The Effect of Partial Premixing and Heat Loss on the Reacting Flow Field Prediction of a Swirl Stabilized Gas Turbine Model Combustor

Abstract

This work addresses the prediction of the reacting flow field in a swirl stabilized gas turbine model combustor using large-eddy simulation. The modeling of the combustion chemistry is based on laminar premixed flamelets and the effect of turbulence-chemistry interaction is considered by a presumed shape probability density function. The prediction capabilities of the presented combustion model for perfectly premixed and partially premixed conditions are demonstrated. The effect of partial premixing for the prediction of the reacting flow field is assessed by comparison of a perfectly premixed and partially premixed simulation. Even though significant mixture fraction fluctuations are observed, only small impact of the non-perfect premixing is found on the flow field and flame dynamics. Subsequently, the effect of heat loss to the walls is assessed assuming perfectly premixing. The adiabatic baseline case is compared to heat loss simulations with adiabatic and non-adiabatic chemistry tabulation. The results highlight the importance of considering the effect of heat loss on the chemical kinetics for an accurate prediction of the flow features. Both heat loss simulations significantly improve the temperature prediction, but the non-adiabatic chemistry tabulation is required to accurately capture the chemical composition in the reacting layers.

Keywords: Heat loss effects; Partial premixing; Tabulated chemistry; Turbulent combustion.

Fig. 1

Source term of reaction progress variable ${\tilde{S}}_c\left[\frac{\text{kg}}{{\mathrm{m}}^3\mathrm{s}}\right]$ as function of mean and variance of reaction progress $\tilde{c}$

Fig. 2

Source term of unscaled reaction progress variable ${\omega }_{Y_c}\left[\frac{\text{kg}}{{\text{m}}^3\text{s}}\right]$ as function of mixture fraction f and unscaled progress variable Y _c for non-premixed, adiabatic conditions

Fig. 3

Source term of reaction progress variable $S_c\left[\frac{\text{kg}}{{\text{m}}^3\text{s}}\right]$ for perfectly premixed, non-adiabatic conditions

Fig. 4

Sketch of one half of the burner as used in the numerical simulations. It includes plenum, swirler and combustion chamber with the main dimensions. The air and fuel inlets are visualized by arrows. The flame location is indicated and the inner and outer recirculation zones are marked

Fig. 5

Cut through the computational domain showing the computational mesh for the premixed case with close up views of the different refinement regions in the combustion chamber and swirler section

Fig. 6

Isosurface of stoichiometric mixture fraction f _st = 0.055 colored by the time averaged velocity magnitude for ϕ = 0.83

Fig. 7

Instantaneous iso-contours of axial velocity colored by temperature. The different time instances are t = 0.0868 s (top), t = 0.0992 s (middle) and t = 0.1116 s (bottom). The results correspond to the partially premixed conditions with ϕ = 0.83

Fig. 8

Comparison of time-averaged fields for perfectly premixed and partially premixed simulation. Dashed lines indicate the measurement stations for comparison with the experimental data

Fig. 9

Mean axial velocity (top) and RMS profiles (bottom): Experiments (), perfectly premixed simulation () and partially premixed simulation ()

Fig. 10

Mean radial velocity (top) and RMS profiles (bottom): Experiments (), perfectly premixed simulation () and partially premixed simulation ()

Fig. 11

Mean transversal velocity (top) and RMS profiles (bottom): Experiments (), perfectly premixed simulation () and partially premixed simulation ()

Fig. 12

Mean mixture fraction (top) and RMS profiles (bottom): Experiments (), perfectly premixed baseline case () and partially premixed simulation (). Note that the mixture fraction is not explicitly used in the perfectly premixed simulation and the respective profile is only added as a reference

Fig. 13

Mean temperature (top) and RMS profiles (bottom): Experiments (), perfectly premixed () and partially premixed simulation ()

Fig. 14

Scatter plot at h = 6 mm above the burner exit. The global mixture fraction and the adiabatic flame temperature are marked. The IRZ and ORZ are indicated in the scatter plot based on the experimental data

Fig. 15

Flame index computed from Y _f and Y _O using the partially premixed turbulent combustion model

Fig. 16

Mean fields for adiabatic (left) and heat loss simulation (right)

Fig. 17

Mean temperature (top) and RMS profiles (bottom): Experiments (), perfectly premixed, adiabatic simulation (), perfectly premixed, non-adiabatic simulation in which the chemistry is not affected by heat loss (), perfectly premixed, non-adiabatic simulation () and perfectly premixed, non-adiabatic simulation including radiative heat transfer ()

Fig. 18

CH₄ mass fractions. Experiments (), perfectly premixed, adiabatic simulation (), perfectly premixed, non-adiabatic simulation in which the chemistry is not affected by heat loss (), perfectly premixed, non-adiabatic simulation (), perfectly premixed, non-adiabatic simulation including radiative heat transfer ( ) and non-premixed simulation ()

Fig. 19

CO Mass fraction. Experiments (), perfectly premixed, adiabatic simulation (), perfectly premixed, non-adiabatic simulation in which the chemistry is not affected by heat loss (), perfectly premixed, non-adiabatic simulation (), perfectly premixed, non-adiabatic simulation including radiative heat transfer () and partially premixed simulation ()

Fig. 20

Comparison of OH-LIF measurements [4] (left) with the OH concentrations of the adiabatic simulation (middle) and the non-adiabatic simulation (right)