High cycle fatigue (HCF) due to unforeseen excitation frequencies, underestimated force magnitudes, or a combination of both causes control-stage failures for steam turbine stakeholders. This paper provides an extended design criteria toolbox, as well as validation data, for control-stage design based on experimental data to reduce HCF incidents in partial-admission turbines. The upstream rotor in a two-stage air test turbine is instrumented with pressure transducers and strain gauges. Admission degrees extend from 28.6% to 100%, as one or two admission arcs are simulated by blocking segmental arcs immediately upstream of the first stator vanes with aerodynamically shaped filling blocks. Sweeps across a speed range of 50%–105% of design speed are performed at a constant turbine pressure ratio during simultaneous high-speed acquisition. A forced-response analysis is performed and results presented in Campbell diagrams. Partial admission creates a large number of low-engine-order forced responses because of the blockage, pumping, loading, and unloading processes. Combinations of the number of rotor blades and low-engine-order excitations are the principal sources of forced-response vibrations for the turbine studied here. Altering the stator and/or rotor pitches changes the excitation pattern. We observed that a relationship between the circumferential lengths of the admitted and nonadmitted arcs dictates the excitation forces and may serve as a design parameter.
Forced Response in Axial Turbines Under the Influence of Partial Admission
Contributed by International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 11, 2012; final manuscript received August 14, 2012; published online June 5, 2013. Assoc. Editor: David Wisler.
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Fridh, J., Laumert, B., and Fransson, T. (June 5, 2013). "Forced Response in Axial Turbines Under the Influence of Partial Admission." ASME. J. Turbomach. July 2013; 135(4): 041014. https://doi.org/10.1115/1.4007599
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