Design of Test Rig for Rotordynamic Simulations of Vertical Machines
2012 (English)Conference paper, Presentation (Refereed)
Most of the applications for fluid film bearings have horizontally oriented rotors. This has led to commercial software developers using algorithms and calculations for bearing properties based on 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, magnetic pull forces etc. Large hydropower units generally have vertically oriented shafts. In such systems with vertical rotors, there is no predetermined operating point. This paper presents the design of a test rig that was built at Vattenfall R&D during 2010-2011 in order to study and compare dynamic behaviour of vertical and horizontal rotors. The test rig consists of two bearings and a Jeffcott rotor. The bearings are 4-pad tilting-pad bearings and the operating speed of the test rig is from 0 to 3000 rpm. Radial load and shaft displacement are measured at each bearing using strain gauges and inductive displacement sensors. In the test rig presented in this paper, the excitation of shaft motion is self-induced, i.e. the shaft motion is caused by dead weight of the rotor and applied mass unbalance. Initial tests were performed in order to evaluate the test rig and differences in behaviour between bearing properties when the test rig is in vertical and horizontal position. Results from initial tests indicate that the bearing load - shaft eccentricity ratio is independent of the type of eccentricity, static or dynamic. In vertical operation at high dynamic eccentricities the load and eccentricity orbits have rectangular shapes due to the difference in stiffness for load on pads and load between pads. For vertical rotating systems using tilting pad bearings with a low number of pads and operating at high dynamic radial loads, the bearing properties can possibly cause excitation of natural frequencies at n times the nominal speed, where n is the number of pads.
Place, publisher, year, edition, pages
Research subject Solid Mechanics
IdentifiersURN: urn:nbn:se:ltu:diva-35923Local ID: aa8349e0-4ace-409f-9901-b0a037d93a1fOAI: oai:DiVA.org:ltu-35923DiVA: diva2:1009177
International Symposium on Transport Phenomena and Dynamics of Rotating Machinery : 27/02/2012 - 02/03/2012
Godkänd; 2013; 20130204 (andbra)2016-09-302016-09-30Bibliographically approved