Actual trend in steam turbine design is to use blades with integral shrouds, for high pressure and intermediate pressure steam turbine sections, as well as sometimes also for the long blades of the low pressure sections.The blades are either inserted with their root into the seat on the shaft in such a way that small clearances remain between adjacent blade shrouds, so that the relative vibration amplitude is restricted by the contact between adjacent shrouds. This mechanism is called “snubbing mechanism”. Another technology for mounting blades on the shaft is to do it in such a way that the blades are slightly forced against each other in correspondence of the shrouds: this should allow the continuity of the contact without clearances also at rated speed and full load. In this case the blades are called “pre-twisted”. Field experience has shown that these kinds of blade rows has a “robust and smooth” behavior. But there is still some lack of theoretical/numerical investigation for defining its dynamical behavior in different operating conditions, both for the blades with clearance and with pre-twist. The aim of this paper is to investigate numerically the non-linear dynamic behavior of a couple of shrouded blades, taking account of contact forces and friction. An equivalent linear model has then been developed for analyzing the behavior of the complete blade row. Also some provisional experimental results on non-rotating blade rows are presented.

Some results in analyzing the dynamic behavior of blade rows coupled by shroud contacts

BACHSCHMID, NICOLO';PENNACCHI, PAOLO EMILIO LINO MARIA;
2011-01-01

Abstract

Actual trend in steam turbine design is to use blades with integral shrouds, for high pressure and intermediate pressure steam turbine sections, as well as sometimes also for the long blades of the low pressure sections.The blades are either inserted with their root into the seat on the shaft in such a way that small clearances remain between adjacent blade shrouds, so that the relative vibration amplitude is restricted by the contact between adjacent shrouds. This mechanism is called “snubbing mechanism”. Another technology for mounting blades on the shaft is to do it in such a way that the blades are slightly forced against each other in correspondence of the shrouds: this should allow the continuity of the contact without clearances also at rated speed and full load. In this case the blades are called “pre-twisted”. Field experience has shown that these kinds of blade rows has a “robust and smooth” behavior. But there is still some lack of theoretical/numerical investigation for defining its dynamical behavior in different operating conditions, both for the blades with clearance and with pre-twist. The aim of this paper is to investigate numerically the non-linear dynamic behavior of a couple of shrouded blades, taking account of contact forces and friction. An equivalent linear model has then been developed for analyzing the behavior of the complete blade row. Also some provisional experimental results on non-rotating blade rows are presented.
2011
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11311/576522
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