This paper is devoted to analyze the special class of turbulent premixed ames that we call intermediate steady propagation (ISP) ames. These ames are common to industrial premixed combustion chambers which operate at intensive turbulence when velocity pulsations are signi cantly higher than the amelet combustion velocity. They are characterized by a practically constant turbulent combustion velocity, controlled by turbulence, chemistry and molecular processes, and by an increasing ame width, controlled mainly by turbulent di usion.The main content of this work is a description of physical backgrounds and outcome of the original asymptotical (i.e., valid at high Re and Da numbers) premixed combustion model, that, from a methodological point of view, is close to Kolmogorov analysis of developed turbulence at high Re numbers. Our analysis starts from the thickened and strongly wrinkled amelets combustion mechanism. Quantitative results for this model are based on the Kolmogorov assumption of the equilibrium ne-scale turbulence and on additional assumption of the universal small-scale structure of the wrinkled amelet sheet. From this background it is possible to deduce formulas for the thickened amelets parameters and the amelet sheet area and hence the turbulent combustion velocity of the premixed ame. These formulas are used for the closure of the combustion equation written in terms of a progress variable leading to the so called turbulent ame closure (TFC) model for the numerical simulation of ISP ames. Consistent to the ISP ames, in this work the concept of countergradient transport phenomenon in premixed combustion is analyzed.

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Theoretical background, details of implementation, and validation results for a computational model for turbulent premixed gaseous combustion at high turbulent Reynolds numbers are presented. The model describes the combustion process in terms of a single transport equation for a progress variable; turbulent closure of the progress variable’s source term is based on a model for the turbulent flame speed. The latter is identified as a parameter of prime significance in premixed turbulent combustion and determined from theoretical considerations and scaling arguments, taking into account physico-chemical properties and local turbulent parameters of the combustible mixture. Specifically, phenomena like thickening, wrinkling, and straining of the flame front by the turbulent velocity field are considered, yielding a closed form expression for the turbulent flame speed that involves, e.g., speed, thickness, and critical gradient of a laminar flame, local turbulent length scale, and fluctuation intensity. This closure approach is very efficient and elegant, as it requires only one transport equation more than the non reacting flow case, and there is no need for costly evaluation of chemical source terms or integration over probability density functions. The model was implemented in a finite-volume-based computational fluid dynamics code and validated against detailed experimental data taken from a large-scale atmospheric gas turbine burner test stand. The predictions of the model compare well with the available experimental results. It has been observed that the model is significantly more robust and computationally efficient than other combustion models. This attribute makes the model particularly interesting for applications to large three-dimensional problems in complicated geometries.

. In this case earlier work suggests that turbulent premixed ames have increasing ame brush width controlled in the model only by turbulence and independent from the counter-gradient transport phenomenon which has gasdynamics nature, and a turbulent ame speed which quickly adapts to a local equilibrium value, i.e. Intermediate Steady Propagation (ISP) ames. According to the present analysis transport in turbulent premixed ames is in fact composed by two contributions: real physical gradient turbulent di usion, which is responsible for the growth of ame brush thickness, and counter-gradient pressure-driven convective transport related to the di erential acceleration of burnt and unburnt gases subject to the average pressure variation across the turbulent ame. The novel gas dynamics model for the pressuredriven transport which is developed here, shows that in open turbulent premixed ames the overall transport may be of gradient or counter-gradient nature according to which of these two contributions is dominant and that along the ame a transformation from gradient to counter-gradient transport takes place. Reasonable agreement with the mentioned laboratory experimental data, strongly support the validity of the present modelling ideas. Finally, the model predicts existence of this phenomenon also in large-scale industrial burners at much higher Reynolds numbers.

Theoretical background, details of implementation and validation results of a computational model for turbulent premixed gaseous combustion at high turbulent Reynolds numbers are presented. The model describes the combustion process in terms of a single transport equation for a progress variable; closure of the progress variable’s source term is based on a model for the turbulent flame speed. The latter is identified as a parameter of prime significance in premixed turbulent combustion and is determined from theoretical considerations and scaling arguments, taking into account physico-chemical properties of the combustible mixture and local turbulent parameters. Specifically, phenomena like thickening, wrinkling and straining of the flame front by the turbulent velocity field are considered, yielding a closed form expression for the turbulent flame speed that involves, e.g., speed, thickness and critical gradient of a laminar flame, local turbulent length scale and fluctuation intensity. This closure approach is very efficient and elegant, as it requires only one transport equation more than the non-reacting flow case, and there is no need for costly evaluation of chemical source terms or integration over probability density functions. The model was implemented in a finite-volume based computational fluid dynamics code and validated against detailed experimental data taken from a large scale atmospheric gas turbine burner test stand. The predictions of the model compare well with the available experimental results. It has been observed that the model is significantly more robust and computationally efficient than other combustion models. This attribute makes the model particularly interesting for applications to large 3D problems in complicated geometries.