Impeller Modal Testing Based on Measuring Points Optimization and Acceleration Sensors

Since torpedo turbine impeller is small and light, the number of acceleration sensors has a direct effect on testing precision and measured order of impeller modal. In order to reduce the number of testing points for the purpose of decreasing the effect of additional mass on the natural frequency of the impeller, modal confidence analysis is carried out by introducing the finite element grid model and the modal calculation result of the impeller into the software LMS Virtual.lab. The response number and positions of the measuring points, as well as the position and direction of the excitation point, in impeller modal testing are optimized. The first 3 orders of natural frequency and vibration modes of the impeller are identified with acceleration sensors on the basis of pre-test. The vibration modes of the modals from testing coincide with that from calculation, and the maximum error of natural frequency is 3.3%. This research indicates that the optimized position and number of sensors can improve modal testing effect, but cannot eliminate the influence of additional mass on the natural frequency of the impeller completely. It is suggested that the non-contact laser vibrameter technology be employed to obtain more accurate impeller modal parameters.