A Photoelastic Study of a Fir-Tree Steam Turbin Dovetail

Abstract

In turbine design, because the joint between the turbine blade and the rotor bears the largest stress, it is important to study the stress at this position. The fir-tree type is one of the most efficient joint configurations for blade fastenings. Many papers have reported on the fir-tree turbine blade, but these mostly dealt with experiments using two-dimensional analysis. We therefore experimented with three-dimensional stress analysis in frozen photoelasticity. In this examination, the study was made of characteristic occurrences under centrifugal force produced by rotation simulating an actual turbine. The analysis of the fir-tree joint was performed for two tests. One was for straight entry and the other was for curved entry. Photographs were obtained for the photoelastic fringe, stress distribution, and stress concentration factors. The results were as follows radially, in both the straight and curved entry types, the highest stress concentration occurred at the tip serration. Axially, in the curved entry type, the highest stress concentration point was the axial center, and in the straight entry type, the distribution was uniform. © 1993, The Japan Society of Mechanical Engineers. All rights reserved.