Peculiarities of the vibrations of shrouded blades in power turbines

Conclusions

• 1. The necessity to account for restraining the torsion of the blade section for vibrations of shrouded blades irrespective of how long they are made has been shown. The experimental and calculated data presented testify to the fact that the law of distribution of the normal stresses in the peripheral section of a shrouded blade vibrating mainly torsionally coincides with the law of variation of the torsion function along the periphery of the blade section.

• 2. The experimental and calculated data confirm that, in the computations of the natural frequencies and modes of vibrations, it is necessary to consider that there is a complete absence of warping of the peripheral section of the blade. The condition of equality to zero of the bimoment at the peripheral section holds good for the vibrations of unshrouded blades. In the case of shrouded blades, this condition leads to a significant error in the determination of the stressed state.

• 3. It is shown that relatively high, mainly bending, stresses occur in the peripheral section of rotating shrouded blades particularly with interunit vibrations of the rim. In view of this, it is very advisable to take steps in the design stage itself to reduce the stress levels in the peripheral section of a shrouded blade.