ANALYSIS OFVIBRATORY STRESS OF INTEGRAL SHROUD BLADE FOR MECHANICAL DRIVE STEAMTURBINE by Yasutomo Kaneko
The advanced integral shroud blade (ISB) structure has been developed to improve the reliability and thermal efficiency of mechanical drive steam turbines. This advanced ISB has been applied to not only the control stage blades but also the intermediate stage blades. Turbines using these advanced blades have been successfully operated. This paper presents the analysis method to calculate the vibratory stresses of the ISB caused by the stage interaction force and the shock load. The vibration response characteristics are explained and comparisons are made to the advanced ISB structure and the conventional grouped blade structure, using the calculated results. Additional verification test results to confirm the validity of the proposed analysis method are also shown.
An Analysis System for Blade Forced Response
A frequent cause of turbomachinery blade failure is excessive resonant response. The most common excitation source is the nonuniform flow field generated by inlet distortion, wakes, and/or pressure disturbances from adjacent blade rows. The standard method for dealing with this problem is to avoid resonant conditions using a Campbell diagram. Unfortunately, it is impossible to avoid all resonant conditions. Therefore, judgements based on past experience are used to determine the acceptability of a blade design.A new analysis system has been developed to predict blade forced response. The system provides a design tool, over and above the standard Campbell diagram approach, for predicting potential forced response problems. The incoming excitation sources are modeled using a semi-empirical rotor wake/vortex model for wake excitation, measured data for inlet distortion, and a quasi-3D Euler code for pressure disturbances. Using these aerodynamic stimuli, and the blade’s natural frequencies and mode shapes from a finite element model, the unsteady aerodynamic modal forces and the aerodynamic damping are calculated. A modal response solution is then performed.This system has been applied to current engine designs. A recent investigation involved fan blade response due to inlet distortion. An aeromechanical test had been run with two different distortion screens. The resulting distortion entering the fan was measured. With this as input data, the predicted response agreed almost exactly with the measured response. In another application, the response of the LPT blades of a counter-rotating supersonic turbine was determined. In this case the blades were excited by both a wake and a shock wave. The shock response was predicted to be three times larger than that of the wake. Thus, the system identified a new forcing function mechanism for supersonic turbines.This paper provides a basic description of the system, which includes: 1) models for the wake excitation, inlet distortion, and pressure disturbance; 2) a kernel function solution technique for unsteady aerodynamics; and 3) a modal aeroelastic solution using strip theory. Also, results of the two applications are presented.© 1992 ASME
On the Prediction of Unsteady Forces on Gas-Turbine Blades: Part 2 — Viscous-Wake-Interaction and Axial-Gap Effects
This paper is a contribution to the study of the generation of unsteady forces on turbine blades due to viscous wake interaction and potential-flow interaction from upstream blade rows. A computer program is used to compute the unsteady forces on a rotor. Typical results for isolated viscous-wake interaction (no potential-flow interaction) are shown. These results indicate that the first spatial harmonic of the unsteady force may decrease for higher stator-to-rotor-pitch ratios. This trend is explained by considering the mechanisms by which the unsteady forces are generated. The mechanism by which the viscous wakes affect the flow field to generate these unsteady forces is shown to vary with the stator-to-rotor-pitch ratio and with the outlet flow angle of the stator. It is also shown that by varying the axial gap between rotor and stator one can attempt to minimize the magnitude of the unsteady part of the forces generated by the combined effects of viscous-wake interaction and potential-flow interaction.Copyright © 1988 by ASME