Experimental and Numerical Investigations of a Low-Pressure Turbine Control Stage

Partial admission occurs in steam turbines operated under part load when one or more segments of the channel annulus are deliberately blocked and thus are not available for the working medium to flow through. This occurrence, common in control stages, is related to strongly unsteady flow conditions, which in turn have heavy repercussions on the machine’s performance and stable range of operation. Therefore, a deeper understanding of the loss generation mechanisms related to partial flow admission is necessary for a flexible and reliable machine design, stable part load operation and advanced steam turbine blades. In this study, combined numerical and experimental investigations of the flow in a low - speed axial turbine have been conducted to highlight some of the relevant features of partial flow admission. Using experimental 2D flow field traverse data, a detailed characterization of the flow field in full admission has been carried out in order to validate the experimental technique and the numerical approach. In preparation for further targeted measurements, numerical simulations of the flow in partial admission have been performed and results have been analyzed. T he studies showed that the flow phenomena occurring at partial admission are characterized by increased local gradients regarding the pressure and the velocity field, causing challenges in terms of calibration, positioning and alignment of the probes during the scheduled measurements of partial admission scenarios