Influence of the axial turbine design parameters on the stator–rotor axial clearance losses

The drive towards lower emissions in aerospace engines promotes more efficient and physically smaller engines. One way to decrease the size of the axial turbine is to minimize the distance between successive stator and rotor rows. This can usually have either a positive or negative influence on the turbine performance. The reasons for this behaviour are not currently fully understood. In this study, a novel approach is taken to find new insights into this design question by analysing the influence of different design parameters on the turbine efficiency behaviour. Several different turbines are analysed using the literature. For the first time, the performed analysis reveals the design parameters, which correlate with the different efficiency curve shapes. The correlating parameters are the stator–rotor axial clearance, stator pitch to axial chord ratio, turning velocity Mach number and rotor aspect ratio. The mechanisms behind the found correlations are further analysed to connect the physical phenomena with the design parameters.