Unilateral contact induced blade/casing vibratory interactions in impellers: Analysis for rigid casings

Abstract

This contribution addresses the vibratory analysis of unilateral-contact induced structural interactions between a bladed impeller and its surrounding rigid casing. Such assemblies can be found in helicopter or small aircraft engines for instance and the interactions of interest shall arise due to the always tighter operating clearances between the rotating and stationary components. The investigation is conducted by extending to cyclically symmetric structures an in-house time-marching based tool dedicated to unilateral contact occurrences in turbomachines. The main components of the considered impeller together with the associated assumptions and modeling principles considered in this work are detailed. Typical dynamical features of cyclically symmetric structures, such as the aliasing effect and frequency clustering are explored in this nonlinear framework by means of thorough frequency-domain analyses and harmonic trackings of the numerically predicted impeller displacements. Additional contact maps highlight the existence of critical rotational velocities at which displacements potentially reach high amplitudes due to the synchronization of the bladed assembly vibratory pattern with the shape of the rigid casing. The proposed numerical investigations are also compared to a simpler and (almost) empirical criterion: it is suggested, based on nonlinear numerical simulations with a linear reduced order model of the impeller and a rigid casing, that this criterion may miss important critical velocities emanating from the unfavorable combination of aliasing and contact-induced higher harmonics in the vibratory response of the impeller. Overall, this work suggests a way to enhance guidelines to improve the design of impellers in the context of nonlinear and nonsmooth dynamics.

Thermomechanical Component Mode Synthesis for Blade Casing Interaction Prediction

“…Such methods are already in use to study rotor-stator contact problems, e.g. central finite differences [21,3]. Harmonic methods are used to model perioddic steady-state phenomena and have been applied to study blade-root / disk contacts [22] and friction phenomena in general [23] .…”

“…It is now recognized that such phenomena have to be accounted for in the design in order to avoid premature maintenance operation and therefore excessive operational costs. Several investigations, both numerical [2,3] and experimental [4,5] are devoted to the modelling and understanding of such events. A detailed summary [6] lists recent studies regarding material, thermal and mechanical aspects of rotor-stator rubbing.…”

Towards Full 3D Numerical Simulation of Whirl Motions Stemming From Unilateral Contact Constraints in Aircraft Engines

“…(28). Also, more details with respect to the computation of K r (Ω) and the treatment of centrifugal effects may be found in [17].…”

“…Linear convergence A ROM of the full bladed disk is computed based on the methodology presented in [17]. Both centrifugal and gyroscopic effects are accounted for based on the methodology presented in this article.…”

“…11). The computed ROM thus allows for an efficient extension of the reduction procedure presented in [17] to gyroscopic effects. It also yields very efficient computations for linear applications (forced responses, modal analysis or time integration).…”