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The operators of electric power plants are interested in having at its disposal a rapid and reliable tool that provides condition monitoring as well as fault detection (unbalance, bow, cracks, etc.) and diagnostics for its rotating machinery. Monitoring machine vibrations is a major concern for any operator in order to ensure safety by preventing machine failure and scheduling any necessary maintenance. In the present paper a model based approach is used to balance a large steam turbo-generator unit experiencing high amplitude vibration levels. Such approach combines a finite element model for the shaft-bearing-support system and vibration measurement acquired on the real machine in order to identify the appropriate solution for balancing. Rotor lateral position is monitored using displacement probes mounted close to the bearings location combined to seismic transducers mounted on the bearing casing. Several vibration datasets, measured by the displacement probes and corresponding to different operating regimes of the machine, are used for fault detection. The results obtained from these analyzes are then used to balance the machine and thus reduce vibration levels.

An experimental investigation of the parameters controlling the whistling frequency and amplitude of an orifice in a confined turbulent flow is undertaken. A circular single hole orifice with sharp edges, a hole diameter equal to 0.015 m and a thickness equal to 0.005 m, is arranged in an air test rig with an inner diameter equal to 0.03 m. The Mach number ranges around 0.02 and the Reynolds number around 10(4). Variable reflecting boundary conditions are arranged upstream and downstream, and several flow velocities are tested. It is found that the Bode-Nyquist criterion accurately predicts the conditions of self-sustained oscillation and the value of the whistling frequency. Furthermore, it is found that the acoustic velocity in whistling regime varies from 1% to 15% of the steady flow velocity, and that it depends on the overall acoustic reflection of the surrounding pipe and on the Strouhal number.