Aeromechanical Test of a Newly Developed Low-Pressure Section for Variable Speed Application

Abstract Low Pressure stage design characteristics play a key role in steam turbine product line as they typically set limits to the maximum turbine flow and rotating speed and have a strong influence on the overall turbine efficiency. LP stages design presents a combination of structural and aerodynamics challenges that push the manufacturers to develop and test the design well in advance with respect to the turbine design schedule. For the same reason (development complexity) an LP stages design is usually scaled to cover a wide range of rotating speed and annulus area. The set of scaled LP stage is referred to as LP stage family. Variable speed applications typical of mechanical drive steam turbines add further complexity to the design, requiring the blades to be designed to withstand potential fundamental x-rev crossings inside the operating speed range. Author’s company presented in 2023 a paper describing all the phases of the development of a new LP family for mechanical drive applications, named MS (Medium Speed), starting from aerodynamic design to mechanical integrity verification, to manufacturing and assembly. This paper will present the last step of the design phase, prior to field application, that is aeromechanical validation test, that has been carried out for the MS8 size as representative of the entire LP family. The aeromechanical validation of MS8 has been carried out in a full-scale rotating test in a vacuum chamber (so called wheel Box Test, WBT), by means of high velocity oil jets impinging onto the blades. During the tests the 2-stage rotors frequencies and damping were measured with a system of strain gages and no contact probes. Aim of the present paper is to present an overview of the experimental activity and post-processed data.