A. Maltsev

Numerical Study of the Precessing Vortex Core in a Confined Partially Premixed Swirl Combustion System

Swirl flows play an important role in modern combustion systems such as gas turbines, aero propulsion systems etc. Next to desirable effects such as enhanced mixing such flows often exhibit aerodynamical instabilities called precessing vortex core. The configuration under study here represents a model Gas Turbine(GT) combustion chamber and features the main properties of real gas turbine combustors: a confined swirled flow with multiple recirculation zones and reattachment points, resulting in reacting case in a partially premixed methane/air aerodynamically stabilised flame. This flame exibits also precessing vortex core (PVC). The present study especially concentrates on an evaluation of the performance of different URANS-based model-combinations in predicting this confined swirling reacting flow exhibiting such aerodynamic instabilities. For this purpose an extended Bray-Moss-Libby model and a G-equation based approach, both coupled to the mixture fraction transport equation to account for partially premixed effects, are applied. Their prediction potential in capturing partially premixed combustion properties is appraised by comparison with LDV, Raman and PLIF measurements. It turns out that the influence of the combustion model on simulation results of the flame front stabilisation or mean flow field is not obvious. Nevertheless it could be mentioned that the computation time with G-equation was approximately three times longer than with BML model due to the reinitialization needed in steady case calculations and 2 times longer in case of unsteady calculations.© 2007 ASME

A new BML-based RANS modelling for the description of gas turbine typical combustion processes

The work is concentrated on the formulation and validation of integral models within RANS framework for the numerical prediction of the premixed and partially premixed flames occurring in gas turbine combustors. The premixed combustion modelling is based on the BML approach coupled to the mixing transport providing variable equivalence ratio. Chemistry is described by means of ILDM model solving transport equations for reaction progress variables conditioned on the flame front. Multivariate presumed PDF model is used for the turbulence-chemistry interaction treatment. Turbulence is modelled using the second moment closure (SMC) and the standard κ-e model as well. The influence of non-gradient turbulent transport is investigated comparing the gradient diffusion closure and the solution of the scalar flux transport equations. Different model combinations are assessed simulating several premixed and partially premixed flame configurations and comparing results to the experimental data. The proposed model provides good predictions particularly in combination with SMC.

Numerical Prediction of Partially Premixed Flames Based on Extended BML Model Coupled With Mixing Transport and ILDM Chemical Model

To improve the numerical prediction of partially premixed flames occurring in gas turbine combustors the extension of the well-known Bray-Moss-Libby model for premixed combustion is presented. The model modification based on the algebraic closure for a mean chemical source term is coupled to the mixing transport model providing variable equivalence ratio distinguishing partially premixed flames. Finite rate chemistry is incorporated by means of ILDM model solving transport equations for two reaction progress variables conditioned on the flame front. Multivariate presumed PDF model is used for the turbulence chemistry interaction treatment. Turbulence models of two levels of complexity are applied in order to investigate the influence of non-gradient turbulent transport phenomenon. Redistribution terms in second moment transport equations are extended to take into account strongly variable density effects. Model combinations considered are assessed simulating piloted partially premixed flame. The obtained results agree well with experimental data.Copyright