Turbulent combustion in a curving, contracting channel with a cavity stabilized flame

Abstract

Thermal analyses of gas turbine engine cycles have shown that energy addition in the turbine stage can provide improvements in specific thrust/power, thrust/power to volume ratios as well as specific fuel combustion. One of the strategies to achieve this energy addition is to have an auxiliary combustion chamber(s) in the transition duct between the turbine stages or in the stator passages of each turbine stage. This type of combustion system is sometimes called a “ Turbine Burner” . To have combustion in high-speed accelerating flows, a low-speed zone has to be created for mixing and flame holding. A cavity was used in this experiment to achieve the low-speed zone. Flame stability and flame holding were investigated in this study. Non-reacting flow tests on the system showed that the cavity was able to entrap a vortex and act as a flame anchor. Temperature measurements showed that the shear layer separating the combustion in the cavity and the cold flow in the main channel acts almost like a wall and reduces thermal transport. The temperature profiles upstream and downstream of the cavity also showed that the temperature was not uniform downstream and the downstream combustion was completely contained in the boundary layer attached to the curving wall. This can be partially attributed to the low density of hot gases and the fact that they stay closer to the inner curve due to high radial g forces. The flame was stable at very low and very high flow rates. In the transition between the above two regimes, the flame was unstable and intermittent. Fourier analysis of the acoustic and combustion frequencies showed that there is little coupling between the heat release rate and acoustic modes of the system.