Rotor-Stator Interactions in a 2.5-Stage Axial Compressor-Part I: Experimental Analysis of Tyler-Sofrin Modes

This two-part paper investigates the influence of rotor-stator interactions on the blade vibrational stresses of the first rotor, excited by the downstream stator. To this end, aeroacoustic and aeroelastic measurements and numerical setup studies for the solver TRACE are conducted in order to improve the predictive accuracy of blade vibrational stresses. Part I compares tip timing data for resonance crossings of three blisk modes to numerical predictions. Due to the single-row analysis within the linearized version of the flow solver TRACE, unsteady rotor-stator interactions are excluded by default. The findings show that leaving out these interactions in the numerical setup can lead to 97% lower vibrational stress predictions with respect to the absolute value measured. To validate the prediction of rotor-stator interactions by the nonlinear frequency domain method of TRACE, unsteady pressure measurements were conducted at the casing in the inter-row section of the first stage. The results were analyzed using an optimized measuring grid and applying a compressed sensing-based azimuthal mode analysis. Predicted azimuthal mode numbers are in accordance with the experiment, whereas amplitudes deviate from the measurements in part. Part II focuses on the prediction of blade vibrational stresses. To this end, a detailed grid study is performed and comparisons to steady and unsteady measurement data are made. In summary, this two-part paper confirms the importance of rotor-stator interactions for blade vibrational stresses excited by downstream vanes at a state-of-the-art high-pressure compressor.