Simulation of Hydrogen-Air-Diluents Mixture Combustion in an Acceleration Tube with FlameFoam Solver (original) (raw)
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2002
The design and assessment of hydrogen mitigating systems in a nuclear power plant needs the detailed simulation with high spatial resolution of the major physical processes including hydrogen source terms, distribution, ignition, and combustion, taking into account local gas conditions. The present project in the 4 1 h EU Framework Programmedeals with the development and verification of physical and numerical models that can be used in multidimensional CFD codes, which solve the general equations of reactive fluid dynamics. The objective of the joint research programme was to develop CFD-models for hydrogen distribution, turbulent combustion, and hydrogen mitigation techniques, which can be applied to risk reduction in current and future nuclear power plants. The work programme consisted, firstly, of an experimental part with tests suitable to provide a data base, secondly, of modeling and Validation work, and thirdly, of application of the validated numerical tools to full-scale demonstration cases. In two small scale facilities at the Lehrstuhl A für Thermodynamik, Technical University of Munich (TUM), experiments provided data over a wide range of flame regimes, including the interaction of the flame front with obstacle configurations. A medium scale test facility at the Forschungzentrum Karlsruhe (FZK) provided data on turbulent combustion in the range of medium fast turbulent deflagrations up to detonation velocity. In inert tests, the conditions after a propagating shock wave through an obstacle path were also investigated. In addition, results of large-scale tests performed in the RUT facility at the Kurchatov Institute (KI) have been used for model verification. It was concluded, that incomplete combustion is not possible for dry mixtures with more than 10.5 vol-% hydrogen and that results depend weakly on obstacle spacing. Further, three phases in the combustion process can be distinguished: a slow acceleration phase is followed by a fast one, later the flame propagates with constant velocity in the tubes with repeated obstacles. The numerical tools involved in this project are COM3D and GASFLOW at FZK, REACFLOW at Joint Research Centre Ispra (JRC), TONUS at Commissariat a !'Energie Atomique (CEA) and models implemented in CFX4.2 at TUM. The codes were verified in a two-step approach. Firstly, each code was tested against standard test cases and against different experiments. Secondly, the codes were used to calculate a common set of experiments. These benchmark calculations allowed a direct comparison of the different numerical models and implementations. Model applications were a) TONUS simulation of H2-steam distribution and combustion in four-compartment geometry, b) GASFLOW simulation of the Battelle Helium injection test Hyjet Jx7 and of Batteile recombiner tests GX6 and GX7, c) GASFLOW simulation of H 2-steam distribution with mitigation during a large break LOCA and d) full reactor scale turbulent combustion simulation with COM3D With data from four different facilities, the experimental database, which has been developed within the present project, is unique in its size and completeness. In addition to provide data for the validation of numerical codes, the experiments also provide useful insight into the physical phenomena involved in turbulent combustion processes. The range of applicability of combustion codes used within this project were found tobe complementary to each other. While no single code covers the whole area of interesting combustion regimes, a combination of the different codes can describe the whole combustion process from ignition over the flame acceleration regime to fully developed detonations. Limitations of the present combustion models and need for further Validation do not allow fully quantitative predictions of the detailed containment Ioads under all conditions. However, they allow studies of the 5 Model application
Multi-dimensional simulation of hydrogen distribution and turbulent combustion in severe accidents
Nuclear Engineering and Design, 2001
The design and assessment of hydrogen mitigating systems in a nuclear power plant needs the detailed simulation with high spatial resolution of the major physical processes including hydrogen source terms, distribution, ignition, and combustion, taking into account local gas conditions. The present project in the 4 1 h EU Framework Programmedeals with the development and verification of physical and numerical models that can be used in multidimensional CFD codes, which solve the general equations of reactive fluid dynamics. The objective of the joint research programme was to develop CFD-models for hydrogen distribution, turbulent combustion, and hydrogen mitigation techniques, which can be applied to risk reduction in current and future nuclear power plants. The work programme consisted, firstly, of an experimental part with tests suitable to provide a data base, secondly, of modeling and Validation work, and thirdly, of application