Application of the Unified Turbulent Flame-Speed Closure (UTFC) Combustion Model to Numerical Computation of Turbulent G
The current work presents the numerical computation of turbulent reactive flow by means of three different classes of flame: a premixed, a non-premixed and a partially premixed flame. The aim thereby is to validate the unified turbulent flame-speed closur
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Abstract The current work presents the numerical computation of turbulent reactive flow by means of three different classes of flame: a premixed, a non-premixed and a partially premixed flame. The aim thereby is to validate the unified turbulent flame-speed closure (UTFC) combustion model developed at our institute. It is based on the presumption that the entire turbulent flame can be viewed as a collection of laminar premixed reaction zones (flamelets) with different mixing ratios. The mixing process is controlled by the mixture fraction and the subsequent chemical reaction by the progress variable . The turbulent flame speed St is used to describe the flame/turbulence interaction as well as the finite rate reaction. Complex chemistry is included and the pressure dependency (elevated pressure) of the combustion process is included in the model as well. The applicability of the model is explored by means of RANS (Reynolds averaged Navier-Stokes approach) and LES (large eddy simulation) methodologies at a wide range of Damk¨ohler number Da. The results of all simulations show reasonable good agreement with the experiments.
1 Introduction CFD (computational fluid dynamics) simulation of combustion systems is an important and reliable tool in designing and optimizing combustion devices like combustion engines or gas turbines. For such industrial flows with high Reynolds number Re, the resolution of all turbulent scales and the computation of all reacting species concentrations is not possible due to computational costs. For this reason, modeling is needed to simplify the underlying physics, namely: turbulence
F. Zhang () P. Habisreuther H. Bockhorn Division of Combustion Technology, Engler-Bunte-Institute, Karlsruhe Institute of Technology, Engler-Bunte-Ring 1, 76131 Karlsruhe, Germany e-mail: [email protected] W.E. Nagel et al. (eds.), High Performance Computing in Science and Engineering ’12, DOI 10.1007/978-3-642-33374-3 16, © Springer-Verlag Berlin Heidelberg 2013
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and combustion. Since combustion occurs in complex 3D flows characterized by high turbulence intensities and thermal loads in industrial applications, the turbulent length scales are in the order of the typical laminar flame thickness ıl , suggesting that the flamelet assumptions [1] are in most cases violated. Proper and comprehensive modeling therefore becomes important and is the objective of the work. There are numerous modeling concepts for turbulent combustion which usually underly different physical restrictions, for example, some are only applicable for premixed or non-premixed flames or for fast chemistry. For turbulence modeling, the classical RANS method is fast, but provides only information about the time mean variables of the flow and lack transient characteristics. On the other hand, the LES offers the possibility to resolve the unsteady flow structures down to a cut-off level and therefore is a good compromise between computational costs and additional accuracy. The main difficulty for LES modelin
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