The prediction of the non-linear dynamics of a squeeze-film damped aero-engine rotor housed in a flexible support structure

Abstract

This paper shows how the non-linear dynamics of a rotor running in unsupported squeeze-film dampers (SFDs) housed in a flexible support structure can be efficiently modelled using an integrated analytical technique and a standard model for the SFDs. A test rig that reproduces, to a limited extent, the essential dynamic features of an aero-engine gas turbine is considered and the aim of the analysis is to assess the ability to predict and interpret the observed non-linear vibrations as indicated by amplitude-speed plots, frequency spectra, orbital motion plots and Poincare´maps. The solution process starts with the application of a fast harmonic balance method that uses receptance functions to determine periodic solutions. A modal-based approach is then used for the analysis of the stability and bifurcation of these solutions, as well as the analysis of aperiodic motion. The simulation correctly predicts the overall performance, including subharmonic motion, combination frequencies and subcritical superharmonic resonances.

Prediction method for steady-state response of local rubbing blade-rotor systems

“…For example, Bonellop [13] developed the receptance HB method to rapidly compute the steady-state periodic vibration of an entire aeroengine model. Similar methods were proposed by other researchers [14][15][16]. Wei and Zheng [8] conducted multi-harmonic response analysis of a dynamic system with local nonlinearities based on the DF method and linear receptance data.…”

“…(15) and (17) is that the coefficients in Eq. (15) are complex numbers, and thus, the IHB method cannot be used directly.…”

Empirical identification of the inverse model of a squeeze-film damper bearing using neural networks and its application to a nonlinear inverse problem

“…However, it is also well known that, under certain conditions, particulary high static loading, an SFD system can exhibit sub-harmonics in its response e.g. (Bonello et al., 2004b). Indeed, in the general case of RHBM, the fundamental frequency of the vibration would be a sub-harmonic Ω/Q where Q is a positive integer (Bonello and Pham, 2009).…”

A theoretical and experimental investigation of the dynamic response of a squeeze-film damped twin-shaft test rig

“…This phenomenon marks a 'bifurcation' in the system dynamics, with the resultant stable vibration being either subharmonic, or more generally, aperiodic and termed '2-frequency' vibration as its frequency spectrum is composed of linear combinations k 1 f 1 AE k 0 f 0 of two fundamental frequencies f 1 , f 0 (k 0 is an integer). 5,6 In the case of MFU excitation of a linear system (as in the linear model of the dual-rotor system 7 ) the vibration response is simply the superposition of the responses to the individual rotors' unbalance excitations. However, in the case of MFU excitation of a nonlinear system (as in the real aero-engine) the vibrations induced by the individual unbalances are effectively 'mixed', so that the resultant frequency spectrum of the nominal vibration response of a twin-spool engine, for example, will have 'combination frequencies' of the general form k 1 f 1 AE k 2 f 2 where k 1 , k 2 are integers and f 1 , f 2 are the rotor speeds.…”

“…Hence, the line of enquiry in Holmes and Dede's work 8 was not followed up, with research continuing on the nonlinear dynamics of single-rotor SFD systems. 5,6,[10][11][12] Moreover, unlike the test rig of Holmes and Dede, 8 recent experimental studies on SFDs in the multi-shaft context [13][14][15] are not particularly relevant to the representative engine types in Figure 1. For example, all test rigs in previous studies [13][14][15] involve a supported SFD (whose degree of nonlinearity is considerably less than an unsupported SFD); in Delgado and Andres' experiment, 13 the shaft is oriented vertically and in the dual-shaft test rigs of Gilbert et al 14 and Gupta and Chatterjee, 15 the SFD is supported by a parallel retainer (centralising) spring (squirrel cage).…”