ASSESSING FAN AND COMPRESSOR BLADE HCF SENSITIVITY TO NON-UNIFORM INLET FLOWS

摘要

In recent years, the subject of high cycle forced response excitation of aircraft turbine engine components and resulting fatigue failures (HCF) has been of increasing concern. Prediction and test methods are needed that can identify inlet distortion-related HCF drivers and response, and support assessment and correction of potential problems before failure occurs. The present paper describes a method by which inlet distortions may be examined for flow-distortion-driven HCF excitation potential in a test situation. The method was derived from results of a distortion screen test that produced periodic excitation in a two-stage transonic fan. A CFD method is used to predict the unsteady pressure field on the first stage blades due to a harmonic component of the measured total pressure distortion. A finite element (FE) model of the blade is then used to identify modal frequencies and predict vibratory stress and strain, providing information on the HCF potential and sensitivity to the imposed distortion. The method avoids the need for a full unsteady, coupled CFD-FE model of the entire compressor flowpath, and the calculations can be conducted rapidly. For the case evaluated, it is shown to produce stress predictions that compare to within 5% of the experimental values.