Gas detonation cell width prediction model based on support vector regression

Detonation cell width is an important parameter in hydrogen explosion assessments. The experimental data on gas detonation are statistically analyzed to establish a universal method to numerically predict detonation cell widths. It is commonly understood that detonation cell width, λ, is highly correlated with the characteristic reaction zone width, δ. Classical parametric regression methods were widely applied in earlier research to build an explicit semiempirical correlation for the ratio of λ/δ. The obtained correlations formulate the dependency of the ratio λ/δ on a dimensionless effective chemical activation energy and a dimensionless temperature of the gas mixture. In this paper, support vector regression (SVR), which is based on nonparametric machine learning, is applied to achieve functions with better fitness to experimental data and more accurate predictions. Furthermore, a third parameter, dimensionless pressure, is considered as an additional independent variable. It is found that three-parameter SVR can significantly improve the performance of the fitting function. Meanwhile, SVR also provides better adaptability and the model functions can be easily renewed when experimental database is updated or new regression parameters are considered

An Intercomparisation of CFD Models to Predict Lean and Non-Uniform Hydrogen Mixture Explosions

The paper describes an exercise on comparison of Computational Fluid Dynamics (CFD) models to predict deflagrations of a lean uniform hydrogen-air mixture and a mixture with hydrogen concentration gradient. The exercise was conducted within the work-package "Standard Benchmark Exercise Problem" of the EC funded Network of Excellence "Hydrogen Safety as an Energy Carrier", which seeks to provide necessary accuracy in the area of applied hydrogen safety simulations. The experiments on hydrogen-air mixture deflagrations in a closed 1.5 m in diameter and 5.7 m high cylindrical vessel were chosen as a benchmark problem to validate CFD codes and combustion models used for prediction of hazards in safety engineering. Simulations of two particular experiments with approximately the same amount of hydrogen were conducted: deflagration of a uniform 12.8% vol. hydrogen mixture and deflagration of a non-uniform hydrogen mixture, corresponding to an average12.6% vol. hydrogen concentration (27% at the top of the vessel, 2.5% at the bottom of the vessel) with ignition at the top of the vessel in both cases. The comparison of the simulation results for pressure and flame dynamics against the experimental data is reported.JRC.F.2-Cleaner energ

An Inter-Comparison Exercise on CFD Model Capabilities to Simulate Hydrogen Deflagrations with Pressure Relief Vents

The comparison between experimental data and simulation results of hydrogen explosions in a vented vessel is described in the paper. The validation exercise was performed in the frame of the European Commission co-funded Network of Excellence HySafe (Hydrogen Safety as an Energy Carrier) that has the objective to facilitate the safe introduction of hydrogen technologies. The mitigation effect of vents on the strength of hydrogen explosions is a relevant issue in hydrogen safety. Experiments on stoichiometric hydrogen deflagrations in a 0.95 m3 vessel with vents of different size (0.2 m2 and 0.3 m2) have been selected in the available scientific literature in order to assess the accuracy of computational tools and models in reproducing experimental data in vented explosions. Five organizations with experience in numerical modelling of gas explosions have participated to the code benchmarking activities with four CFD codes (COM3D, REACFLOW, b0b and FLUENT) and one code based on a mathematical two-zone model (VEX). The numerical features of the different codes and the simulations results are described and compared with the experimental measurements. The agreement between simulations and experiments can be considered satisfactory for the maximum overpressure while correctly capturing some relevant parameters related to the dynamics of the phenomena such as the pressure rise rate and its maximum has been shown to be still an open issue.JRC.F.2-Cleaner energ

Modelling of Lean Uniform and Non-Uniform Hydrogen-Air Mixture Explosions in a Large-Scale Closed Vessel

Simulation of hydrogen-air mixture explosions in a closed large-scale vessel with uniform and non-uniform 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 m3 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.JRC.F.2-Cleaner energ

An Inter-Comparison Exercise on CFD Model Capabilities to Simulate Hydrogen Deflagrations in a Tunnel

In the frame work of the European Commission co-funded Network of Excellence HySafe (Hydrogen Safety as an Energy Carrier, www.hysafe.org), five organizations with significant experience in explosion modelling have performed numerical simulations of explosions of stochiometric hydrogen-air mixtures in a 78.5 m long tunnel. The five organizations are the Karlsruhe Research Centre, GexCon AS, the Joint Research Centre, the Kurchatov Institute Research Centre and the University of Ulster. Five CFD (Computational Fluid Dynamics) codes with different turbulence and combustion models have been used in this Standard Benchmark Exercise Problem (SBEP). Since tunnels are semi-confined environments, hydrogen explosions in tunnels can potentially be critical accident scenarios from the point of view of the accident consequences and CFD methods are increasingly employed to assess explosions hazards in tunnels. The objective of the validation exercise is to assess the accuracy of the theoretical and numerical models by comparisons of the simulation results with the experimental data. The simulation results are presented, analysed and compared to the experimental data. A very good agreement between experiments and simulations was found in terms of maximum overpressures.JRC.F.2-Cleaner energ

An Inter-Comparison Exercise on CFD Model Capabilities to Predict a Hydrogen Explosion in a Simulated Vehicle Refuelling Environment

The paper describes the comparison of simulations of a hydrogen explosion experiment in an environment simulating a vehicle refuelling station. The exercise was performed in 2007 within the European-Commission-funded Network of Excellence Hydrogen Safety as an Energy Carrier (www.hysafe.org), which facilitates the safe introduction of hydrogen technologies and infrastructure. The experiment in a mock-up of a hydrogen refuelling station was conducted jointly by Shell Global Solutions (UK) and the Health and Safety Laboratory (UK) in order to study the potential hazards and consequences associated with a hydrogen-air mixture explosion. The worst-case scenario of a stoichiometric hydrogen-air mixture explosion was offered to the network partners for this simulation exercise. Simulations were conducted by a total of seven partners using different models and numerical codes with the intention of predicting/reproducing pressure dynamics in different locations and of evaluating the performance of different combustion codes and models in realistic large-scale conditions. The paper briefly details the models and numerical codes used, and presents the simulated pressure transients obtained by the partners in comparison with the experimental pressure records. The comparative model analysis was made based on achieved simulation results, where the simulated maximum overpressure and the characteristic rate of pressure rise were treated as major output parameters. A contribution to hydrogen safety was made in the form of a description of the models, their performance and an analysis of the results for their cross-fertilisation where possible.JRC.F.2-Cleaner energ