Numerical investigation of turbulent combustion in a reverse flow combustor using les

Investigation of turbulent combustion is very important for gas turbine design. Although achieving low emission gas turbine operation through turbulent mixing, interaction between turbulence and combustion can affect the performance in terms of stability. With today's supercomputers and numerical methods, this situation can be modeled and overcome without the need for an experimental environment. Large eddy simulation (LES) technique is one of the most powerful computational fluid dynamics (CFD) method if the detailed investigation is intended about turbulent combustion. In terms of gas turbine design, stagnation point reverse flow (SPRF) combustor offers a stable and efficient combustion process resulting from its unique geometry. The presence of the inlet and outlet ports on the same geometrical plane provides internal gas recirculation within the geometry. This feature also reveals a complex flow field. In this study, turbulent combustion interaction in a SPRF combustor is numerically investigated using LES methodology. First, the non-reacting cold flow case is modeled with incompressible LES flow solver. Results showed that LES with one equation sub-grid modeling provided sufficient resolution to capture complex flow field and validate experimental results of the cold flow cases. Further analysis are extended to reacting cases as premixed and non-premixed operations. In the non-premixed operation, a lifted flame is located about the two-thirds of the combustor, while an attached flame is observerd for the premixed operation. Results of the complex flow field and combustion dynamics showed that it can operate at low emission conditions. The existence of the shear layer between the coaxial jets resulted with intense mixing which further increases the efficiency of the combustor. Exhaust gas re-circulation prevented high temperature levels, hence high NOx levels within the combustor. Preliminary thermo-acoustic study showed that noise level are highly affected by the turbulent production and heat release generation. The contribution of the combustion noise to the total noise level is obtained higher in the non-premixed operation as compared to the premixed one. In the non-premixed operation larger heat release is observed. A detailed examination of thermo-acoustic instabilities is necessary to understand its behavior in situations where more power is required. It is also important to test different combustion and reaction mechanisms in order to achieve comparable results. These are targeted as part of future work.