Rotordynamic Evaluation of Full Scale Rotor on Tilting Pad Bearings With Integral Squeeze Film Dampers

Abstract

In the last 10 years, major centrifugal compressor manufacturers have been investing in developing technologies to improve their products. Following the increasing demand in terms of performance, efficiency and compactness, the current trend in the compressor industry is to increase the “power density”. One big challenge of this “power density” approach is the increase of the rotational speed which may be related to rotordynamic concerns (e.g. crossing of higher rotor modes, stability). Commonly used in the aircraft gas turbines [16], the squeeze film dampers represent an efficient solution to deal with high vibrations and to ensure stable operation for supercritical rotors. In the Oil & Gas Centrifugal Compressors world, SFDs are not so often utilized by the manufacturers but sometimes chosen by the end users as a retrofit solution when high level of synchronous/sub-synchronous vibrations are experienced in the field. The experimental activities described in this paper represent the authors’ Company effort to validate the behavior of a special, integrated SFD type in order to add this component in the available technology portfolio of a centrifugal compressor using it since the design phase. To accomplish this target, the SFD testing was performed originally at the component level and finally at a system level on a “dummy rotor”, specifically designed to mimic the rotordynamic behavior of a real rotor (e.g. running across both the two first rigid modes and the first bending mode). The main objectives of the testing activity were: to check the benefit of using SFDs in order to increase the rotor system damping, to check the SFD overall operational performances, and finally to validate the rotordynamic predictability of this new rotor system. The system level testing program was performed in a high speed balancing bunker where the rotor was equipped with a magnetic exciter able to deliver sub-synchronous excitation. The main test results which will be described in details in the paper are anticipated here. SFDs showed a significant increase in the damping of rigid modes compared to a baseline configuration (rotor running on traditional journal bearings); the SFDs behavior was fully assessed both from rotordynamic viewpoint (rotor and damper housing vibrations) and from operational viewpoint (oil temperature and pressures directly measured in the damper land); finally the rotor modal damping identification techniques are applied to this highly damped rotor system in order to compare the experiment with the relevant predictions. As a conclusion the testing activity provided the authors’ Company with confidence in the use of this integrated SFD technology and enabled a new option for centrifugal compressor design.

A Systematic Approach to Estimate the Impact of the Aerodynamic Force Induced by Rotating Stall in a Vaneless Diffuser on the Rotordynamic Behavior of Centrifugal Compressors

“…Within this scenario, the proposed approach could provide some useful For example, the use of squeeze film dampers (SFDs) in the same machine was hypothesized: the SFDs are a powerful device used to increase the rotor damping, since their working principle is indeed to provide a low stiffness level of the supports to maximize the oil damping effect [26]; as a reference value, the logarithmic decrement of the rotor first mode is increased from 0.28 to 0.99, according to an AP1617 level 2 stability analysis [27] when SFDs are adopted.…”

Numerical and Experimental Stability Investigation of a Flexible Rotor on Two Different Tilting Pad Bearing Configurations

“…Since the term is nonsingular, it is invertible. Solving (17) to obtain the estimated parameters vectorp…”

“…Squeeze film dampers have been widely used to improve the stability of rotor. Gerbet et al [17] carried out the rotordynamic evaluation of a full scale rotor on two tilting pad bearings with integral squeeze film dampers. Besides the experimental damping ratio identification to assure the stability of rotor in operating conditions, many researchers including Gupta et al [18] and Dimond et al [19] investigated how to predict the stability of the rotor by an analytical method.…”