Analysis of Geometric Errors of Throat Sizes of Last Stage Blades in a Mid-Size Steam Turbine

Abstract

Steam turbine technology with enhanced flexibility will continue to participate in electric power supply mixes. Last stage blades secure the reliability of a steam turbine and require high precision manufacturing and assembly. This case study presents a statistical analysis of geometric errors of the throat sizes of the last stage blades in a mid-size steam turbine. A 3D optical scanner is employed to capture detailed geometries of rotor blades and a half of assembled nozzle diaphragm. Unrolled cylinder cross-sections are used to evaluate 2D geometrical features such as blade throats and areas at three different diameters, and the results are compared to intended designs. In addition, linear correlations between the throat size and blade pitch, area and trailing edge thickness are established, and blade throat position shifts are quantified. Such a comprehensive study is presented for the first time, and some useful conclusions can be retrieved from this case study.

Flutter Measurement of a Linear Turbine Blade Cascade with an Angular Position Deviation of One Blade

“…This initial research effort opened the door to a more extensive testing campaign. The intended types of position deviations will be realized according to the actual geometric errors, emphasizing the effect on the blade throat size and position [1][2][3]. In such investigations, a non-dimensional or otherwise generalizable form of the deviations and their effects will be preferred to provide information on the relative importance.…”

“…The quality of production and assembly of bladed discs is essential for the performance and safe operation of turbomachinery. However, geometric errors are unavoidable [1][2][3][4] and manufacturing and assembly imperfections may play a role in dynamic unbalance, mistuning or vibration of the bladed discs. There are two main mechanisms of blade row vibration: forced response due to blade row interaction phenomena or inflow distortion and self-excited oscillation known as flutter.…”