This paper is the first of a two-part publication that aims to experimentally evaluate, simulate and compare the aerodynamic and mechanical damping for a last stage steam turbine rotor blade at part load operation. Resulting strong off-design partial load regimes expose the last stage moving blade (LSMB) to the possible onset of aero-elastic instabilities, such as stalled and un-stalled flutter. This interaction can lead to asynchronous blade vibrations and then the risk of blade failures for high cycle fatigue. In this framework, it is necessary to develop and validate new tools for extending operating ranges, controlling non-synchronous phenomenon and supporting the design of new flutter resistant LSMB. To this end, a 3-stage downscaled steam turbine with a snubbered LSMB was designed by Ansaldo Energia and tested in the T10MW test facility of Doosan Skoda Power R&D Department within the FlexTurbine European project. The turbine was operated in a wet steam environment at very low volume flow conditions simulating different part load regimes. The steady flow field throughout the LSMB was characterized and the occurrence of flutter was investigated by inducing the blade resonance through an AC magnet excitation and measuring the overall damping. The results presented in this paper indicate that the blade always operates over the flutter stability margin validating this new blade design. In the second part of this work, the mechanical and aerodynamic contribution to the damping will be separated in order to validate the aerodynamic damping prediction of an upgraded CFD tool, already adopted in the design phase of the blade at design point.
S. P a t r o n e , R.PenC0, N. V a l l e ANSALDO COMPONENT1 V i a h.Lorenzi 8 Genova, 1-16152, I t a l y * INFN V i a Dodecaneso 33 ,Geneva, 1-16146 A&stract-Ansal&onpcoenti, underacontract ENEA, has developed t h e interlaver electrical-j o i n t s and c o i l terminations f o r a 12 T e s l a solenoid, 0.6m bore, Nb3Sn, "wind and react" t h a t w i l l be wound with a CIC conductor 13.8x13.8 mn2 i n dimensions. Both i n t e r l a y e r j o i n t s and terminations, i n c o i l operation condition, w i l l be subjected t o a magnetic f i e l d of about 8-10 T with a 6wL current. T e s t s on s h o r t e r l e n g t h i n t e r l a y e r j o i n t s and terminations, a t d i f f e r e n t magnetic f i e l d s and currents,were carried o u t a t MA.RI.SA test f a c i l i t y . The r e s i s t a n c e of a 140 mm long i n t e r l a y e r j o i n t a t B=8T and I=6wL was R=2.4x10-9 Ohm. The measured r e s i s t a n c e f o r a j o i n t b e t w e e n t w o t e r m i n a t i o n s ( 1 2 0 " l o n g ) , i n t h e samecondition, wasR=1.5x10-8Ohm.
Turbine blades are critical components in thermal power plants and their design process usually includes experimental tests in order to tune or confirm numerical analyses. These tests are generally carried out on full-scale rotors having some blades instrumented with strain gauges and usually involve a run-up and/or a run-down phase. The quantification of damping in these conditions is rather complicated, since the finite sweep velocity produces a distortion of the vibration amplitude in contrast to the Frequency-Response Function that would be expected for an infinitely slow crossing of the resonance. In this work, we show through a numerical simulation that the usual identification procedures lead to a systematic overestimation of damping due both to the finite sweep velocity, as well as to the variation of the blade natural frequency with the rotation speed. An identification procedure based on the time-frequency analysis is proposed and validated through numerical simulations.
The spin test is a standard industrial practice employed for the qualification of rotor blades and disks. The expected results are the modal properties of blades and assemblages at different rotation velocities. If a significant dynamic coupling among the blades exists, global vibration modes appear, reflecting into a set of closely spaced natural frequencies for each mode family. In case of perfectly-tuned bladed disks, the circumferential structure of the mode shapes is known and can be exploited during the identification process so that traditional single-dof models may be applied. On the contrary, the mode irregularities produced by mistuning prevents the use of single-dof models requiring the development of more sophisticated approaches. In this work, we propose a multi-dof identification technique organized as follow: 1) the FRF of the bladed disk in the neighborhood of a resonance crossing is identified by the wavelet transform of the measured response; 2) the modal parameters of the system are estimated using a mixed stochastic-deterministic subspace algorithm formulated in the frequency domain. The procedure is validated using a realistic numerical simulation.
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