ANALYSIS OF IMPROVED AND ORIGINAL DESIGNS OF A 16 INCH LONG PENULTIMATE STAGE TURBINE BLADE

摘要

A finite element analysis of 16 inch long penultimate stage (L-1) blade was carried out to evaluate the improved and the original designs.The original design of the blade involved the "blade-tenon-shroud" system to make blade groups (6 blades per group). The improved design applied the concept of Integral Shroud Blade (ISB). Thus all the blades made a 360 degree group.The paper presents an application of the finite element analysis method to compute the natural frequencies, steady-state and alternating stresses, deformation due to forces acting on the blades and modal shapes of the blade group. In the case of the improved design it was also necessary to carry out computation of the dynamic response of a 360 degree blade-disk arc. This was to include the effect of the flexible disk fastening where blade and disk interaction were important to identify certain resonant conditions.It was concluded from the finite element results, that the steady-state stresses in the improved blade were lower, and the tangential mode shapes were eliminated. This was a great advantage since in the original design the first tangential mode shape and the higher steady-state stresses in the tenon contributed to the frequent failure of the "blade-tenon-shroud" system.