Full 3D rotor/stator interaction simulations in aircraft engines with time dependent angular speed

This contribution focuses on the simulation of rotor/stator interactions between an aircraft engine compressor blade and a rigid casing with a time dependent angular speed and accounting for centrifugal effects

Anti-optimisation applied to the analysis of rotor/stator interaction

There is a drive towards minimising operating clearances within turbomachines in order to limit reverse leakage flows and hence improve their efficiency. This increases the likelihood of contact occurring between the blade and the casing, which can give rise to high amplitude vibration. Modelling this in- teraction represents a significant computational challenge. The non-linear contact precludes the use of well-established linear methods, and is also subject to uncertainties: the contact law is imprecisely known and the exact geometry of imperfections that trigger contactmay be unknown. In this paper a novel approach is presented that aims to account for the uncertainties associated with the non-linearity in a non-probabilistic way. The worst case is sought, by fram- ing the systemas a constrained anti-optimisation problem. The target to be maximised represents a metric of the output of in- terest. The degrees of freedom of the anti-optimisation are the non-linear input forces (considered as external loads), and the constraints are designed to capturewhat is thought to be known about the non-linear contact law and geometry. A realistic three-dimensional model of a turbine blade is used to explore the approach, with contact considered at the leading and trailing edge. The blade dynamics are described in terms of a linear transfer function matrix and the target metric of interest is chosen to be the peak displacement of the contact Address all correspondence to this author: [email protected] points. The non-linearity is taken to result from an offset shaft, giving a sinusoidal clearance variation. The blade is driven at constant frequency and the scope of the study is limited to find- ing bounds on periodic solutions. A variety of constraint condi- tions are explored that describe aspects of the non-linearity. For example, only compressive forces are permitted (no tension from the contact), and the displacement must not exceed the clear- ance. The method yields encouraging initial results: constraints can be identified that give efficient estimates of the upper bound response of the system as a function of drive frequency. The re- sults are compared with a benchmark time-domain simulation and are found to correctly over-predict the response without be- ing overly conservative. Broad trends are also in agreementwith the benchmark solution. The proposed method appears to be a promising approach for efficiently accounting for uncertainties associated with the non-linearity and thus improving blade de- sign. Copyright © 2013 by ASME

Experimental and numerical simulation of a contact induced rotor/stator interaction inside an aircraft engine high-pressure compressor

The development of a predictive numerical strategy for the simulation of rotor/stator interactions is a concern for several aircraft engine manufacturers. As a matter of fact, modern designs of aircraft engines feature reduced operating clearances between rotating and static components which yields more frequent structural contacts. Subsequent interaction phenomena (be it rubbing events, modal interaction or whirl motions) are not yet fully understood. For that reason, experimental data obtained from set-ups dedicated to the simulation of such interactions are scrutinized and are key in: (1) increasing the knowledge of the interaction phenomena and (2) allowing for a calibration of the numerical models with realistic events. In this contribution, the focus is made on an experimental set-up in Snecma facilities. It features a full-scale high-pressure compressor stage and aims at simulating contact induced interactions between one of the blades (slightly longer than the other ones) and the surrounding abradable coating that is deposited along the casing circumference. For this experimental set-up, it is found that the witnessed interaction involves a single blade — thus it should be analyzed as a sequence of rubbing events — and more specifically its first torsional mode, which is its second free-vibration mode. The focus is made both on the presentation of the experimental set-up and on the confrontation with the numerical results. Numerical results are analyzed by means of adaptative signal processing techniques and the consistency between numerical results and experimental observations is underlined both in time and frequency domains. In particular, the numerical strategy developed for Snecma is shown to predict very accurately the nature of the interaction as wear patterns obtained experimentally and numerically are a match. This numerical/experimental confrontation is the first attempt to calibrate a sophisticated numerical strategy with experimental data acquired within the high-pressure compressor of an aircraft engine for the simulation of rotor/stator interactions. Contrary to previous studies carried out within the low-pressure compressor of an aircraft engine, this interaction is found to be non-divergent: high amplitudes of vibration are experimentally observed and numerically predicted over a very short period of time. The ability of the numerical strategy to predict torsion induced interactions opens avenues for further analyses in turbine stages and with more sophisticated models including mistuned bladed disks and multi-stage components.</jats:p

Numerical study of bladed structures with geometric and contact nonlinearities

peer reviewedThis paper deals with the reduced order modeling of turbomachine bladed structures accounting for both geometric nonlinearities and nonlinear blade-tips/casing contacts in a numerically efficient way. A recently derived methodology, based on the concept of modal derivatives, is first used to study the contact interactions of a single rotating blade impacting a rigid casing. In this reduction procedure, nonlinear internal forces due to large displacements are evaluated using the stiffness evaluation procedure and contact is numerically handled with Lagrange multipliers. In-depth analyses, including clearance consumption computations and frequency analyses with a continuation procedure, are performed to understand and characterize the combined influence of contact and geometric nonlinearities on the blade's dynamics. The methodology is then generalized to full bladed disks using Component Mode Synthesis techniques with fixed interfaces. Each sector of the cyclically symmetric structure is projected onto a reduction basis composed of Craig–Bampton modes and a selection of their modal derivatives. A second reduction allows reducing the cyclic boundary degrees-of-freedom. The methodology is first assessed using a harmonic excitation at blade-tips, without contact. When applied to the bladed disk subjected to contact interactions, the methodology allows identifying the main interaction speeds that can be detrimental for the engine integrity. Through this work, the numerical strategy is applied on an open industrial compressor bladed disk model based on the NASA rotor 37 in order to promote the reproducibility of results