Reduced Order Modeling of Forced Response in a Multistage Compressor Under Mistuning and Aerocoupling

Abstract

Vibration amplitudes and fatigue life in multistage turbomachinery are commonly estimated by an investigation of the individual stages. Research is currently extending the scope to include strucural and aeroelastic inter-stage coupling. Both effects have been shown to significantly influence blade vibrations. For safe operation of modern blisk blading with its lower structural damping due to the elimination of frictional contacts at the blade roots, an accurate prediction of the vibration behavior with mistuning is necessary to avoid high cycle fatigue failures. In this paper, a cyclic Craig-Bampton reduction method with a-priori interface reduction for multistage rotors is extended to handle aeroelastic effects. This reduced order model efficiently predicts forced response in multistage applications. Aeroelastic multistage simulations are carried out using the harmonic balance method to account for the stage interactions and yield damping and stiffness coefficients, as well as excitation forces. Small structural mistuning is projected onto the tuned system modes of the rotor. The approach is applied to a two-stage compressor configuration. Monte Carlo simulations show the sensitivity of vibration amplitudes to the aeroelastic coupling for mistuning. The aeroelastic inter-stage coupling is found to originate mainly from acoustic mode propagation between the stages. The fatigue of rotor blades is significantly affected by multistage interactions since vibration amplitudes increase due to the superposition of the responses of multiple modes. This leads to the conclusion that aeroelastic multistage effects need to be incorporated in future design procedures to allow for an accurate prediction of fatigue life.

An improved reduced order model for bladed disks including multistage aeroelastic and structural coupling

“…The aeroelastic coefficients are calculated using the finished structural ROM, using the method described in Maroldt et al (2022b) and discussed below in the section Aeroelastic Analysis. For each DOF of the ROM a flutter simulation is performed.…”

“…The FEM model uses mostly quadratic hexahedral elements and has a total number of 1.96 million DOFs. For more details see Maroldt et al (2022b).…”

“…Aeroelastic simulations were only conducted for the 2 1=2-stage axial compressor, as it features realistic blade geometries. A detailed description of the CFD approach is described by Maroldt et al (2022b), however, a brief summary is given below.…”

“…Only little work on ROMs for multi-stage turbomachinery, including aeroelastic coupling, has been reported in the open literature. Maroldt et al (2022b) extended the model of Schwerdt et al (2019) to include inter-stage aeroelastic coupling, showing that multi-stage excitation and inter-stage coupling can have a significant influence on vibration amplitudes and mistuning. The aeroelastic calculations were performed using a CFD nonlinear harmonic balance approach, which allows for multi-row coupling.…”

“…This reduction method was extended by Schwerdt et al (2019) to include polynomial basis functions for the interface in addition to the Fourier basis, thereby reducing the number of necessary interface DOFs and eliminating the need for the nodes to have the same number of rings for both adjacent stages. The original and extended methods were applied to different problems, some of them including friction and aeroelastic effects (D'Souza et al, 2012;Battiato et al, 2018;Maroldt et al, 2022b).…”