Geometrical Parametric Studies of Inter Turbine Burner (ITB) for Improved Performance

Abstract

Three-dimensional CFD simulations were conducted in order to determine the performance of UltraCompact-Combustor (UCC) configurations proposed for use as an Inter-Turbine Burner (ITB) in aerospace gas turbine propulsion systems. Previous work has shown that a UCC/ITB concept recently developed by AFRL has shown promise. In this study, six design modifications designed to enhance vorticity generation, promote mixing in the top circumferential cavity, and to enhance the entrainment of combustion products from the circular cavity into the main stream more flow have been proposed. Vorticity producing ramps have been effectively used to enhance mixing in high speed combustion systems. This idea has been utilized to propose three modifications to the side wall and one to the top wall of the circumferential cavity (CC) of the baseline concept. These modifications have the desirable characteristic of introducing very little blockage to the CC flow. A swirler like geometry placed on the side wall of the CC has also been proposed. In addition, variation of the fuel injection angle has studied. These modifications are intended to drive radial transport of combustion products from the CC into the main airflow and promote lean burning. The CFD results indicate that the performance of the UCC/ITB is not dependent upon the shape of the CC side wall vorticity enhancers. In fact the three side wall concepts had very little overall impact on the flow. Intense burning in the ITB CC was predicted by the CFD simulations, suggesting strong flame stability characteristics, improved lean blowout performance, and high combustion efficiency of the AFRL UCC/ITB concept. The results further showed that the location of the vorticity enhancers, to some extent plays an important role in determining the migration mechanism and shedding rate of the combustion products from the high g-loaded swirling CC into the main airflow producing distinct burning patterns downstream of the Radial Vane Cavities (RCV) trailing edge. These burning patterns, however, were found to produce somewhat unconventional radial temperature and fuel-air ratio profiles at the ITB exit plane. These radial profiles indicate an increased need for mixing of combustion products with main airflow, even with the enhancers. The results generally indicate that the exit temperature profile is quite insensitive to vortex enhancers located on side plates, but sensitive to the vorticity enhancer located on the top wall of the CC, due to the centrifugal effects of the injection air into the circumferential cavity and the resulting high G effects. It appears that the ITB exit profile can be manipulated by placing suitable devices on the top wall to produce disturbances into the CC flowfield. Therefore, this study indicates a need for further design, CFD, and experimental efforts to improve main air stream and combustion products mixing performance.