Detection of Blade Mistuning in a Low Pressure Turbine Rotor Resulting from Manufacturing Tolerances and Differences in Blade Mounting

Abstract

For a serious prediction of vibration characteristics of any structure, a detailed knowledge of the modal characteristic is essential. This is especially important for bladed turbine rotors. Mistuning of the blading of a turbine rotor can appear due to manufacturing tolerances or because of the blading process itself due to unequal mounting of the blades into the disk. This paper investigates the mistuning of the individual blades of a low pressure turbine with respect to the effects mentioned above. Two different rotors with different aerodynamic design of the blades were investigated. The blades were mounted to the disk with a so-called hammer head root which is especially prone to mounting irregularities. For detailed investigations, the rotor was excited with a shaker system to detect the forced response behavior of the individual blades. The measurements were done with a laser vibrometer system. As the excitation of rotor structure was held constant during measurement, it was possible to detect the line of nodes and mode shapes as well. It could be shown that the assembly process has an influence on the mistuning. The data were analyzed and compared with numerical results. For this, different contact models and boundary conditions were used. The above described characterization of modal behavior of the rotor is the basis for the upcoming aeroelastic investigations and especially for the blade vibration measurements of the rotor, turning with design and off-design speeds.

Fatigue life prediction of mistuned steam turbine blades subjected to deviations in blade geometry

“…Dynamic stresses are influenced by the magnitude and source of excitation, the damping of the blade, and the degree of geometrical mistuning of the turbomachinery blade [18]. Dimensional imperfections and deviations are due to tolerances and manufacturing process, material inhomogeneity, and wear in service [19]. These deviations lead to mistuning and can increase the forced response vibration amplitude, increasing the HCF; this is commonly called mistuning.…”

Fatigue life prediction of turbine blades with geometric imperfections made of stainless steel

“…The intrinsic ductile nature of ASTM 304 stainless steel facilitates a nuanced plastic deformation at the root contact, thereby enhancing the distribution of loads. This property holds significant implications for preventing failures and cracks, as underscored by findings reported in the study by Schönleitner et al [5]. Consequently, the selection of ASTM 304 stainless steel as the focal material for this investigation is rooted in its tailored characteristics to address the critical challenges associated with steam turbine blade performance.…”

“…Research conducted by Rao and Vyas [4] found that dynamic stresses are influenced by the magnitude and source of the excitation, blade damping and the degree of the turbomachinery blade geometrical mistuning. As highlighted by Schönleitner et al [5], dimensional imperfections and deviations are due to the tolerances and manufacturing process, material inhomogeneity and in-service wear. These deviations lead to structural mistuning and can increase the forced response vibration amplitude which increases HCF.…”

Prediction of fatigue life of geometrically deviated steam turbine blades under thermo-mechanical conditions

“…The 304 stainless steel is favored for its wide application, especially in blades subject to significant centrifugal and bending loads within steam turbines. Its remarkable ductility allows for nuanced plastic deformation at the root contact, preventing failures and cracks, as seen in Schönleitner et al (2015). This material is chosen for its tailored characteristics that address steam turbine blade challenges, and this paper thoroughly examines the behavior of the material in the context of steam turbine applications.…”