Abstract

One of the consequences of increasing the efficiency of gas turbine combustors is the higher combustion temperatures within the chamber. Advances on managing larger heat loads have been made to protect the combustor wall and turbines. Among those are thermal barrier coatings (TBCs) deposited on metal walls and forced air cooling such as through effusion holes. Historically, both the flame and TBCs have received a simplified gray treatment using effective absorptivities and emissivities. However, studies have shown that the gray analysis can considerably under-predict the cold metal side temperature resulting in misguided combustor life estimates. In this study, non-gray radiation is compared to gray and black radiation by combining three-dimensional Monte Carlo Ray Tracing (MCRT) solution of non-gray flames in a model gas turbine combustor to one-dimensional energy balance within combustor liners. A recent large eddy simulation (LES) of a gas turbine combustor is analyzed, where both gray and non-gray models are exercised. A two-band spectral model is employed for the TBC, where a translucent band and an opaque band are identified. A line-by-line treatment for gas-phase radiation is adopted, and the incident radiative energy on the combustor wall is collected using the MCRT solver, where the fraction of radiative energy within the translucent band is collected and compared with those obtained from the blackbody assumption. The temperature distributions along the multi-layered combustor wall are computed and parametric comparison is conducted. The effects of the nongray flame radiation are more prominent at elevated pressures than at atmospheric pressure, leading to a difference of approximately 150 K in the prediction of peak temperature on the hot side of the TBC. The gray model is found to over-predict the TBC temperature at downstream locations, but under-predict the TBC temperature near the flame locations. The present study proposes a methodology to estimate the wall temperatures when radiation within the TBC is considered. Future work includes application of the methodology to more realistic combustors where both radiative fluxes and convective fluxes can be accurately captured.

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