Loss reduction in a 1.5 stage axial turbine by computer-driven stator hub contouring

2020-03-30T10:34:55Z (GMT) by H Obaida A Rona J Gostelow
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 deliver about 80% of the 20 trillion kWh world-wide electricity. Component-level improvements are therefore timely and important towards achieving carbon dioxide global emission targets. Secondary flow loss reduction is sought by applying a non-axisymmetric 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 (RANS) simulations, which is used to optimize the hub surface. The three-dimensional steady RANS model with an axisymmetric hub is validated against reference experimental measurements from Rheinisch-Westfälische Technische Hochschule Aachen. Comparative computational fluid dynamics predictions with an optimized non-axisymmetric hub show a decrease in the total pressure loss coefficient and an increase in the isentropic stage efficiency at and off design conditions.