Abstract
Numerical simulations are performed on a combustor setup which represents the recirculating behaviour of a combustor in the flameless combustion regime. Previous experimental and numerical studies showed that heat loss is prominent for this setup. Here, the amount of heat loss through the combustor walls is quantified and its effect analysed. For this a non-adiabatic Flamelet Generated Manifold (FGM) model is employed. This model uses tabulated chemistry in combination with governing equations for a small set of control variables to accurately describe a turbulent flame. In the current implementation, equations for enthalpy and the mean and variance of the reaction progress variable are solved. Turbulence-chemistry interactions are incorporated through a presumed-PDF approach. In contrast to earlier work, the model is applied in the commercial solver Ansys CFX, coupled to a low-mach, compressible, steady-state Reynolds-Averaged Navier-Stokes (RANS) turbulence model. Results from the simulations show that heat loss consumes over 30% of the combustor’s thermal power. Despite this large heat loss, its effect on the combustion chemistry is small. The inclusion of heat loss in the chemistry tabulation does improve the prediction of the velocity and temperature field in the primary reaction zone. However, the effect of including heat loss is limited in the prediction of species concentrations.
Highlights
In view of reducing emissions, development of combustors in the flameless combustion regime is an interesting topic
The Flamelet Generated Manifold (FGM) model combines two concepts in the modelling of turbulent combustion: (1) the reduction of the chemistry based on the reaction time scales and (2) the assumption that combustion occurs in the flamelet regime, (i.e., Da 1, Ka < 1)
The flamelet generated manifold as described in the previous sections is stored as a database
Summary
In view of reducing emissions, development of combustors in the flameless combustion regime is an interesting topic. View [1] for an overview of experimental rigs reported in literature One of such setups is the FLOX® type of combustors, developed at the German Aerospace Centre (DLR), see Lammel et al [2]. Proch and Kempf [10] proposed a heat release dampening factor, which reduces the RPV and enthalpy source terms to emulate the effect of heat loss The results of this method show similar behaviour to the method of multiple flamelets at different enthalpy levels. The effect of several forms of heat loss on this configuration was studied using non-adiabatic chemistry tabulation and a conjugate heat transfer approach for the wall temperature The latter improved the prediction of the flame dynamics only marginally.
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