Experimental modal analysis of disk-like rotor–stator system coupled by viscous liquid

Abstract

The vibrational behavior of a rotor–stator system coupled by a viscous liquid is investigated experimentally using a test bench with rotor and stator simplified as disks. The understanding of this vibration problem is of particular importance in the design of hydraulic machines such as Francis turbines, pump–turbines or hydraulic pumps, where the elastic rotor is coupled to the adjacent elastic stator by the intermediate water. The especially developed test bench enables high-resolution scan measurements of the rotor and stator disk vibrations by applying the modal analysis method in combination with the laser interferometer technique. We present the mode shapes, eigenfrequencies and damping factors measured over a large number of parameter combinations of the stator thickness, the rotor thickness, the clearance between rotor and stator as well as the rotation speed of the rotor. We identify and discuss fundamental vibration mechanisms of the system (for example, the characterization of varicose and sinuous modes, or the frequency split between co- and counter-rotating modes). The derived experimental results may serve as a benchmark for the validation of simulation models studying the linear vibration including effects of rotation, bias flow and viscous damping.