 12. |
- Yan, Zhenghua, et al.
(författare)
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Analysis of Flame Radiative Heat Transfer Using Large Eddy Simulation
- 2009
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Ingår i: HT2009: PROCEEDINGS OF THE ASME SUMMER HEAT TRANSFER CONFERENCE 2009, VOL 1. - 9780791843567 ; , s. 177-186
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Konferensbidrag (refereegranskat)abstract
- Abstract in UndeterminedA series of comprehensive large eddy simulations of non-premixed turbulent hydrocarbon flames of different sizes in a typical fire scenario have been carried out to compute the flame radiative heat transfer. In the simulation, considerations include the modelling of sub-grid turbulence, turbulent combustion, soot formation, thermal radiation and interactive heat transfer inside solid walls, etc. The instantaneous thermal radiation was calculated using the discrete transfer method with the radiation property evaluated by both an approximated fast narrow band model and an integral model. Simulation was validated against experimental data. Flame radiation heat transfer was compared for flames of different sizes. The effect of thermal radiation property evaluation model on calculation of radiation and the role of thermal radiation in total heat transfer are analyzed.
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| 13. |
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| 14. |
- Yan, Zhenghua, et al.
(författare)
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CFD and experimental studies of room fire growth on wall lining materials
- 1996
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Ingår i: Fire Safety Journal. - 0379-7112. ; 27:3, s. 201-238
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Tidskriftsartikel (refereegranskat)abstract
- CFD simulation and experimental tests have been carried out to study the room corner fire growth on combustible wall-lining materials. In the CFD simulation, the turbulent mass and heat transfer, and combustion were considered. The discrete transfer (DT) method was employed to calculate the radiation with an absorptivity and emissivity model employed to predict the radiation property of combustion products including soot, CO2 and H2O, which are usually the primary radiating species in the combustion of hydrocarbon fuels. The temperature of the solid boundary was determined by numerical solution of the heat conduction equation. A simple and practical pyrolysis model was developed to describe the response of the solid fuel. This pyrolysis model was first tested against the Cone Calorimeter data for both charring and non-charring materials under different irradiance levels and then coupled to CFD calculations. Both full and one-third scale room corner fire growths on particle board were modelled with CFD. The calculation was tested with various numbers of rays and grid sizes, showing that the present choice gives practically grid- and ray number-independent predictions. The heat release rate, wall surface temperature, char depth, gas temperature and radiation flux are compared with experimental measurements. The results are reasonable and the comparison between prediction and experiment is fairly good and promising.
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| 15. |
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| 16. |
- Yan, Zhenghua
(författare)
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Comprehensive CFD Simulation of Fire in a Retail Premise with Analysis of Leakage Effect
- 2009
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Ingår i: Numerical Heat Transfer. - : Informa UK Limited. ; 55:1, s. 1-17
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Comprehensive simulations of fire in a retail premise from a blind validation study are presented. The simulations were made using a self-developed parallel CFD program SMAFS [1], with the turbulent flow, turbulent combustion, thermal radiation, soot formation, and the interactive heat transfer inside solid boundary all computed. The results are extensively compared with experimental measurement showing good agreement. Detailed result analysis shows the important effect of flow leakage in such a fire scenario. It is found that the leakage can alter the ventilation condition and has important influence on the gas temperature profile at low height and the flow profile at the ventilation opening. This indicates that care should be taken with the consideration of leakage in a proper CFD simulation of fire in relevant scenarios.
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| 17. |
- Yan, Zhenghua, et al.
(författare)
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Fast, narrow-band computer model for radiation calculations
- 1997
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Ingår i: Numerical Heat Transfer Part B: Fundamentals. - : Informa UK Limited. - 1040-7790 .- 1521-0626. ; 31:1, s. 61-71
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Tidskriftsartikel (refereegranskat)abstract
- A fast, narrow-band computer model, FASTNB, which predicts the radiation intensity in a general nonisothermal and nonhomogeneous combustion environment, has been developed. The spectral absorption coefficients of the combustion products, including carbon dioxide, water vapor, and soot, are calculated based on the narrow-band model. FASTNB provides an accurate calculation at reasonably high speed. Compared with Grosshandler's narrowband model, RADCAL, which has been verified quite extensively against experimental measurements, FASTNB is more than 20 times faster and gives almost exactly the same results.
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| 18. |
- Yan, Zhenghua, et al.
