Joint scalar PDF simulations of a bluff-body stabilised flame with the REDIM approach

Transported joint scalar probability density function (PDF) results are presented for ‘Sydney Flame HM3’, a jet type turbulent flame with strong turbulence – chemistry interaction, stabilized behind a bluff body. We apply the novel Reaction-Diffusion Manifold (REDIM) technique, by which a detailed chemistry mechanism is reduced, including diffusion effects. Only N2 and CO2 mass fractions are used as reduced coordinates. A second-moment closure RANS turbulence model is applied. As micro-mixing model, the modified Curl’s coalescence/dispersion (CD) and the Euclidean Minimum Spanning Tree (EMST) models are used. In physical space, agreement between experimental data and simulation results is good up to the neck zone, for the unconditional mean values of velocity, mixture fraction, major and some minor chemical species. Conditional mean profiles in mixture fraction space are also in reasonable agreement with experiments up to the neck zone, though conditional fluctuations tend to be under-predicted. CD generally yields better predictions for the level of fluctuations in mixture fraction space than EMST, but this is partly due to unrealistic particle evolution in composition space. In general, simulations using the REDIM approach for reduction of detailed C2-chemistry confirm earlier findings for micro-mixing model behaviour, obtained with C1-chemistry

Effective algorithm of analysis of integrability via the Ziglin's method

In this paper we continue the description of the possibilities to use numerical simulations for mathematically rigorous computer assisted analysis of integrability of dynamical systems. We sketch some of the algebraic methods of studying the integrability and present a constructive algorithm issued from the Ziglin's approach. We provide some examples of successful applications of the constructed algorithm to physical systems.Comment: a figure added, version accepted to JDC

Generalised langevin model in correspondence with a chosen standard scalar-flux second-moment closure

In the context of transported joint velocity-scalar probability density function methods, the correspondence between Generalised Langevin Models (GLM) for Lagrangian particle velocity evolution and Eulerian Reynolds-stress turbulence models has been established in the 1990's by S.B. Pope. It was shown that the GLM representation of a given Reynolds stress model is not unique. It was also shown that a given GLM together with a given mixing model for particle composition evolution implies a differential scalar-flux model. In this paper, we study how extra constraints can be applied on the choice of the GLM coefficients in order to imply a chosen scalar-flux model. This correspondence between GLM-implied and standard scalar-flux models is based on the linear relaxation term and on the mean velocity gradient contributions in the rapid term. In general, GLM-implied models possibly involve more terms (including anisotropy effects in the scalar-flux decay rate and some high-order terms in the rapid-pressure-scrambling term). The proposed form of the GLM supposes a non-constant value for the diffusion coefficient C (0), originally identified as a Kolmogorov constant. Here, the value of C (0) is determined in order to yield the Monin model for linear relaxation of the scalar-flux, and the constant in the rapid-pressure contribution is related to the choice of the parameter beta (auaEuro parts per thousand) in the GLM. We finally show how GLM-implied scalar-flux models are in general dependent on the choice of the mixing model and how the proposed GLM can reduce this dependency. These developments are illustrated by results obtained from calculations of the Sydney bluff-body stabilised flame HM1

Numerical investigation towards a HiTAC condition in a 9MW heavy fuel-oil boiler

In this study, several conditions in a 9 MW heavy fuel-oil boiler were numerically studied in order to get a better understanding of the application of HiTAC in such a boiler. Simulations were done with an Euler- Lagrange approach. The Eddy Dissipation model was used for combustion. Simulation results showed that by recycling various ratios of flue gas into the primary and secondary air, a more uniform temperature distribution can be achieved. Besides, thermal NOX can be reduced to a lower level. Radiation from soot has shown to have a considerable influence on the predicted temperature profiles. It can reduce the peak temperature by 140 K in the case with hot combustion air