of the validated numerical tools to full-scale demonstration cases. In two small scale facilities at the Lehrstuhl A für Thermodynamik, Technical University of Munich (TUM), experiments provided data over a wide range of flame regimes, including the interaction of the flame front with obstacle configurations. A medium scale test facility at the Forschungzentrum Karlsruhe (FZK) provided data on turbulent combustion in the range of medium fast turbulent deflagrations up to detonation velocity. In inert tests, the conditions after a propagating shock wave through an obstacle path were also investigated. In addition, results of large-scale tests performed in the RUT facility at the Kurchatov Institute (KI) have been used for model verification. It was concluded, that incomplete combustion is not possible for dry mixtures with more than 10.5 vol-% hydrogen and that results depend weakly on obstacle spacing. Further, three phases in the combustion process can be distinguished: a slow acceleration phase is followed by a fast one, later the flame propagates with constant velocity in the tubes with repeated obstacles. The numerical tools involved in this project are COM3D and GASFLOW at FZK, REACFLOW at Joint Research Centre Ispra (JRC), TONUS at Commissariat a !'Energie Atomique (CEA) and models implemented in CFX4.2 at TUM. The codes were verified in a two-step approach. Firstly, each code was tested against standard test cases and against different experiments. Secondly, the codes were used to calculate a common set of experiments. These benchmark calculations allowed a direct comparison of the different numerical models and implementations. Model applications were a) TONUS simulation of H2-steam distribution and combustion in four-compartment geometry, b) GASFLOW simulation of the Battelle Helium injection test Hyjet Jx7 and of Batteile recombiner tests GX6 and GX7, c) GASFLOW simulation of H 2-steam distribution with mitigation during a large break LOCA and d) full reactor scale turbulent combustion simulation with COM3D With data from four different facilities, the experimental database, which has been developed within the present project, is unique in its size and completeness. In addition to provide data for the validation of numerical codes, the experiments also provide useful insight into the physical phenomena involved in turbulent combustion processes. The range of applicability of combustion codes used within this project were found tobe complementary to each other. While no single code covers the whole area of interesting combustion regimes, a combination of the different codes can describe the whole combustion process from ignition over the flame acceleration regime to fully developed detonations. Limitations of the present combustion models and need for further Validation do not allow fully quantitative predictions of the detailed containment Ioads under all conditions. However, they allow studies of the 5 Model application
International Journal of Hydrogen Energy, 2014
A numerical approach has been developed to simulate flame acceleration and deflagration to detonation transition in hydrogen-air mixture. Fully compressible, multidimensional, transient, reactive NaviereStokes equations are solved with a chemical reaction mechanism which is tuned to simulate different stages of flame propagation and acceleration from a laminar flame to a turbulent flame and subsequent transition from deflagration to detonation. Since the numerical approach must simulate both deflagrations and detonations correctly, it is initially tested to verify the accuracy of the predicted flame temperature and velocity as well as detonation pressure, velocity and cell size. The model is then used to simulate flame acceleration (FA) and transition from deflagration to detonation (DDT) in a 2-D rectangular channel with 0.08 m height and 2 m length which is filled with obstacles to reproduce the experimental results of Teodorczyk et al. The simulations are carried out using two different initial ignition strengths to investigate the effects and the results are evaluated against the observations and measurements of Teodorczyk et al.
2020
Korea Atomic Energy Research Institute (KAERI) established a multi-dimensional hydrogen analysis system to evaluate a hydrogen release, distribution, and combustion in the containment of a nuclear power plant using MAAP, GASFLOW, and COM3D. KAERI developed the COM3D analysis methodology on the basis of the COM3D validation results against the experiments of ENACCEF and THAI. The proposed analysis methodology accurately predicts the peak overpressure with an error range of approximately ±10% using the Kawanabe turbulent flame speed model. KAERI performed a hydrogen flame acceleration analysis using the multi-dimensional hydrogen analysis system for a severe accident initiated by a station blackout (SBO) under the assumption of 100% metal-water reaction in the reactor pressure vessel for evaluating an overpressure buildup in the Advanced Power Reactor 1400 MWe (APR1400). The COM3D calculation results using the established analysis methodology showed that the calculated peak pressure i...
