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International audience; The main purpose of this paper is to present an experimental setup dedicated to the study of high speed interactions such as those occurring between the rotating blade and the casing of an aircraft engine compressor. A simplified approach of rotor/stator interaction was experimentally simulated for ranges of velocities and interaction depths varying from 60 m/s to 270 m/s and from 0.13 mm to 0.35 mm respectively. Only high speed orthogonal contact were studied. The device was made up of a ballistic bench projecting a sample of abradable material (M601) against an instrumented tool (Steel 42CrMo4) representing the simplified blade shape. In order to increase significantly the measurement system bandwidth and to measure accurately the high speed interaction forces, a correction method based on the principle of modal analysis was developed and successfully employed. This work provides new experimental data regarding the material behavior of M601 in high speed orthogonal cutting conditions. They were in good agreement with those already observed in the literature for velocities up to 100 m/s. These new results showed the non-linear increase of the mean interaction force with the velocity and incursion depth for the large range of velocities considered in this present work. Post-experiment observations gave evidence of two wear mechanisms: cutting and plastic deformation.

International audience; Aircraft engine manufacturers are developping a new generation of turbojet engines featuring a lower impact on the environment, increased performances as well as reduced gas consumption. The efficiency of an engine is mostly driven by the operating clearance between the rotating parts and the stator. Accordingly, modern designs focus on the minimization of these clearances. In this context, unavoidable rotor imbalances or mistuning stemming from manufacturing processes as well as distortions resulting from thermal expansion or assembly conditions may generate blade-tip/casing contacts that are now considered as non-accidental operating conditions. In order to minimize the consequences of such events, an abradable coating is sprayed along the inner surface of the casing and acts as a fuse when the blade and the casing are in contact. However, even when an abradable coating is used, significant structural damages and wear as well as blade failures have been witnessed experimentally. The understanding of the physical phenomena at play called, on one hand, for throrough experimental investigations of rotor/stator contacts on full-scale stages of compressors and underlined that blade failure is mainly due to vibratory fatigue although the abradable coating is worn. On the other hand, numerical simulations have been performed to better understand the blade dynamics: over the last decade Snecma and its academic partners jointly developed a code for the simulation of COntacts between ROtor and Stator: COROS. This code allows for the simulation of contacts—with a Lagrange multiplier contact treatment procedure—between full 3D models of engine components and accounts for abradable coating material removal. In particular, the simulation of experimental setups with COROS highlighted the correlation between the blade vibratory response and the abradable material removal. Yet still an experimental code, this paper addresses the integration of COROS within the design process of aircraft engine blades at Snecma. The paper focuses on ongoing research for the identification of critical parameters in the arising of interactions as early as the design stage of components. A particular attention is paid to the mechanical properties of the abradable coating for which both experimental and numerical investigations are detailed.

International audience; The purpose of the present paper is to study interaction phenomena between an abradable material (M601) and a titanium alloy (TA6V). This interaction which can occur in an aircraft engine when the rotating blade tips rub on the compressor casing, is analyzed on an experimental laboratory set-up. Only orthogonal cutting conditions are considered in this preliminary study to monitor the load evolution with velocity. The experimental results obtained for a range of velocities $10 < V < 10^7$ m/s and for a range interaction depth $0.05 < t_1 < 0.5$ mm are presented. After analysis of measurements, the mean interaction force increases proportionally to the interaction depth increment. The effects of the contact geometry on the loads, especially the radius of the edge, are investigated. The increase of the radius value for a given interaction depth increases the load value.This work provides new basic data for behaviour laws introduced in numerical models simulating the interaction between the blade tip and the compressor casing in turbine engine applications. Original high-speed photographs recorded in real time during the process illustrate the chip separation by brittle manner. A temperature field in the abradable material will be able to be obtained for only a low speed of 5 m/s.

International audience; Higher aircraft energy efficiency may be achieved by minimizing the clearance between the rotating blade tips and respective surrounding casing. A common technical solution consists in the implementation of an abradable liner which improves both the operational safety and the efficiency of modern turbomachines. However, unexpected abradable wear removal mechanisms were recently observed in experimental set-ups as well as duringmaintenance procedures. Based on a numerical strategy previously developed, the present study introduces a numerical-experimental comparison of such occurrence. Attention is first paid to the review and analysis of existing experimental results. Good agreement with numerical predictions is then illustrated in terms of critical stress levels within the blade as well as final wear profiles of the abradable liner. Numerical results suggest an alteration of the abradablemechanical properties in order to explain the outbreak of a divergent interaction. New blade designs are also explored in this respect and it is found that the interaction phenomenon is highly sensitive to (1) the blade geometry, (2) the abradablematerial properties and (3) the distortion of the casing.

Paper GT2012-68171Volume 7: Structures and Dynamics, Parts A and BConference Sponsors: International Gas Turbine InstituteISBN: 978-0-7918-4473-1; International audience; Higher aircraft energy efficiency may be achieved by minimizing the clearance between the rotating blade tips and respective surrounding casing. A common technical solution consists in the implementation of an abradable liner which improves both the operational safety and the efficiency of modern turbomachines. Recently, unexpected abradable wear removal mechanisms were observed in experimental set-ups and duringmaintenance procedures. The present study introduces a numerical strategy capable to address this occurrence. After focusing on the analysis of the experimental results, the good agreement between experimental observations and numerical results is illustrated in terms of critical stress levelswithin the blade as well as final wear profiles of the abradable liner. New blade designs are also explored in order to assess the impact of blade design on the outbreak of the interaction phenomenon. The prevalence of three dominant parameters in the interaction onset is shown: (1) blade design, (2) abradable material mechanical properties and (3) the need for a global distortion of the casing to synchronize blade-tip/abradable coating contacts.

International audience; In rotating machinery, notably in modern high efficiency compressors, a critical requirement for optimal performance consists in minimizing radial clearances between the rotating bladed disk and the casing. This solution significantly increases the risks of contact between rotating bladed disk and casing and may lead in specific conditions to catastrophic behavior (component failure, etc.). The physical phenomena and mechanisms involved in blade-casing contact interaction situations are still misunderstood. In order to highlight these mechanisms, specific experiments have been performed on an experimental multi-stage compressor of a turbojet with dedicated dynamic and thermal instrumentations. For all configurations tested, major damages are noticed: blades had cracks and the abradable coating of the casing was heavily machined. Results show that the blade failure refers to fatigue limit with first natural mode excitation of the blade. The paper is focused on the analysis of the successive stages of blade dynamic response before the failure. It is shown that this response is influenced by the variations of the blade-casing contact conditions. These conditions are linked to the thermomechanical behavior and wear of coating, illustrated by high thermal levels and non uniform wear profile. Coupling between thermomechanics, wear and dynamic has to be considered to highlight the transient mechanisms leading to the cases of blade failure.