Marc Berthillier

Dynamic Study of a Structure with Flexion-Torsion Coupling in the Presence of Dry Friction

In aero engines, blade vibrations are frequently reduced by centrifugal flyweights, which exert a dry friction force per unit length under blade platforms. The response of this system to a periodic load has been analysed experimentally and theoretically. From a model having mode shapes similar to those of a blade, and a dry friction link per unit length, we show that the presence of the dry friction link is very effective in reducing vibrations for a range of excitation loads. The theoretical analysis is based on the Craig and Bampton mode synthesis, the rigid movement of the platform in its plane and the replacing of the linear dry friction link by several discrete parallel systems. Direct integration of the equations of motion is carried out by using the Newmark method. The comparison with experimental results is good. This method can easily be extended to more complex structures and shows that the dry friction link is effective when stick-slip occurs in the contact zone by limiting the energy provided to the system.

Turbine Mistuned Forced Response Prediction: Comparison With Experimental Results

It is currently a major challenge for aeroengines manufacturer to be able to predict early in the design process the dynamic response of bladed disk. To guaranty a good accuracy of prediction, it is necessary to define properly the excitation (unsteady aerodynamics) and to take into account some phenomenon such as mistuning. This paper proposes an application of Snecma prediction method for mistune forced response on an experimental test case. The method used is a component modes synthesis method similar to the one proposed by Castanier and Pierre in 1997 [1] and validated against experiment in [2]. Some improvement have been performed to take into account more accurately the centrifugal forces effects in the projection basis and to couple the method with unsteady Computational Fluids Dynamic (CFD) codes. It is now possible to use this method in an industrial process. The method is applied to a HP turbine representative case, for which experimental results are available. These experimental results have been obtained in a European Community funded project dedicated to forced response study [3]. Mistuning effects have been measured. Moreover, a full characterization, of unsteady aerodynamics, aeroelastic and structural dynamics aspects have been performed. The results obtained with the proposed method are then compared to the experimental one. This application shows the consistency of the method and its efficiency.Copyright

A Numerical Method for the Prediction of Bladed Disk Forced Response

A numerical method has been developed to predict the forced response of bladed disks due to a wake excitation from upstream blade rows. The structure is modelled by a 3D finite element mesh of a bladed disk segment. Using cyclic symmetry, this model provides a modal base for the rotating structure. The aerodynamic damping of the vibratory modes and the excitation pressures on the blades due to the propagation of upstream flow defects are computed separately using the same 3D unsteady Euler analysis software. A modal response solution of the aeromechanical system is then performed.This analytical methodology has been used to study the forced response of an experimental high pressure compressor blisk. The results are analysed and compared with actual rig tests.Copyright

Traitement d'impact fluide-solide par la méthode particulaire SPH: Application: ingestion d'oiseau par les turboréacteurs

ABSTRACT A SPH method has been developed for the simulation of soft impacts of a fluid on a structure. The SPH method is coupled to a finite element method using a slave-master contact impact algorithm. An implementation has been performed in the Castem-Plexus explicit code. It is applied to bird swalling simulation in a turboreactor engine. The final strains and deformed shapes of the turbine blades are correctly predicted and the computation times are reasonable enough to do industrial applications.