Performance of Annular Combustor-Dump Diffusers

In this paper results of an experimental investiga- tion of the performance of an annular combustor-dump diffuser are presented. The geometry comprised a straight -walled pre -diffuser followed by a sudden expan - sion in which the flow divides and passes to the two con - centric annuli surrounding the flame tube. Tests were carried out to investigate the influence of: pre -diffuser geometry, the distance between pre -diffuser outlet and the head of the flame tube and, the division of flow between the two concentric annuli. The system is shown to offer good performance and flow stability over a wide range of operating conditions. The way in which the presence of the flame tube improves the performance and stability of flow in the pre-diffuser is demonstrated. Whereas nearly all of the pressure rise occurs in the pre-diffuser most of the total pressure loss occurs near the head of the flame tube. Minimum total pressure loss and a symmetrical pressure distribution on the head of the flame tube was obtained with a symmetrical velocity profile at pre-diffuser outlet. The results also focus attention on the need to carefully match the geometries of the pre -diffuser, flame tube and surrounding annuli. Nomenclature