2 research outputs found
Generalised analysis of compensating balancing sleeves with experimental results from a scaled industrial turbine coupling shaft
The paper furthers the analysis of a recently proposed balancing methodology for high-speed,
flexible shafts. This mechanism imparts corrective balancing moments, having the effect of\ud
simulating the fixing moments of equivalent double or single encastre mounted shafts. This
is shown to theoretically eliminate/nullify the 1st lateral critical speed (LCS), and thereby
facilitate safe operation with reduced LCS margins. The paper extends previously reported
research to encompass a more generalised case of multiple, concentrated, residual
imbalances, thereby facilitating analysis of any imbalance distribution along the shaft.
Solutions provide greater insight of the behaviour of the balancing sleeve concept, and the
beneficial implications for engineering design. Specifically: 1) a series of concentrated
imbalances can be regarded as an equivalent level of uniform eccentricity, and balance sleeve
compensation is equally applicable to a generalised unbalanced distribution, 2) compensation
depends on the sum of the applied balancing sleeve moments and can therefore be achieved
using a single balancing sleeve (thereby simulating a single encastre shaft), 3) compensation
of the 2nd critical speed, and to a lesser extent higher orders, is possible by use of two
balancing sleeves, positioned at shaft ends, 4) the concept facilitates on-site commissioning
of trim balance which requires a means of adjustment at only one end of the shaft, 5) the
Reaction Ratio, RR, (simply supported/ encastre), is independent of residual eccentricity, so
that the implied benefits resulting from the ratio (possible reductions in the equivalent level
of eccentricity) are additional to any balancing procedures undertaken prior to encastre
simulation. Analysis shows that equivalent reductions in the order of 1/25th, are possible.
Experimental measurements from a scaled model of a typical drive coupling employed on an
industrial gas turbine package, loaded asymmetrically with a concentrated point of
imbalance, are used to support the analysis and conclusions
Theoretical investigation into balancing high-speed flexible shafts, by the use of a novel compensating balancing sleeve
Traditional techniques for balancing long, flexible, high-speed rotating shafts are inadequate over a full range of shaft speeds. This problem is compounded by limitations within the manufacturing process, which have resulted in increasing problems with lateral vibrations and hence increased the failure rates of bearings in practical applications. There is a need to develop a novel strategy for balancing these coupling shafts that is low cost, robust under typically long-term operating conditions and amenable to on-site remediation. This paper proposes a new method of balancing long, flexible couplings by means of a pair of balancing sleeve arms that are integrally attached to each end of the coupling shaft. Balance corrections are applied to the free ends of the arms in order to apply a corrective centrifugal force to the coupling shaft in order to limit shaft-end reaction forces and to impart a corrective bending moment to the drive shaft that limits shaft deflection. The aim of this paper is to demonstrate the potential of this method, via the mathematical analysis of a plain, simply supported tube with uniform eccentricity and to show that any drive shaft, even with irregular geometry and/or imbalance, can be converted to an equivalent encastre case. This allows for the theoretical possibility of eliminating the first simply supported critical speed, thereby reducing the need for very large lateral critical speed margins, as this requirement constrains design flexibility. Although the analysis is performed on a sub 15 MW gas turbine, it is anticipated that this mechanism would be beneficial on any shaft system with high-flexibility/shaft deflection.The work presented in this paper is supported by Siemens
Industrial Turbomachinery Limited, Lincoln, U