Mathematical Modeling and Study of the Influent Aerodynamic Loads on the Strength Characteristics of Turbine Blades

Abstract

The working blades of the turbomachine are constantly subjected to periodic loads in time, for example, due to the unsteady interaction of the flow of successive rows of stator and rotor blades. It is almost impossible to avoid resonance in turbine blades, since the frequency band of the power excitation and the natural frequencies of the blade disk are broadband ranges and overlap ranges. Analysis of forced oscillations of the blade crown is an important part of the design of gas turbine engines. To analyze fatigue and predict the service life of a turbomachine blade, a history of the stressed load on the blade is required. However, a blade designed for safe operation at certain constant rotor speeds can be subjected to destructive loads during start-up and stop. During such operations, the blade experiences short-term resonant stresses when passing a critical value, which may be in the speed range through which the rotor accelerates. Fatigue due to these transient effects can accumulate and lead to failure. In this regard, the development of mathematical models of aerodynamic loads and application for solving problems of ensuring the vibrational reliability of the blade apparatus is an urgent task. This paper presents a methodology for assessing aerodynamic loads and fatigue damage when operating at variable speed. The transient resonant stresses for the blade were determined using a numerical procedure. The procedure for assessing fatigue damage is described. The fatigue fracture surface is formed on the S-N-mean stress axes, and the Goodman rule is used to assess fatigue accumulation.