Effect of mainstream forced entrainment on the combustion performance of a gas turbine combustor

In trapped vortex combustors, a radial strut is designed to improve the combustion efficiency and achieve uniform temperature distribution. However, under the action of the strut, a mainstream forced entrainment phenomenon may take place in the cavity, which would extinguish the local flame there. In this study, to achieve high combustion efficiency with robust stability, a strategy to optimize the radial strut was proposed to control the mainstream forced entrainment phenomenon. Then, an experimental study was conducted to investigate the effects of mainstream forced entrainment on the combustion efficiency, ignition, and lean blowout performance in a workable trapped vortex combustor. Additionally, numerical simulations on the flow field were performed to obtain insights into the experimental results. It was found that the mainstream entrained into the cavity is helpful for improving the combustion efficiency and inner-cavity ignition performance. This occurs because the entrained mainstream changes the flow field behind the strut, which provides many more shield regions for fuel combustion and flame propagation. However, the mainstream entrained into the cavity is harmful to the ignition of the outer cavity and lean blowout performance, because the entrained mainstream can not only decrease the size of the main vortex of the cavity, but also reduce the local fuel to air ratio inside the cavity. Additionally, it was found that a change in the strut dimensionless parameter L/D can effectively control the flow fields, and thus the combustion performance. Furthermore, a critical value of 0.50 was obtained for the strut dimensionless parameter L/D.