Modal testing of a turbofan case using the LMIF

In this paper, part of the data collected during the modal survey of a turbofan case is used to assess the performance of a new mode indicator function able to locate the double radial modes. The new L-values Mode Indicator Function (LMIF) is based on the pivoted QLP decomposition of the measured Frequency Response Function matrices at discrete frequencies. For freely supported cyclic structures, the radial modes rotate with the largest amplitude at the input point. This allows testing with only one excitation point.