FY2019-000200-CT: Relative Impact of Convective vs. Radiative Heat Loading in Gas Turbine Combustors

Increasing engine performance and thermal efficiency can be achieved through increasing combustor firing temperature. Increasing temperature can also result in durability issues for the combustor hardware, including surface burning, thermal stresses, and accelerated component degradation. Prediction of these durability issues is difficult, however, as combustor flow fields are complex and computational fluid dynamics (CFD) predictions often do not properly capturethe multi-physics nature of combustion. Predictions of heat flux to the combustor wall, and hence wall temperatures, are often inaccurate for three reasons. First, typical combustion simulation does not account for thermal radiation with sufficient fidelity; the distinctively different radiative characteristics of the condensed phase (soot) and the gas phase at elevated pressures is challenging for models to capture. Second, turbulent wall models developed for turbulent flows do not account for many critical physical processes in combustors, including chemical reactions and variable density and viscosity, which results in uncertainties in the prediction of convective heat flux. Third,the transient behavior of combustion systems has been given very little treatment in the literature but could be a significant driver of thermal stress on combustor liner components. In this situation, its not just liner temperature, but the heat flux variation rate that drives material degradation. It is for these reasons that a better physical understanding of how turbulent combustion processes drive combustor liner heat transfer is critical to the Navys goals of higher performance jet engines.There are three goals of the proposed work. First, use tightly-integrated experiments and simulations to quantify the relative contributions of radiation vs. convection on wall hea models through parametric comparison among models and between modelsand experiments. Third, quantify the impact of transient heat loading on the thermal state of the combustor liner for a range of different transient timescales. In the proposed program, experiment and simulation will work in close concert to address the three goals of the project. The project is divided into four tasks, eac that state-of-the-art models are correctly capturing physical processes occurring inside the combustor. Each task adds a layer of complexity, starting with non-reacting, non-radiating flow to understand convective heat transfer, then progressively adding more physics to understand the relative contribution of each to wall heattransfer: radiative heat transfer in non-reacting environments, transient radiative loading, and finally radiative and convective heat transfer with a flame present.The results of the propos will allow the Navy to better understand potentially damaging processes in mission-critical components, including gas turbine main combustors and augmentors.The data and analyses proposed here will provide engineers with enhanced understanding of complex combustion phenomena to better diagnose issues with engines in the field, interpret combustor simulations, and develop engineering solutions for improving the performance and durability of the gas turbine fleet. On the fundamental side, this work will provide much neededcontext for the work in the gas turbine heat transfer community on combustor liner heat transfer in the absence of combustion. These studies are critical, as they provide high-resolution data and new modeling strategies, but it is important to understand the extent of their applicability and the role that the flame plays in both convective and radiative heat transfer to the liner.