Large eddy simulation of hydrogen-air propagating flames

The future use of hydrogen as a clean fuel and an energy carrier brings in safety issues that have to be addressed before community acceptance can be achieved. In this regard, availability of accurate modeling techniques is very useful. This paper presents large eddy simulations (LES) of propagating turbulent premixed flames of hydrogen-air mixtures in a laboratory scale combustion chamber. A Dynamic flame surface density (DFSD) model where the reaction rate is coupled with the fractal analysis of the flame front structure, is implemented and tested. The fractal dimension is evaluated dynamically based on the instantaneous flow field. The main focus of the current work is to establish the LES technique as a good numerical tool to calculate turbulent premixed hydrogen flames having an equivalence ratio of 0.7. Developing this capability has practical importance in analyzing explosion hazards, internal combustion engines and gas turbine combustors. The results obtained with the DFSD model are compare well with published experimental data. Further investigations are planned to examine and validate the LES-DFSD model for different flow geometries with hydrogen combustion

Numerical experiments of hydrogen-air premixed flames

Numerical experiments have been carried out to study turbulent premixed flames of hydrogen-air mixtures in a small scale combustion chamber. Flow is calculated using the Large Eddy Simulation (LES) Technique for turbulent flow. The chemical reaction is modeled using a dynamic procedure for the calculation of the flame/flow interactions. Sensitivity of the results obtained to the computational grid, ignition source and different flow configurations have been carried out. Numerical results are validated against published experimental data. It was found that the grid resolution has very small effect on the results after a certain grid. Also, the ignition source has influenced only the time where the peak overpressure appears. Finally, the different configurations are reported to affect both the peak overpressure and flame position

Large eddy simulation of hydrogen-air premixed flames in a small scale combustion chamber

While hydrogen is attractive as a clean fuel, it poses a significant risk due to its highreactivity. This paper presents Large Eddy Simulations (LES) of turbulent premixed flames of hydrogeneair mixtures propagating in a small scale combustion chamber. The sub-grid-scale model for reaction rate uses a dynamic procedure for calculating the flame/ flow interactions. Sensitivity of the results to the ignition source and to different flow configurations is examined. Using the relevant parameter from the calculations, the flames are located on the regimes of combustion and are found to span the thin and corrugated flamelet regimes, hence confirming the validity of flamelet modelling. The calculations are compared to published experimental data for a similar configuration. It is found that both the peak overpressure and flame position are affected by the number of baffles positioned in the path of the flame and this is consistent with earlier findings for hydrocarbon fuels. Also, the LES technique is able to reproduce the same flame shape as the experimental images. A coarse study of sensitivity to the ignition source shows that the size of the ignition kernel does not affect the flame structure but influences only the time where the peak overpressure appears while moving the ignition source away from the base plate leads to a decrease in the peak overpressure