- Broadband excitation due to the aerodynamic forces and the friction ones acting at the surfaces of the rolling elements and randomly distributed in time. This kind of excitation has increasing amplitude with higher RPM, as well. The static characterization of the blade has been firstly performed by carrying out a modal analysis of it from the SLDV output data measured over a grid of 7x10 points on each blade excited via impact hammer. The sum of the measured FRFs, appropriately scaled, is reported in Fig. 3. Then a CSLDV test has been performed on the steady blade excited via impact hammer. In order to cover the whole surface of the blade the mirrors have been fed by sinewaves at the frequencies of 1.1 and 12 Hz (non integer multiple frequencies to achieve a Lissajous picture and sweep different positions over subsequent cycles). The operational deflection shapes of the structure have been recovered from a single shot measurement. Modal analysis could be performed on the unique FRF given by the ratio of the output vibration velocity and the input force (measured by the CSLDV and the hammer). In fact this FRF contains both the time and spatial information needed for the ODS reconstruction. However the modal analysis is not presented in this paper. The LDV output spectrum measured in CSLDV mode is reported in Fig. 3, superimposed to the EMA FRFs sum. The typical sideband structure is evident from the spectrum. The modal parameters extracted from the SLDV test are reported in Table 1 together with the ODS recovered with CSLDV. A zoom of the spectrum over the natural frequency position is reported in Table 1 for each ODS. Table 1 Blade modal parameters and CSLDV ODSs The sideband spectrum characteristic of each ODS is visible, except for the modes that are not sufficiently excited, i.e. 431 Hz, or for close modes, i.e. the ones in the region for 340 Hz. 4. Rotating characterization The dynamic characterization of the blade in rotating conditions has been performed by means of the TLDV method, in which it is possible to change the position of the measurement point in the rotating coordinate system by varying the amplitude and phase of the signals that drives the mirrors. This allows to track a single point or to measure sequentially on a grid of points in order to have the spatial information related to the structure ODSs. The blade has then been tested in TCSLDV fashion when rotating at different RPM steps. By synchronizing the continuous scan with the blade rotation, the Lissajous figure covered by the laser beam is illustrated in Fig. 4. 528
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