To meet today’s and future market needs, large end-stage blades are obliqued to fulfill high flexibility regarding the operational range and high efficiency goals while being prepared for daily start-stop cycles.The end stage total efficiency can be maximized by enlarging the steam turbine exit area and thereby reducing the exhaust losses. Therefore, a new 2-stage LP backend featuring an increased free-standing 41’’ steel blade is developed and presented here, which is optimized for maximum efficiency and minimal aerodynamic excitations.To allow for such a large steel-blade to operate at 60Hz rotational speed and to meet the cycling demands of daily cycling, all aspects of the blade design are optimized. A new high strength blade steel was developed, see [1], which gives the designer freedom for aerodynamical optimizations, while keeping the mechanical utilization within the predefined limits. To maximize the speed-cycling capability a new four lug fir tree root has been developed which minimizes the static as well as the dynamic loading. To verify the success of the root-shape optimization and to verify the frequency tuning of the first six tuned modes, an extensive validation measurement campaign was set-up in a full-scale testing facility under vacuum. Here, the airfoil, root and steeple of the last stage blade were equipped with static as well as dynamic strain gauges. Additionally, the blade row was monitored using tip-timing sensors. The results of this validation measurement campaign are presented in this paper. They show a close agreement between the design calculations and the measured frequencies, amplitudes, and strains.Additionally, a test turbine has been set-up featuring a direct scaling of the new LP backend with the new high strength steel and a pre-stage to simulate realistic operation conditions over the complete operation range. The blade performance was tested up to high mass-flows, condenser pressures of up to 300mbar and at varying load points covering all potential load points from extreme part load to full load with minimal and maximal condenser pressure. For the monitoring of the end-stage blade, dynamic strain gauges as well as tip-timing were employed. The results presented here show, that throughout the complete measurement campaign the blade experienced minimal excitation which led to amplitudes that allowed unrestricted operation in the completed tested operation range.In summary this paper shows the main design features of a large full-speed free-standing end-stage blade and the validation measures that were performed to ensure that the design targets and the market requirements are fully met.&nbsp;References[1] Teuber, H., Barnickel, J.: “Development of a new high-strength steel for low pressure steam turbine end-stage blades”,&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;ASME-Paper GT2018-76395, Proceedings of the ASME Turbo Expo 2018, Oslo (Norway), 2018&nbsp;

Design and Validation of a Large Steam Turbine End-Stage Blade to Meet Current and Future Market Demands

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

Turbo Expo 2021

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.