Predictions of Flow and Heat Transfer in Low Emission Combustors

Abstract

Flow and heat transfer predictions in modern low emission combustors are critical to maintaining the liner wall at reasonable temperatures. This study is the first to focus on a critical issue for combustor design. The objective of this paper is to understand the effect of different swirl angle for a dry low emission (DLE) combustor on flow and heat transfer distributions. This paper provides the effect of fuel nozzle swirl angle on velocity distributions, temperature, and surface heat transfer coefficients. A simple test model is investigated with flow through fuel nozzles without reactive flow. The fuel nozzle angle is varied to obtain different swirl conditions inside the combustor. The effect of flow Reynolds number and swirl number are investigated using FLUENT. Different RANS-based turbulence models are tested to determine the ability of these models to predict the swirling flow. For comparison, different turbulence models such as standard k − ε, realizable k − ε, and shear stress transport (SST) k − ω turbulence model were studied for non-reactive flow conditions. The results show that, for a high degree swirl flow, the SST k −ω model can provide more reasonable predictions for recirculation and high velocity gradients. With increasing swirl angle, the average surface heat transfer coefficient increases while the average static temperature will decrease. Preliminary analysis shows that the k − ω model is the best model for predicting swirling flows. Also critical is the effect of the swirling flows on the liner wall heat transfer. The strength and magnitude of the swirl determines the local heat transfer maxima location. This location needs to be cooled more effectively by various cooling schemes.

Comparative Investigation on Heated Swirling Jets Using Experimental and Numerical Computations

“…Note that the convection and production terms are exact, while the remaining terms have to be modeled [27]. Detailed derivations for the closure equations can be found in references [28][29][30][31][32], among others.…”

Multiphysics Simulations of Entrained Flow Gasification. Part I: Validating the Nonreacting Flow Solver and the Particle Turbulent Dispersion Model

“…Although many studies report the superiority of the SST k –ω model in predicting reacting turbulent swirling flows, − the exact physical reason behind its success has yet not been highlighted. We propose the following hypothesis for explaining the success of the SST k –ω in predicting vortex breakdown in swirling flows.…”

“…The k –ω model is a two-equation turbulence model, based on eddy viscosity formulation similar to the k –ε models, but with ε replaced by the quantity ω, which is analogous to ε/ k . A version this model, called the shear stress transport (SST) k –ω model, which blends the standard k –ε and the k –ω models in appropriate regions, has been frequently and successfully applied in the analysis of problems involving swirling and shearing flows, − especially in simulations of gas turbine combustors. − Because of its good performance in the authors’ “preliminary investigations” of turbulent swirling free-jets, the SST model has also been employed to simulate combustion of baled biomass . The SST model was also shown to perform better than the standard and the RNG k –ε models and the realizable k –ε model in swirling flow situations .…”