Simulation of turbulent explosion of hydrogen–air mixtures
International Journal of Hydrogen Energy, 2014
Spherically expanding turbulent premixed hydrogen-air flames are computed using the Reynolds-Averaged Navier-Stokes (RANS) approach. The mean reaction rate is modelled using unstrained and strained flamelets, and an algebraic model. Since the temperature and mass fraction evolve differently in hydrogen flames because of non-unity Lewis numbers, two reaction progress variables are used in the calculations. The computed turbulent burning velocity is compared to measured values to validate the computational models.
Experimental and numerical investigations of hydrogen jet fire in a vented compartment
International Journal of Hydrogen Energy, 2018
Hydrogen fires may pose serious safety issues in vented compartments of nuclear reactor containment and fuel cell systems under hypothetical accidents. Experimental studies on vented hydrogen fires have been performed with the HYKA test facility at Karlsruhe Institute of Technology (KIT) within Work Package 4 (WP4)-hydrogen jet fire in a confined space of the European HyIndoor project. It has been observed that heat losses of the combustion products can significantly affect the combustion regimes of hydrogen fire as well as the pressure and thermal loads on the confinement structures. Dynamics of turbulent hydrogen jet fire in a vented enclosure was investigated using the CFD code GASFLOW-MPI. Effects of heat losses, including convective heat transfer, steam condensation and thermal radiation, have been studied. The unsteady characteristics of hydrogen jet fires can be successfully captured when the heat transfer mechanisms are considered. Both initial pressure peak and pressure decay were very well predicted compared to the experimental data. A pulsating process of flame extinction due to the consumption of oxygen and then self-ignition due to the inflow of fresh air was captured as well. However, in the adiabatic case without considering the heat loss effects, the pressure and temperature were considerably over-predicted and the major physical phenomena occurring in the combustion enclosure were not able to be reproduced while showing large discrepancies from the experimental observations. The effect of sustained hydrogen release on the jet fire dynamics was also investigated. It indicates that heat losses can have important implications and should be considered in hydrogen combustion simulations.
Numerical modeling of hydrogen diffusion jet flame: the role of the combustion model
The prediction of turbulent reactive flows largely depends on the proper choice of a combustion model. The closure of the highly non linear production term in the species conservation equation is one of the most challenging aspects when modeling turbulent combustion with RANS/FANS approaches. The main value of the species reaction rates cannot be obtained by simply substituting the mean variables into the Arrhenius equations, and the effects of turbulence on temperature and species concentration fields must be taken into account. Several approaches have been proposed in the literature to provide a proper modelling of mean reaction rates. The Eddy Dissipation Model is based on the infinitely fast chemistry hypothesis and assumes that the reaction rate is controlled by turbulent mixing . A generalized formulation of the Eddy Dissipation Model, i.e. EDM/FR, has been proposed in order to take into account finite rate chemistry effects, however, this model is not suited to treat detailed combustion mechanisms and fails with a number of reactions larger than three or four. The Eddy Dissipation Concept (EDC) is an extension of EDM which allows detailed kinetics to be included in the calculations . The model assumes that chemical reactions occur within the smallest turbulent structures, called fine structures. These are treated as perfectly stirred reactors (PSR) which exchange mass with the surrounding fluid. The overall reaction rate in each PSR is controlled by chemical kinetics. The properties of the fine structures are derived from a step-wise energy cascade model and expressed with quantities related to the main flow, such as the turbulent kinetic energy, k, and the turbulent dissipation rate, _. Two formulations of EDC have been developed, for fast and finite rate chemistry respectively [2]. Both combustion models described above are based on the reaction rate approach. A different approach is based on the primitive variable and originates a group of combustion models. In its simplest formulation, this approach allows the decoupling of chemistry and flow field calculation. The chemical reaction rates are computed off-line and stored in lookup