The computation of the unbalance vibration response of aero-engine assemblies fitted with nonlinear bearings requires the retention of a very large number of modes for reliable results. This renders most previously proposed nonlinear solvers unsuitable for this application. This paper presents three methods for the efficient solution of the problem. The first method is the recently developed impulsive receptance method (IRM). The second method is a reformulation of the Newmark-Beta method. In addition to these two time-domain methods, a whole-engine receptance harmonic balance method (RHBM) is introduced that allows, for the first time, the frequency domain calculation of the periodic vibration response of a real engine. All three methods use modal data calculated from a one-off analysis of the linear part of the engine at zero speed. Simulations on a realistically-sized representative twin-spool engine model with squeeze-film damper bearings provide evidence that the popular Newmark-Beta method can be unreliable for large order nonlinear systems. The excellent correlation between the IRM and RHBM results demonstrates the efficacy of these two complementary tools in the computational analysis of realistic whole-engine models.
Essential to effective aeroengine design is the rapid simulation of the dynamic performance of a variety of engine and non-linear squeeze-film damper (SFD) bearing configurations. Using recently introduced non-linear solvers combined with non-parametric identification of high-accuracy bearing models it is possible to run full-engine rotordynamic simulations, in both the time and frequency domains, at a fraction of the previous computational cost. Using a novel reduced form of Chebyshev polynomial fits, efficient and accurate identification of the numerical solution to the two-dimensional Reynolds equation (RE) is achieved. The engine analysed is a twinspool five-SFD engine model provided by a leading manufacturer. Whole-engine simulations obtained using Chebyshev-identified bearing models of the finite difference (FD) solution to the RE are compared with those obtained from the original FD bearing models. For both time and frequency domain analysis, the Chebyshev-identified bearing models are shown to mimic accurately and consistently the simulations obtained from the FD models in under 10 per cent of the computational time. An illustrative parameter study is performed to demonstrate the unparalleled capabilities of the combination of recently developed and novel techniques utilised in this paper.
The integration of squeeze-film dampers (SFDs) in aero-engine assemblies is a highly cost-effective means of introducing damping in an otherwise lightly damped structure. However, their deployment requires careful unbalance response calculations that take due account of the SFDs’ nonlinearity, particularly when they are unsupported by a centralising spring. Until recently, such calculations were prohibitive due to the large number of assembly modes that typically need to be considered. This problem has been overcome by the authors through the novel Impulsive Receptance Method (IRM) and the Receptance Harmonic Balance Method (RHBM), which efficiently solve the nonlinear problem in the time and frequency domains respectively. These methods have been illustrated on a realistic twin-spool engine and have been shown to be effective for both single frequency unbalance (SFU) excitation (unbalance on a single rotor) and multi-frequency unbalance (MFU) excitation (unbalance on both rotors). In the present paper, the methods are applied to a realistic three-spool engine and the aims are two fold: i) to present some preliminary results of a parametric study into a three-spool aero-engine assembly; ii) to propose a technique that makes use of both IRM and RHBM in producing the speed responses under MFU excitation (from all three rotors), with a realistic speed relation between the rotors. The latter technique is necessary since the speed ratio will vary along a realistic speed characteristic and the authors have previously solved the twin-spool MFU problem under a constant speed ratio condition. The approach used here is to approximate the speed characteristic by one in which the speed ratios are ratios of low integers, enabling the use of RHBM to finish off (to steady state) time-transient solutions obtained through IRM. The parameter study shows that the application of simple bump-spring supports to selected, otherwise unsupported, SFDs, along with slight sealing, should have a beneficial effect on the dynamic response of aero-engines with heavy rotors.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.