%0 Journal Article
%T Experimental and Numerical Simulation of Unbalance Response in Vertical Test Rig with Tilting-Pad Bearings
%A Mattias N£¿sselqvist
%A Rolf Gustavsson
%A Jan-Olov Aidanp£¿£¿
%J International Journal of Rotating Machinery
%D 2014
%I Hindawi Publishing Corporation
%R 10.1155/2014/309767
%X In vertically oriented machines with journal bearing, there are no predefined static radial loads, such as dead weight for horizontal rotor. Most of the commercial software is designed to calculate rotordynamic and bearing properties based on machines with a horizontally oriented rotor; that is, the bearing properties are calculated at a static eccentricity. For tilting-pad bearings, there are no existing analytical expressions for bearing parameters and the bearing parameters are dependent on eccentricity and load angle. The objective of this paper is to present a simplified method to perform numerical simulations on vertical rotors including bearing parameters. Instead of recalculating the bearing parameters in each time step polynomials are used to represent the bearing parameters for present eccentricities and load angles. Numerical results are compared with results from tests performed in a test rig. The test rig consists of two guide bearings and a midspan rotor. The guide bearings are 4-pad tilting-pad bearings. Shaft displacement and strains in the bearing bracket are measured to determine the test rig¡¯s properties. The comparison between measurements and simulated results shows small deviations in absolute displacement and load levels, which can be expected due to difficulties in calculating exact bearing parameters. 1. Introduction Difficulties arise when simulating vertical machines with tiling-pad guide bearings. The cause of this is that, in systems with vertical rotors, there is no predetermined operating point. In vertical machines such as hydropower units and pumps, it is the mass unbalance, the generator¡¯s properties, and the flow conditions in the turbine that determine the position of the rotor [1]. Commercial software uses algorithms designed for calculations of rotordynamic and bearing properties for machines with a horizontally oriented rotor. This means that the shaft has a set operating point in the bearing based on static radial loads caused by the dead weight of the rotor. Bearing properties from software for horizontal machines are calculated at a static eccentricity; these types of software cannot perform simulations of a vertical rotor¡¯s behaviour. Assuming isotropic bearing parameters, that is, setting and , it is only possible to determine half of the natural frequencies and that should thus be avoided [2]. Historically both numerical simulations and experimental studies in test rigs have been performed to evaluate properties of tilting pad bearings [3, 4]. Glienicke et al. [5] performed tests in a horizontal test rig
%U http://www.hindawi.com/journals/ijrm/2014/309767/