tables, accessible by the flow solver. The instantaneous variables are expressed in terms of mixture fraction and enthalpy and, then, integrated over an assumed _-PDF probability density function to get the mean scalar variables. In the Flamelet approach, the flame is modelled as an ensemble of thin and steady laminar flames, strained by the turbulent motion. According to this model, two scalar equations, for the mixture fraction and its variance, have to be solved independently of the number of species involved in the chemical mechanism. The influence of the outer flow field on the inner reaction zone is described by the scalar dissipation rate. This represents a reciprocal residence time within the flame sheets which is increased by stretch effects of turbulence motion and reduced by diffusion. At a critical value of the dissipation rate the flame shows a threshold behaviour and extinguishes. The mean values of scalar properties are computed from the instantaneous values which are integrated over a probability density function with a presumed _-PDF shape. The integration is not carried out during the CFD calculation but is part of the flamelet library generation, in order to reduce the computational cost. The flamelet libraries are created with a mixture fraction ranging between zero and unity and for discrete
Numerical Investigation of Turbulent Hydrogen-Methane-Nitrogen Non-Premixed Jet Flame
Journal of Energy Technologies and Policy, 2016
In this work, the numerical investigation of the two-dimensional axisymmetric turbulent diffusion flame of a composite fuel was performed by using a computational fluid dynamics code to predict flame structure. The composite fuel was an H 2 /CH 4 /N 2 gas mixture. The amount of H 2 and N 2 in the fuel mixture varies under constant volumetric fuel flow rate. Fluent, which solves the governing and reaction equations using the finite volume method, was used as the computational fluid dynamics program. The non-premixed model was used for computation of the combustion. The standard k-ε model was used for modeling the turbulent flow. The interaction of the chemistry and turbulence was accounted for by the program with the probability density function model. This model was validated against the experimental data taken from literature. In general, the numerical results of the temperature, velocity, and CO 2 concentration distributions were in satisfactory agreement with the experimental results. The numerical results showed that adding H 2 to the fuel mixture decreases the flame length and generally increases the maximum temperature of the flame. On the other hand, adding N 2 to the mixture decreases both the flame length and maximum flame temperature. The flame length corresponds to the axial position of the peak flame temperature.
Modelling of Lean Uniform and Non-Uniform Hydrogen-Air Mixture Explosions in a Closed Vessel
Simulation of hydrogen-air mixture explosions in a closed large-scale vessel with uniform and nonuniform mixture compositions was performed by the group of partners within the EC funded project "Hydrogen Safety as an Energy Carrier" (HySafe). Several experiments were conducted previously by Whitehouse et al. in a 10.7 m 3 vertically oriented (5.7-m high) cylindrical facility with different hydrogen-air mixture compositions. Two particular experiments were selected for simulation and comparison as a Standard Benchmark Exercise (SBEP) problem: combustion of uniform 12.8% (vol.) hydrogen-air mixture and combustion of non-uniform hydrogen-air mixture with average 12.6% (vol.) hydrogen concentration across the vessel (vertical stratification, 27% vol. hydrogen at the top of the vessel, 2.5% vol. hydrogen at the bottom of the vessel); both mixtures were ignited at the top of the vessel. The paper presents modelling approaches used by the partners, comparison of simulation results against the experiment data and conclusions regarding the non-uniform mixture combustion modelling in real-life applications.
Vented explosion of hydrogen/air mixture: An intercomparison benchmark exercise
International Journal of Hydrogen Energy, 2018
Explosion venting is a widely used mitigation solution in the process industry to protect indoor equipment or buildings from excessive internal pressure caused by accidental explosions. However, vented explosions are very complicated to model using computational fluid dynamics (CFD). In the framework of a French working group, the main target of this investigation is to assess the predictive capabilities of five CFD codes used by five different organizations by means of comparison with recent experimental data. On this basis several recommendations for the CFD modelling of vented explosions are suggested.