Mistuned Higher-Order Mode Forced Response of an Embedded Compressor Rotor—Part II: Mistuned Forced Response Prediction

Abstract

This paper is the second part of a two-part paper that presents a comprehensive study of the higher-order mode (HOM) mistuned forced response of an embedded rotor blisk in a multistage axial research compressor. The resonant response of the second-stage rotor (R2) in its first chordwise bending (1CWB) mode due to the second harmonic of the periodic passing of its neighboring stators (S1 and S2) is investigated computationally and experimentally at three steady loading conditions in the Purdue three-stage compressor research facility. A nonintrusive stress measurement system (NSMS, or blade tip-timing) is used to measure the blade vibration. Two reduced-order mistuning models of different levels of fidelity are used, namely, the fundamental mistuning model (FMM) and the component mode mistuning (CMM), to predict the response. Although several modes in the 1CWB modal family appear in frequency veering and high modal density regions, they do not heavily participate in the response such that very similar results are produced by the FMM and the CMM models of different sizes. A significant response amplification factor of 1.5–2.0 is both measured and predicted, which is on the same order of magnitude of what was commonly reported for low-frequency modes. In this study, a good agreement between predictions and measurements is achieved for the deterministic analysis. This is complemented by a sensitivity analysis which shows that the mistuned system is highly sensitive to the discrepancies in the experimentally determined blade frequency mistuning.

Accounting for Circumferential Flow Nonuniformity in a Multistage Axial Compressor

“…In addition to one-dimensional performance metrics, the prediction of aerodynamic blade forcing functions in forced response vibratory conditions is an especially important topic in turbomachinery design as it drives rotor resonant vibratory response. However, in contrast to the enhanced capability achieved for mistuned forced response prediction [6,7], the influence of circumferential flow nonuniformity on aerodynamic excitation is less understood. The wake from the upstream blade row and the potential field from the downstream blade row are considered the main causes for excitation, and the aerodynamic excitation reduced from steady single-passage computational fluid dynamics (CFD) simulations [6,8] is typically used to predict the rotor resonant response.…”

Generalized SAFE Diagram for Mistuned Bladed Disks

“…Thus mistuning models need to be adapted to the measured modes, or in other words, following a phenomenological approach. This is particularly true for high-modes which are usually quite complex, most likely found in high modal density regions, and are even more sensitive to the mistuning itself [25,26]. The actual shapes and frequencies of the modes can be accurately obtained through Experimental Modal Analysis (EMA), and a comparison with the Finite Element (FE) nominal modes provides a direct assessment of the mistuning.…”