Aerodynamic performance analysis of partial admission dual row control stage at different working conditions

Aerodynamic performance of partial admission dual row control stage at the rated and off-designed operating conditions was numerically investigated using three-dimensional Reynolds-averaged Navier-Stokes (RANS) and k -ε turbulence model. The full scale computational model includes the four nozzle boxes, full first and second row rotor blade, as well as two admission guided vanes with consideration of the rotor tip clearance and stator diaphragm gland. The numerical results of the mass flow rate, power output and aerodynamic efficiency of the dual row control stage at the rated and off-designed conditions are well in agreement with the experimental data. The obtained results at rated condition show that the blocking segmental arc of guided vane increased the exit pressure of the upstream nozzle, which reduced the mass flow rate and changed the aerodynamic performance of the nozzle. The circumferential non-uniformity of aerodynamic parameters and partial admission losses increases with the decrease in the admission degree for the computed three operating conditions. The analysis of axial steam velocity shows that the trailing shedding vortex and the complex flow vortex in flow passages have a significant impact on the magnitude and direction of the axial steam velocity. Furthermore, the partial admission degree changed the proportions of the power output of two rotor blade rows. The lower partial admission degree leads to a larger proportion of the power output of the first rotating blade row. The detailed flow pattern in the partial admissions dual row control stage at different operating conditions is also illustrated.