Full three-dimensional investigation of structural contact interactions in turbomachines

Abstract

International audienceMinimizing the operating clearance between rotating bladed-disks and stationary surrounding casings is a primary concern in the design of modern turbomachines since it may advantageously affect their energy efficiency. This technical choice possibly leads to interactions between elastic structural components through direct unilateral contact and dry friction, events which are now accepted as normal operating conditions. Subsequent nonlinear dynamical behaviors of such systems are commonly investigated with simplified academic models mainly due to theoretical difficulties and numerical challenges involved in non-smooth large-scale realistic models. In this context, the present paper introduces an adaptation of a full three-dimensional contact strategy for the prediction of potentially damaging motions that would imply highly demanding computational efforts for the targeted aerospace application in an industrial context. It combines a smoothing procedure including bicubic B-spline patches together with a Lagrange multiplier based contact strategy within an explicit time-marching integration procedure preferred for its versatility. The proposed algorithm is first compared on a benchmark configuration against the more elaborated bi-potential formulation and the commercial software Ansys. The consistency of the provided results and the low energy fluctuations of the introduced approach underlines its reliable numerical properties. A case study featuring blade-tip/casing contact on industrial finite element models is then proposed: it incorporates component mode synthesis and the developed 3D contact algorithm for investigating structural interactions occurring within a turbomachine compressor stage. Both time results and frequency-domain analysis emphasize the practical use of such a numerical tool: detection of severe operating conditions and critical rotational velocities, time-dependent maps of stresses acting within the structures, parameter studies and blade design tests

Nonlinear vibrations of a misaligned bladed Jeffcott rotor

“…Legrand et al [11] also provided complete finite element model that describes contacts between the blades and casing due to modal interaction of each structure combined with small clearances. Legrand et al [12] developed another model with three dimensional kinematics of the contact phenomenon by using the Lagrange multiplier and B-splines of the contact surface. Jacquet-Richardet et al [13] gave a review of these models and results which synthesize blade tiprub interaction and rotor-to-stator contacts.…”

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] .…”

Anti-Optimisation Applied to the Analysis of Rotor/Stator Interaction

“…These simulations are carried out based on the strategy presented in [16], that was applied in [3] and is briefly recalled here for the sake of clarity. For a definition of variables see the Nomenclature at the end of this paper.…”