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1

Simulations of combustion roar in turbulent attached and lifted turbulent methane jet flames

Marazioti P., Koutmos P.

Engineering Transactions

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2009

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Vol. 57, iss. 3/4

127-144

EN

The present work presents sample results of preliminary computations of the turbulent aerothermodynamic flow field and of the noise generated by the flame front, due to turbulent fluctuations in the flame (combustion roar). in lifted and attached jet diffusion flames of methane. The two-dimensional (2D) time-dependent numerical model was built based on Reynolds-averaged Navier Stokes (N-S) equations. eąuipped with the standard k-e turbulence models to calculate the reacting jet flows. A reactedness inixture fraction two-scalar ex-ponential PDF model, based on non-premixed flame arguments. was combined with a local Damkohler number extinction criterion to delineate between the reacting and non-reacting regions. Althougli the inclusion of the effects of premixed flame propagation could help to improve the model, initial comparisons with experimental results suggest adequate qualitative agreemenl between the computations and reported data. The reasonable agreement obtained for the aerothermodynamic flame characteristics permitted a meaningful computation of the combustion noise (roar) characteristics of the studied flames, in order to address the coupled effects of heat release by the flame and turbulent interactions on the autonomous flame noise generation.

2

A global oxidation scheme for propane-air combustion suitable for use into complex reacting flow computations

Koutmos P., Giannakis G., Marazioti P.

Engineering Transactions

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2007

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Vol. 55, iss. 4

293-316

EN

In Direct or Semi-Direct Numerical Simulations of turbulent reacting flows the exploitation of complex, realistic and detailed chemistry and transport models often results in prohibitive memory and CPU requirements when flows of practical relevance are treated. The integrated Combustion Chemistry approach has recently been put forward as a methodology suitable for the integration of complex chemical kinetic and chemistry effects into large scale computational procedures for the calculation of complex and practical reacting flow configurations. Through this procedure, a reduced chemical kinetic scheme involving only a limited number of species and reactions is derived from a detailed chemical mechanism, so as to include major species and pollutants of interest in the main flow calculation. The chemical parameters employed in this integrated scheme i.e. rates, constants, exponents are then calibrated on the basis of a number of constraints and by comparing computations over a range of carefully selected laminar flames so as to match a rumber of prespecified flame properties such as adiabatic temperatures, selected target species profiles, flame speeds, extinction characteristcs. The present work describes such an effort for a commonly used fuel of both the fundamental and practical importance that often is used to simulate the performance of higher hydrocarbons in practical engine simulations, i.e. propane. The proposed nine-step scheme involves nine major stable species and in addition to the basic propane oxidation modei also includes NOx production and soot formation submodels.

3

A reduced multi-step integrated oxidation scheme for methane suitable for use into complex reactive flow calculations

Koutmos P., Dimopoulos S.

Computer Assisted Mechanics and Engineering Sciences

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2005

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Vol. 12, No. 1

17-30

EN

In Direct or Semi-Direct Numerical Simulations of turbulent reacting flows the exploitation of complex, realistic and detailed chemistry and transport models often results in prohibitive memory and CPU requirements when flows of practical relevance are treated. The integrated Combustion Chemistry approach has recently been put forward as a methodology suitable for the integration of complex chemical kinetic and chemistry effects into large scale computational procedures for the calculation of complex and practical reacting flow configurations. Through this procedure a reduced chemical kinetic scheme involving only a limited number of species and reactions is derived from a detailed chemical mechanism so as to include major species and pollutants of interest in the main flow calculation. The chemical parameters employed in this integrated scheme i.e. rates, constants, exponents are then calibrated on the basis of a number of constraints and by comparing computations over a range of carefully selected laminar flames so as to match a number of prespecified flame properties such as adiabatic temperatures, selected target species profiles, flame speeds, extinction characteristics. The present work describes such an effort for a commonly used fuel of both fundamental and practical importance, methane. The proposed nine-step scheme involves nine major stable species and in addition to the basic methane oxidation model also includes NOx production and soot formation submodels.

4

A reactedness model for local extinction and reignition phenomena in turbulent jet diffusion flames

Koutmos P., Mavridis C

Computer Assisted Mechanics and Engineering Sciences

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1999

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Vol. 6, No. 1

115-130

EN

An approach for modeling finite-rate chemistry effects such as local extinction and reignition in piloted diffusion flames of CO/H2/N2 or CH4 and air is presented. A partial equilibrium/two-scalar exponential PDF combustion model is combined with a 2D Large Eddy Simulation procedure employing an anisotropic subgrid eddy-viscosity and two equations for the subgrid scale turbulent kinetic and scalar energies. Statistical independence of tge PDF scalars is avoided and the required moments are obtained from an extended scale-similarity assumption. Extinction is accounted for by comparing the local Damkohler number against a 'critical' local limit related to the Gibson scalar scale and the reaction zone thickness. The post-extinction regime is modelled via a Lagrangian transport equation for a reactedness progress variable that follows a linear deterministic relaxation to its mean value (IEM). Comparisons between simulations and measurements suggested the ability of the method to calculate adequately the partal extinction and reignition phenomena observed in the experiments.