Excitation of nodal diameter mode-shapes of a stator ring of a turbojet engine using a limited number of excitation sources

When considering engine tests, the sensors used to monitor the rotor parts mainly consist in strain gauges whose information is very sensitive to the gauge positioning, especially in high stress gradient regions. Therefore, to reduce the risk of misinterpreting the response given by the gauges, their calibration is required. Because strain gauges are positioned so that specific modes will be monitored, their calibration must be carried out for these modes. For cyclic symmetric structures, their high spectral density imposes the use of dedicated calibration techniques. In the present paper, the concept of modal appropriation is investigated as the first step of the calibration procedure.
This paper aims at presenting the development of an experimental approach enabling the isolation/appropriation of specific nodal diameter modes of a stator stage of an axial compressor using a limited number of excitation sources. A special emphasis has been brought to the minimum number and the optimized location of the excitation sources (shakers) required in laboratory conditions to appropriate specific nodal diameter modes and thereby retrieve the related modal features needed for the gauges calibration and mechanical design.