The performance of a 1.5 stage axial turbine with a non-axisymmetric casing at off-design conditions

Advances in manufacturing techniques allow greater freedom in designing axial turbine stage passages, including non-axisymmetric end walls. A non-axisymmetric end wall design method for the stator casing is implemented through a novel surface definition, towards mitigating secondary flow losses. The new design is compared with a diffusion design from the literature. Off-design operations are considered. Numerical predictions of a 1.5 stage axial turbine show a reduction in the rotor row total pressure loss of 1.69 % against the benchmark axisymmetric stage from RTWH Aachen, which is validated against experiment. Flow analysis gives an insight into the effectiveness of the new surface definition approach, which is implemented using Alstom Process and Optimization Workbench (APOW) software at design conditions. The numerical predictions show that performance is retained at off-design conditions.