V2i @ Turbo Expo


This week, V2i will attend Turbo Expo Conference in Oslo to present its results related to stress calibration on stator blades using experimental SAFE diagram.

The abstract of the paper is given below. Please feel free to contact us for further information or to get the full article.


Stress calibration methodology of stator blades using experimental SAFE diagram

During full scale engine testing, the vanes of the booster stator stages are instrumented with strain gages to ensure their integrity throughout the test. To compensate the inaccuracy in the placement of the gages, these gages need to be calibrated.

As of now, calibration is performed using a set of strain gages placed at adequate locations. A shaker is used to excite the stator stage in the operational frequency range and calibration factors are computed between the gages. However, the high number of modes involved complicates the post-processing.

During nominal conditions, the stator stages are submitted to a specific excitation induced by the surrounding stages and it is therefore relevant to concentrate the post-processing on the modes which are the most likely excited.

A stator stage was provided by Safran Aero Boosters and is used as a case study in this paper. In this example, the most excited modes are the ones with a specific number of nodal diameters corresponding to the number of blades of the upstream stage.

This paper introduces an improvement of the calibration methodology to consider the dominant nodal diameter of the structure. The proposed calibration procedure and the search for optimal excitation set-up are detailed. To this purpose, the following points are addressed.

Multiple excitations are used to appropriate the targeted modes. A comparative study of different shaker types, of the number of excitation points and of their location is performed. Both stationary wave and rotating wave excitations are considered and compared.

Experimental modal analyses are performed using both accelerometers and strain gages. Post-processing techniques are developed to determine the nodal diameters of the identified modes. SAFE (Singh’s Advanced Frequency Evaluation) diagrams are computed from the experimental data and compared with the diagrams obtained numerically by finite elements computations. The experimental SAFE diagram is built by correlation between the measured modal data and pure sine waves. A criterion based on the MAC formula allows assessing the degree of correlation.

Calibration is achieved by comparing strain measurements taken on one gage installed on the engine and velocities measured using laser vibrometers. It allows reducing the impact of the instrumentation on the modal content.

The calibration factors obtained by the novel proposed procedure are compared to the ones given by the currently used methodology.

 Référence: GT2018-76709

Jérôme Ligot*, Sébastien Hoffait, Jean de Cazenove**, Frédéric Vallino, Jean-Claude Golinval***

* V2i, Liège, 4031, Belgium - j.ligot@v2i.be, s.hoffait@v2i.be

** Safran Aero Boosters, Milmort, 4041, Belgium, jean.decazenove@techspace-aero.be, frederic.vallino@techspace-aero.be

***University of Liège, Department of Aerospace and Mechanical Engineering, Structural Dynamics Research Group, Liège, 4000, Belgium, JC.Golinval@uliege.be