Stator conditioning effects on steam turbine rotating instability

Rotating stall and rotating instability (as it is often called) have been extensively studied in compressors and fan stages. Though less known, they are relevant to steam turbines operated at very low mass flow conditions. In the present work, flow under various flow rate conditions in the last stage of steam turbine configurations is investigated. The objective of this study is to identify the main physical dependent parameters of rotating instability for turbine configurations and to see if they can be used to explore the potential of delaying rotating instability by blading design or by control. The computational results clearly show that the onset and development of the flow instability in the rotor row are subject to the intra-row gap distance and in particular can be influenced by the upstream stator flow conditioning. Further 3D calculations with a re-staggered stator row are carried out to examine the effect on a 3D steam turbine blading configuration. Under the flow conditions considered in this ...