(författare)
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Large eddy simulation of natural convection along a vertical isothermal surface
- 2005
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Ingår i: Heat and Mass Transfer. - : Springer Science and Business Media LLC. - 1432-1181 .- 0947-7411. ; 41:11, s. 1004-1013
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Tidskriftsartikel (refereegranskat)abstract
- Large eddy simulations of natural convection along a vertical isothermal surface have been carried out using a parallel CFD code SMAFS (Smoke Movement And Flame Spread) developed by the first author to study the dynamics of the natural convection flow and the associated convective heat transfer, with sub-grid scale turbulence modeled using the Smagorinsky model. In the computation, the filtered governing equations are discretized using finite volume method, with the variables at the cell faces in the finite volume discrete equations approximated by a second order bounded QUICK scheme and the diffusion term computed based on central difference scheme. The computation was time marched explicitly, with momentum equations solved based on a second order fractional-step Adams-Bashford scheme and enthalpy computed using a second order Runge-Kutta scheme. The Poisson equation for pressure from the continuity equation was solved using a multi-grid solver. The results including the temperature and velocity profiles of the boundary layer and the local heat transfer rate are analyzed. Comparison is made with experimental data and good agreement is found.
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| 19. |
- Yan, Zhenghua
(författare)
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Large eddy simulations of a turbulent thermal plume
- 2007
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Ingår i: Heat and Mass Transfer. - : Springer Science and Business Media LLC. - 1432-1181 .- 0947-7411. ; 43:6, s. 503-514
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Tidskriftsartikel (refereegranskat)abstract
- Large eddy simulations of a three-dimensional turbulent thermal plume in an open environment have been carried out using a self-developed parallel computational fluid dynamics code SMAFS (smoke movement and flame spread) to study the thermal plume's dynamics including its puffing, self-preserving and air entrainment. In the simulation, the sub-grid stress was modeled using both the standard Smagorinsky and the buoyancy modified Smagorinsky models, which were compared. The sub-grid scale (SGS) scalar flux in the filtered enthalpy transport equation was modeled based on a simple gradient transport hypothesis with constant SGS Prandtl number. The effect of the Smagorinsky model constant and the SGS Prandtl number were examined. The computation results were compared with experimental measurements, thermal plume theory and empirical correlations, showing good agreement. It is found that both the buoyancy modification and the SGS turbulent Prandtl number have little influence on simulation. However, the SGS model constant C (s) has a significant effect on the prediction of plume spreading, although it does not affect much the prediction of puffing.
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| 20. |
- Yan, Zhenghua, et al.
(författare)
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Numerical investigations of rack storage fires
- 1999
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Ingår i: Fire Safety Science. - 0925223255 ; , s. 1075-1086
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A number of numerical simulations of rack storage fires have been carried out, with various fuel types and burner outputs. Both the standard buoyancy-modified k - turbulence model and a recently developed turbulence model which significantly improves the consideration of the buoyancy effect on turbulence and turbulent transport, were used to study the turbulence of the buoyant flow. The flamelet concept, coupled to a prescribed probability density function, was employed to model the non-premixed combustion process. Sooting was modeled by solving the balance equations for mass fraction and number density considering nucleation, surface growth, coagulation and oxidation. The discrete transfer method was used to calculate radiation, with the radiation properties of the main radiating species - carbon dioxide, water vapour and soot, provided by a fast, narrowband model. The results, including heat flux and gas temperature profile, were analyzed and compared with experimental measurements. The comparisons showed considerably improved agreement for the new model. Copyright International Association for Fire Safety Science.
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| 21. |
- Yan, Zhenghua
(författare)
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Numerical Modeling of Turbulent Combustion and Flame Spread
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Theoretical models have been developed to address several important aspects of numerical modeling of turbulent combustion and flame spread. The developed models include a pyrolysis model for charring and non-charring solid materials, a fast narrow band radiation property evaluation model (FASTNB) and a turbulence model for buoyant flow and flame. In the pyrolysis model, a completely new algorithm has been proposed, where a moving dual mesh concept was developed and implemented. With this new concept, it provides proper spatial resolution for both temperature and density and automatically considers the regression of the surface of the non-charring solid material during its pyrolysis. It is simple, very efficient and applicable to both charring and non-charring materials. FASTNB speeds up significantly the evaluation of narrow band spectral radiation properties and thus provides a potential of applying narrow band model in numerical simulations of practical turbulent combustion. The turbulence model was developed to improve the consideration of buoyancy effect on turbulence and turbulent transport. It was found to be simple, promising and numerically stable. It has been tested against both plane and axisymmetric thermal plumes and an axisymmetric buoyant diffusion flame. When compared with the widely used standard buoyancy-modified model, it gives significant improvement on numerical results. These developed models have been fully incorporated into CFD (Computational Fluid Dynamics) code and coupled with other CFD sub-models, including the DT (Discrete Transfer) radiation model, EDC (Eddy Dissipation Concept) combustion model, flamelet combustion model, various soot models and transpired wall function. Comprehensive numerical simulations have been carried out to study soot formation and oxidation in turbulent buoyant diffusion flames, flame heat transfer and flame spread in fires. The gas temperature and velocity, soot volume fraction, wall surface temperature, char depth, radiation and convection heat fluxes, and heat release rate were calculated and compared with experimental measurements. In addition, to provide comprehensive data for comparison, experiments on room corner fire growth were undertaken, where the gas temperature, solid fuel surface temperature, radiative heat flux, char depth and heat release rate were all measured.
