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

Abstract

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.

Importance of the vane exit Mach number on the axial clearance-related losses

“…A previous study 12 concluded that there are five main loss sources that are affected by the axial clearance: (1) stator wake mixing with the main flow, (2) unsteady interaction between the stator wake and rotor blade, (3) changing rotor incidence, (4) endwall boundary layer losses and (5) stator trailing edge shock-related losses. The study was able to link four loss sources to the correlating design parameters, leaving only stator trailing edge shock related losses out of the analysis due to a lack of data.…”

“…Maximum linear correlations are plotted as solid lines. It has been suggested that the axial clearance g/c x between 0.35 and 0.42 is a good choice to begin the design process with 12 (area shown between dotted lines). This choice is also close to the common design practices 7 where g/c x is 0.3–0.4.…”

“…This study aims to shed light on the correlations of the remaining two non-dimensional parameters by applying linear correlation analysis used in the previous article 12 and an earlier on by Turunen-Saaresti and Jaatinen. 26 First, the geometry and the numerical method used for the new turbine data are presented.…”

Influence of tip clearance inclination on the performance of axial flow impeller in storage mode

“…The clearance width at different positions is also very important. 26 There are several cases. The first is that the clearance width of the blade leading-edge is relatively wide and that at the trailing-edge is relatively narrow.…”

Loss Assessment of the Axial-Gap Size Effect in a Low-Pressure Turbine

“…Bellucci et al (2017) found a strong interdependency of axial-gap related losses with both aspect ratio and inlet Reynolds number. In a review of the literature, Grönman et al (2014) were able to correlate the axial-gap size effect with secondary parameters like the stator's pitch-toaxial-chord ratio, circumferential Mach number, and the rotor aspect ratio. Additional dependencies, such as the rotor being shrouded or unshrouded, cavity design or blade loading, are likely to exist as well.…”