Implementation of a Rig Test for Rotor/Stator Interaction of Low-Pressure Compressor Blades and Comparison of Experimental Results With Numerical Model

In turbomachines, a way to increase the engine efficiency is the reduction of the clearance between the blade tip and the surrounding casing. Indeed, clearance reduction goes along with leakage flow reduction. Therefore, contacts between blades and casing are commonly accepted in turbomachines. This is the reason why the inner surface of the casing is covered by a coating called ‘abradable’ that can be worn out without damaging the blade. Unfortunately, in some specific cases, soft contacts between the blade and the abradable coating can lead to high amplitude vibrations. These vibrations are the result of synchronization between the engine rotation speed and the blade vibration mode. In this case, the blade wears the abradable coating according to a cyclic pattern. The combination of the synchronization and the wear can lead, in the worst cases to vibration amplification and blade damage.

The rig test presented hereafter is designed and built to investigate and test the soft blade-casing contacts in the conditions where blade mode and speed synchronization can occur. It fills the following constraints: simplification of the low-pressure compressor environment but realistic mechanical conditions, repeatability, ability to test several blade designs in short time and at low cost.

After the rig test description, the validation of its capability to reproduce the looked out phenomenon is presented. Then, a blade design study is conducted to compare their capability to undergo an interaction with the abradable while staying below an acceptable level of vibration. The rig test gives also the possibility to investigate different contact conditions. In addition, these experiments allow to refine and mature the phenomenon comprehension and to validate and fit a numerical tool of the blade-casing interaction model developed on another side.

The numerical tool considers a 3D finite elements model of low-pressure compressor blade with a surrounding rigid casing combined with a specialized model to take into account the effect of the wear of the abradable coating on the blade dynamics. Specificities of the numerical model are shortly presented. The numerical parameters that lead the phenomenon in the numerical model (contact stiffness, wear model and damping) and their fitting are discussed. A comparison between experimental and numerical results is presented showing a good agreement in terms of critical angular speed, blade dynamics, wear pattern and depth on the abradable coating. Finally, the consistency between predicted results by the simulation and experimental results on the relative criticality of different blade designs, regarding the rotor-stator interaction phenomenon, is presented.