Identification of the Natural Vibration Modes of a Turbine Engine Fan Using One- and Three-Dimensional Laser Vibrometry ^†

Turbine engine discs operate at high speeds with heavy loads. Any failure may result in the engine stopping or being destroyed. Therefore, it is necessary to check the normal modes and determine the rotational speeds at which they may occur. The aim of this article is to present a method of non-contact measurement of normal modes using the single and three-dimensional modes. The test element is the isolated first compressor stage of the DGEN-380 miniature jet engine (minijet). The disc has the shape of a hollow truncated cone with large blades. Vibration measurements were carried out in a non-contact manner using a scanning Doppler vibrometer. The measurement was made in 1D and 3D mode. The 1D mode is simpler and easier to prepare. In 3D mode, the calibration of three scanning heads significantly complicates the measurement preparation, but allows researchers to obtain the deformation in three-dimensional space The summary shows the measured frequencies using both modes. The shapes of deformation are also summarized. It is described how close the 1D measurement is to the 3D mode and in what frequency range. Finally, it is shown to what extent it is possible to describe the nature of structural oscillations in the 1D measurement mode.