Concluding Remarks

LPT blades are sometimes welded in pairs to increase their flitter charac­teristics. It has been shown by means of two-dimensional simulations that the aerodynamic damping welded-pairs is larger than the one of single blades. This specially true for torsion modes and bending modes whose flapping direction is aligned with the tangential direction of the cascade. A more in depth dis-

cussion of the theoretical benefits of using such configurations requires taking into account the frequency and three-dimensional mode shape modification.

The frequency characteristics of three bladed-disk configurations have been presented. The three assemblies differ just in the boundary conditions of the tip-shroud. It has been observed that the frequency characteristics of the welded – pair configuration are essentially the same that the cantilever configuration while the interlock changes dramatically the overall behaviour of the assem­bly. The prediction of the stability or not of the welded-pair configuration requires to account for three-dimensional and mistuning effects. The stability of the interlock is compromised by the transition between edgewise and tor­sion modes with the nodal diameter of the first family. It is believed that the torsion modes with low reduced frequency, that the 2D simulations show are unstable, are responsible of the instability, this is consistent with the results of other researchers.

Acknowledgments

The authors wish to thank ITP for the permission to publish this paper and for its support during the project. This work has been partially funded by the Spanish Minister of Science and Technology under the PROFIT grant FIT – 100300-2002-4 to the School of Aeronautics of the UPM.

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