Dynamic Investigation on a Pelton Runner: FEM Calculation and Experimental Results

Abstract

The dynamical phenomena involving a Pelton runner during normal operation are getting more and more of concern in the design of such kind of turbines. In fact, the increasing of the performance required by the market imposes runner designs that can become critical from a structural point of view. Each bucket is subjected to a certain number of impulses per revolution corresponding to the number of nozzles. This high frequency load could lead to a strong dynamic response of the runner if some kind of resonance takes place. For these reasons, an accurate modal analysis is to be performed before the runner realization, in order to avoid any crack arising during operation. This paper describes how a new, high performance profiled Pelton runner was modeled and dynamically calculated by FEM code ANSYS in order to obtain its natural frequencies and mode shapes. Subsequently, the modal behavior of the runner was experimentally investigated by means of an impulse test on field. The natural frequencies were got by examinating the FFT of the response and the mode shapes were reconstructed according to the stored signals of the accelerometers. The match between the experimental and numerical data was pretty good.