Forced Response Sensitivity of a Mistuned Rotor From an Embedded Compressor Stage

Abstract

The frequency mistuning that occurs due to manufacturing variations and wear and tear of the blades has been shown to significantly affect the flutter and forced response behavior of a blade row. While tuned computational fluid dynamics (CFD) analyses are now an integral part of the design process, designers need a fast method to evaluate the localized high blade responses due to mistuning. In this research, steady and unsteady analyses are conducted on the second-stage rotor of an axial compressor, excited at the first torsion vibratory mode. A deterministic mistuning analysis is conducted using the numerical modal forces and the individual blade frequencies obtained experimentally by tip timing data. The mistuned blade responses are compared in the physical and traveling wave coordinates to the experimental data. The individual and combined impacts of frequency, aerodynamic, and forcing function perturbations on the predictions are assessed, highlighting the need to study mistuned systems probabilistically.

Maximum mistuning amplification of the forced response vibration of turbomachinery rotors in the presence of aerodynamic damping

“…The distributions of aerodynamic frequency correction and damping used in this paper are given by a very simple toy model (constant value plus the first ND harmonic, see Fig. 3), which has been introduced with the idea of capturing just some of the basic characteristics of the data shown in Figure 4 of [16]: higher damping for negative TW index, lower for positive TW index, and a damping level below 0.0025.…”

“…The value of the maximum amplification factor from (16) and the large mistuning value from (17) are plotted as thick lines in Fig. 4.…”

“…The effect of mistuning on the forced response of a rotor with aerodynamic damping is more complicated, and changes substantially with respect to the uniform material damping case. There is even the possibility of having a reduction (by a factor of 2 or more) of the forced response vibration amplitude by the effect of mistuning, as it has been reported in [11,12] and found in many configurations [13,14,15,16]. The reason for this change in the effect of mistuning relies in the fact that the aerodynamic damping has different values for the different travelling wave (TW) modes of the tuned structure.…”

“…The analyses available in the literature of the forced response of a mistuned rotor with aerodynamic damping typically perform statistical explorations and optimizations on full FEM models and reduced order models [11,12,14,16]. The purpose of this paper is to analyze the effect of mistuning using the AMM methodology [17,7,8].…”

Analysis of mistuned forced response in an axial high-pressure compressor rig with focus on Tyler–Sofrin modes

“…Such a ROM is traditionally used to study the effect of mistuning on the forced vibration behaviour due to a single engine order excitation acting on a single travelling wave mode (TWM) (2,7,13,14) . The derived frequency response functions (FRFs) and blade individual vibration amplitudes can then be compared with those obtained in measurementssometimes with unsatisfying agreement on some of the blades and unexpected nodal diameter content in the response (13) . This might be due to the simplification of the force vector by restricting it to act on a single nodal diameter which does not hold in generalespecially in a multistage engine.…”