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| 22. |
- Yan, Zhenghua, et al.
(författare)
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Numerical Prediciton of Heat Flux from Flame in Room Fire
- 1997
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A number of CFD (Computational Fluid Dynamics) calculations were carried out to simulate the large scale room corner fire, which is an important scenario for the evaluation of the fire performance of the surface lining material. Considered are turbulent gas flows, turbulent combustion, radiation and heat conduction inside solid boundary. Heat transfer from flame and hot gas is calculated, with the important radiation component presented by discrete transfer (DT) method and the convection heat transfer considered by the wall function. An absorptivity and emissivity model was employed to predict the radiation property of combustion products including soot, CO2 and H2O, which are usually the primary radiating species in the combustion of hydrocarbon fuels. Configurations are a square burner flame in the corner of the standard full scale fire room, with three different standoff distances: 0 cm, 5 cm and 10 cm, and two different burner outputs: 40 kW and 150 ItW. Totally, six cases were studied. The results, including the temperature and heat fluxes, are discussed and compared with experimental measurements.
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| 23. |
- Yan, Zhenghua
(författare)
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Parallel computation of turbulent combustion and flame spread in fires
- 2002
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Ingår i: Numerical Heat Transfer Part B: Fundamentals. - 1040-7790. ; 39:6, s. 191-208
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Tidskriftsartikel (refereegranskat)abstract
- A parallel procedure based on a single-program, multiple-data (SPMD) algorithm is presented for parallel computing of turbulent combustion and flame spread in fires. The computation is based on modeling of radiative turbulent reacting flow and pyrolysis of solid fuel. With angular domain decomposition applied to the parallel computing of radiation and spatial domain decomposition to the computation of nonradiative turbulent reacting flow and solid fuel pyrolysis, the whole computation is distributed among a group of concurrent tasks, which communicate with each other through a message-passing interface library. Using this procedure, a self-developed computational combustion code has been parallelized on both a multiprocessor PC and a symmetric multiprocessor (SMP) system, SGI Origin 2000. The parallelization was verified by comparing the parallel results with sequential results. The performance of the parallel procedure was evaluated using various test cases. As expected, the efficiency of parallelism varies with both computer architecture and case scenario. In general, good efficiency was obtained.
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| 24. |
- Yan, Zhenghua, et al.
(författare)
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Three-dimensional computation of heat transfer from flames between vertical parallel walls
- 1999
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Ingår i: Combustion and Flame. - 0010-2180. ; 117:3, s. 574-588
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Tidskriftsartikel (refereegranskat)abstract
- The heat transfer from turbulent diffusion flames between vertical walls has been computed for different wall and burner configurations. The buoyancy-modified k- model was used to study the turbulent characteristics of the flow. The flamelet concept, coupled to a prescribed probability density function, was employed to model the nonpremixed combustion process. With the nucleation, surface growth, coagulation, and oxidation considered, sooting was modeled by solving the balance equations for mass fraction and number density. The radiation from the main radiating species - carbon dioxide, water vapor and soot - was calculated using the discrete transfer method. A recently developed fast, narrow-band model was adopted to provide the radiation properties of the radiating species. Computations were performed for different cases by varying the wall separation and burner output. The results were analyzed and compared with experimental measurements, with which they showed good agreement. The effects of wall separation and burner output on heat transfer were faithfully reproduced.
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| 25. |
- Yan, Zhenghua, et al.
(författare)
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Validation of CFD Model for Simulation of Spontaneous Ignition in Bio-mass Fuel Storage
- 2005
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Ingår i: [Host publication title missing].
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Konferensbidrag (refereegranskat)abstract
- Both numerical simulations and experimental measurements of small scale spontaneous ignition with different biomass fuels have been performed. In the experiments, temperature history was monitored at five different locations inside the fuel bed. The measured temperature history was used for validation of comprehensive threedimensional computer simulations which were carried out using a parallel finite volume CFD code SMAFS (Smoke Movement and Flame Spread) developed by the first author. The computation was based on numerical solution of a set of governing equations including the continuity equation, extended Darcy momentum equations, energy conservation equations for both gas and solid phases, and mass conservation equations for different chemical species. With reliable material properties input data provided by separate measurements, it simulated the temporal state evolution inside the biomass fuel storage. In the simulation, consideration was given to a series of essential physical and chemical processes, including convection and diffusion in porous media, evaporation, condensation and heat generation which is mainly due to chemical oxidation. Numerical results were compared with experimental measurements, showing excellent agreement.
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