Loss Reduction in a 1.5 Stage Axial Turbine by Computer- Driven Stator Hub Contouring

Improvements in stage isentropic efficiency and reductions in total pressure loss are
sought in a 1.5 stage axial turbine. This is representative of power generation equipment
used in thermal power cycles, which delivers about 80% of the 201012 kWh worldwide
electricity. Component-level improvements are therefore timely and important
toward achieving carbon dioxide global emission targets. Secondary flow loss reduction
is sought by applying a nonaxisymmetric endwall design to the turbine stator hub. A
guide groove directs the pressure side branch of the horseshoe vortex away from the airfoil
suction side, using a parametric endwall hub surface, which is defined as to obtain
first-order smooth boundary connections to the remainder of the passage geometry. This
delays the onset of the passage vortex and reduces its associated loss. The Automatic
Process and Optimization WORKBENCH (APOW) generates a Kriging surrogate model from a
set of Reynolds-averaged Navier–Stokes simulations, which is used to optimize the hub
surface. The three-dimensional steady Reynolds-averaged Navier–Stokes model with an
axisymmetric hub is validated against reference experimental measurements from the
Rheinisch-Westf€alische Technische Hochschule (RWTH) Aachen. Comparative computational
fluid dynamics (CFD) predictions with an optimized nonaxisymmetric hub show a
decrease in the total pressure loss coefficient and an increase in the isentropic stage
efficiency at and off design conditions.