Turbulent Flame Visualization Using Direct Numerical Simulation

Article type: Research Article

Authors: Shalaby, H. | Janiga, G. | Laverdant, A. | Thévenin, D.

Affiliations: Laboratory of Fluid Dynamics and Technical Flows, University of Magdeburg "Otto von Guericke", Universitaetsplatz 2, 39106 Magdeburg, Germany. E-mail: Dominique.Thevenin@vst.uni-magdeburg.de | Office National d'Etudes et de Recherches Aérospatiales (ONERA), 29, avenue de la Division Leclerc, BP 72, 92322 Châtillon-sous-Bagneux, France

Abstract: Combustion phenomena are of high scientific and technological interest, in particular for energy generation and transportation systems. Direct Numerical Simulations (DNS) have become an essential and well established research tool to investigate the structure of turbulent flames, since they do not rely on any approximate turbulence models. In this work two complementary DNS codes are employed to investigate different types of fuels and flame configurations. The code π^3 is a 3-dimensional DNS code using a low-Mach number approximation. Chemistry is described through a tabulation, using two coordinates to enter a database constructed for example with 29 species and 141 reactions for methane combustion. It is used here to investigate the growth of a turbulent premixed flame in a methane-air mixture (Case 1). The second code, Sider is an explicit three-dimensional DNS code solving the fully compressible reactive Navier-Stokes equations, where the chemical processes are computed using a complete reaction scheme, taking into account accurate diffusion properties. It is used here to compute a hydrogen/air turbulent diffusion flame (Case 2), considering 9 chemical species and 38 chemical reactions. For Case 1, a perfectly spherical laminar flame kernel is initialized at the center of a cubic domain at zero velocity. A field of synthetic homogeneous isotropic turbulence is then superposed and the turbulent flow and the flame can begin to interact. Various species can be used as an indicator for the flame front in a combustion process. Among them, the isosurface of species CO_2 at a mass fraction of 0.03 is retained here, since this value corresponds to the steepest temperature gradient in the associated one-dimensional laminar premixed flame. The results obtained have been post processed in order to study the interesting aspects of the coupling between flame kernel evolution and turbulence, such as straining and curvature impact on the flame surface area and local thickness. For Case 2, the instantaneous structure of a non-premixed hydrogen/air flame evolving in a turbulent flow and starting from an initially planar structure is investigated. Here again, the properties of the resulting turbulent flame are of high interest and will be visualized, defining the flame front in a classical manner for non-premixed combustion using a mixture fraction isosurface. Considering the context of this publication, the emphasis is clearly set on the post-processing and visualization of the DNS data, not on the fundamental issues associated with turbulent combustion.

Keywords: Direct Numerical Simulation, Turbulent Flames, Visualization, Post-Processing

Journal: Journal of Visualization, vol. 10, no. 2, pp. 187-195, 2007