Experimental techniques and fixture design related to steam-turbine blade frequency measurements

The natural frequencies of “rugged” steam-turbine governing-stage impulse blades determined analytically must be verified experimentally when used singly, brazed in pairs or riveted in groups. The most desirable experimental data of natural frequencies and vibratory stresses would be the data which are obtained when the turbine blades are performing in their normal environment. In large steam-turbine units, these ideal experimental data are currently almost impossible to obtain due to inaccessibility even though resonant frequencies rotating turbomachines. Therefore, modified environments must be developed which will provide realistic experimental data for specif turbine-blade structures. Experimental techniques, fixture design, problems encountered in developing the techniques and fixtures, and versatility of the modified static environment are reported in this paper.