An investigation on flame structure and NOx formation in a gas turbine model combustor using large eddy simulation

Abstract

In this work, large eddy simulations (LES) of a Gas Turbine Model Combustor (GTMC) are done using a five-step global mechanism that includes separate thermal and non-thermal NOx formation parts. To verify the accuracy of the solution, time-averaged profiles of the flow variables and fluctuations are compared to the available experimental and numerical data. The LES results show that the vortical structures inside the chamber are highly connected to the temperature field and chemical reactions, and despite having a major role in fast premixing and consequent NOx reductions, they contribute to NOx generation by forming high temperature spots inclusive of chemical radicals. Also, the importance of the baroclinic torque in vorticity creation is demonstrated by comparing the corresponding values to vortex stretching in upstream parts of the chamber. It is shown that the baroclinic torque mostly takes action between high vorticity and high strain regions and can possibly intensify the strong vortices, while the vortex stretching is mostly active near the strong vortices. Furthermore, observation of detailed statistics shows that most of the heat release occurs in samples with mixture fractions near the global value, while NO generation is highly biased toward the strong vortices and the stoichiometric mixture fraction. To investigate the role of the radicals in more details, a chemical reactor network (CRN) is created by clustering the LES solution. Also, the integration of Partially Stirred Reactors (PaSRs) with Perfectly Stirred Reactor (PSR) networks is used to improve the accuracy of predicting the reactant jet penetration and ignition radicals.

Improved efficiency with concave cavities on S3 surface of a rim-driven thruster

“…To perform the convergence analysis, a procedure called grid convergence index (GCI) based on the Richardson extrapolation method 26,27 has been evaluated by numerous CFD simulations. [28][29][30][31][32] Detailed information on this procedure can be found in Celik et al 33 The results of the assessments are listed in Table V. The data in Table V show that the numerical uncertainties based on the fine-grid solution should be reported as 1.00% and 1.73% for the total thrust and torque acting on the rotor, respectively, implying that our simulations are reliable.…”