Operation of industrial steam turbines under partial admission is usually implemented in order to cope with fluctuations in demand while maintaining a high efficiency. Subject of the article presented is the experimental investigation of the performance and efficiency of a control stage operated with air, under partial admission. Furthermore, the steady state blade loading distribution on the stator in a free passage and at the entry into a not admitted passage is observed.
For the experiment, the single-staged axial-flow turbine is operated with varying shaft speed, pressure ratio and admission rate, realized by flow blockaging. Two rotationally symmetric stator endwall designs are tested: a plane and a contoured endwall.
Reducing the admission rate at part load decreases the efficiency, especially at high circumferential velocities as precedent investigations showed. Pumping and mixing loss behaviour shows a different scale across the performance map. To prove CFD Simulations, results of the blade loading distribution on the stator are acquired.