The measurement results of various nitrile butadiene rubber (NBR) O-Ring sizes are presented, and reduced-order models are developed in order to predict the stiffness and damping coefficient as a function of O-Ring geometry, Shore hardness, squeeze, and excitation frequency. The results show that the curvature ratio d/D needs to be considered in the reduced-order models. The assessment of the model suggests a maximum deviation of 30% in predicted stiffness compared to the measurement data. However, taking into account the typical Shore hardness tolerance given by O-Ring manufacturers and other measurement uncertainties, the proposed model enables the prediction of various O-Rings with a good accuracy in the frequency range of 1.5–3.75 kHz, which corresponds to typical gas bearing supported rotor applications.
Herringbone-grooved journal bearings (HGJBs) for high speed turbo-machinery are often supported on O-Rings due to their favorable stiffness and damping characteristics for stability and alignment reasons. They yield, however, limited lifetime at high temperatures, insufficient assembly repeatability and dynamic characteristics that are difficult to measure and to tune. In order to overcome these shortcomings, a parametric model has been developed with the aim to design a flexible membrane bushing support that offers tunable tilting and radial stiffness and that can be coupled to various concepts to provide suitable damping levels to support a gas lubricated bearing bushing. Three damping concepts have been investigated that offer independent tuning of the support damping coefficient in combination with the novel flexible bearing bushing support. The new flexible membrane support was manufactured and its stiffness in radial and tilting direction measured before it was successfully implemented into a prototype.
This paper presents the results of a theoretical and experimental investigation of the potential of enhanced groove geometries to increase the bearing clearance of a HGJB supported rotor. The theoretical study investigates various groove geometries of different complexity and their effect on the stability threshold of a particular rotor geometry. The theoretical results obtained from a rigid-body rotordynamic model suggest an increase of more than 300% in instability onset speed when enhanced groove geometries are used compared to a classical, helically grooved rotor featuring the same radial bearing clearance. As part of the experimental investigation, one rotor shaft with classical grooves, representing the baseline rotor, and four rotors of identical diameter and clearance, but featuring enhanced grooves of varying degrees of complexity, were manufactured and experimentally tested. Good agreement between the experimentally determined speed of instability onset and the prediction was found for the investigated enhanced groove patterns. Experimental results of the classical rotor suggest the onset of instability to occur at a rotational speed of 56 krpm, whereas a speed of 180 krpm was achieved when enhanced groove geometries were applied to the rotor, which agrees very well with the theoretically predicted results and confirms the potential of enhanced groove geometries to stabilize HGJBs. Furthermore, the rotor featuring only a varying groove angle along the rotor axis was found to perform similarly to fully enhanced grooves of varying groove width, depth and angle, hence representing a good trade-off between performance increase and design cost.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.