Prediction of the Vibratory Behaviour of Monoblock Sectorised Stator Vanes

Abstract

Stator vanes which are found at different stages in axial compressors are subject to major aerodynamic load fluctuations, due to cyclic excitations induced by the wakes of the rotors located upstream and also due to the pressure waves generated by the blade rows located downstream. In a vibratory fatigue context, it is important to ensure the structural strength of these stator vanes. A new technology of monoblock sectorised stator vanes has been developed to provide an easier manufacturing process and lower costs; in return, cyclic symmetry properties, which make the prediction studies easier, are lost in this case. Besides, these kinds of monoblock sectors are characterized by low damping which increases the criticality of the blade modes localization. The division into sectors of stator vanes creates a high density of eigenmodes in some short frequency ranges; this phenomenon is accompanied by non-negligible modal participations of neighbouring eigenmodes. Moreover, stator vanes sectors have shown a strong sensitivity to mistuning, making their vibratory behaviour prediction more difficult by means of deterministic prediction methods. In this paper, a phenomenological approach is followed to quantify the mistuning. Thus, several sensitivity to mistuning numerical studies were performed. They allowed to have first results about the relative predictable errors that could be done, depending on the mistuning. Some engine tests were also performed with gauges-equipped stator vanes sectors.

Stochastic Behaviour of Mistuned Stator Vane Sectors: An Industrial Application

“…Indeed, eigenmode simulations have been performed for different mistuning patterns and the results have been compared to those obtained with the tuned model via the MAC criterion [1]. The results which can be found in [10] have shown that the modes located in the high modal density areas are really sensitive to mistuning. The forced response of a stator vane sector is consequently very difficult to predict because the eigenmode shape of some modes changes radically.…”

“…The details of these results can be found in [10]. The second part deals with the stochastic approach that has been implemented and its application on a simplified model.…”