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Assessment of implementation variants of conditional scalar dissipation rate in LES-CMC simulation of auto-ignition of hydrogen jet

Tyliszczak A.

Archives of Mechanics

2013

Vol. 65, nr 2

97-129

In this paper the large eddy simulation (LES) and conditional moment closure (CMC) combustion model have been applied for modelling of auto-ignition of hydrogen jet issuing into a hot ambient co-flow. Most of the attention was devoted to modelling aspects of the conditional scalar dissipation rate which is a key quantity of the CMC model. Two models are compared with emphasis on differences in distributions in mixture fraction space. Analysis of mutual relations between the terms of CMC equations confirms importance of the conditional scalar dissipation rate. It is also shown that model constants are crucial from the point of view of an auto-ignition location and a flame lift off height. The numerical results are compared with experimental data and both the mean and the root mean square fluctuating values of the temperature and species mass fraction agree well with measurements.

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

Marazioti P., Koutmos P.

Engineering Transactions

2009

Vol. 57, iss. 3/4

127-144

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.