During the commissioning of a low pressure steam turbine the last stage blades experienced severe vibration levels. An inspection revealed cracks in the blades and failures of lashing wires. Cracked blades were substituted and a tip timing measurement system was installed for monitoring last stage blade vibrations, in order to investigate the dynamic behaviour of the blade row in different operating conditions. The main results of this test campaign are presented in the paper: the severe vibrations were due to a fluid-dynamic instability coupled to one vibration mode of the blade group (also called flutter instability). A modified blade has also been designed in order to reduce its sensitivity to the operating conditions which could cause the instability. Its dynamic behaviour has been numerically investigated, the grouping of blades in packs has been optimized in order to avoid resonances with engine order excitations, and finally the new blades have been substituted in the turbine. The measurement results which are briefly described in the paper have shown a considerable improvement of the turbine dynamic behaviour.

Analysis of LP steam turbine blade vibrations: experimental results and numerical simulations

BACHSCHMID, NICOLO';CHATTERTON, STEVEN
2012

Abstract

During the commissioning of a low pressure steam turbine the last stage blades experienced severe vibration levels. An inspection revealed cracks in the blades and failures of lashing wires. Cracked blades were substituted and a tip timing measurement system was installed for monitoring last stage blade vibrations, in order to investigate the dynamic behaviour of the blade row in different operating conditions. The main results of this test campaign are presented in the paper: the severe vibrations were due to a fluid-dynamic instability coupled to one vibration mode of the blade group (also called flutter instability). A modified blade has also been designed in order to reduce its sensitivity to the operating conditions which could cause the instability. Its dynamic behaviour has been numerically investigated, the grouping of blades in packs has been optimized in order to avoid resonances with engine order excitations, and finally the new blades have been substituted in the turbine. The measurement results which are briefly described in the paper have shown a considerable improvement of the turbine dynamic behaviour.
Institution of Mechanical Engineers - 10th International Conference on Vibrations in Rotating Machinery
9780857094520
steam turbine; blade vibrations; tip timing
File in questo prodotto:
File Dimensione Formato  
VIRM10 - Analysis of LP steam turbine blade vibrations experimental results.pdf

Accesso riservato

: Post-Print (DRAFT o Author’s Accepted Manuscript-AAM)
Dimensione 1.13 MB
Formato Adobe PDF
1.13 MB Adobe PDF   Visualizza/Apri

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11311/678357
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 9
  • ???jsp.display-item.citation.isi??? ND
social impact