Supersonic Flow Behavior in Cartridge Starter

Hot flow analysis was undertaken in a cartridge starter using NUMECA software. Cartridge starter provides high temperature gases with kinetic energy which impinges on to the rotor blades of the turbine at the initial stage of starting a gas turbine engine which sets gas turbine to rotate. Other starting mechanisms which can be used are air starter, electric motor or a small gas turbine engine. The cartridge starter assembly consists of gas generator section with perforated central core, vertical tube/pipe which bifurcates into two pipe lines, called short arm and long arm, which provide high velocity hot gases to the high pressure turbine rotor blades. These two pipelines form convergent–divergent nozzles. Computational fluid dynamics (CFD) analyses were carried out for nine operating points for the inlet pressure ranging from 90 to 157 bar. Analyses considered the cartridge starter gas flow domain only and burning model is not considered. Hexahedral cells are generated with cut cell approach using fine Hexpress software. The problem is considered as three-dimensional, steady, compressible with turbulent flow for the flow analysis. The aim of the project is to determine the mass flow rate, its distribution in two arms and the total pressure loss. Spalart–Allmaras turbulence model with extended wall function was chosen for this analysis. First analysis showed that the flow was unsteady at the exit plane of nozzle. Therefore, analysis was carried out by considering unsteadiness in the flow and averaged quantities are derived. Flow is found to diffuse in the divergent nozzle after a normal shock. Mass flow rate has reduced due to the formation of shock. It is also found that the total pressure loss has reduced near the perforated central core of cartridge starter.