Oil-free Bearing Research Articles

Identification of Dynamic Force Coefficients for an Additively Manufactured Hermetic Squeeze Film Bearing Support Damper Utilizing a Pass-Through Channel

Abstract The following paper presents breakthrough experimental results for a new hermetic squeeze film damper (HSFD) concept that is integrally designed within an externally pressurized tilting-pad radial gas bearing support. The flexibly damped gas bearing module was designed for a 7.2″ (183 mm) diameter shaft and fabricated using direct metal laser melting (DMLM); also known as additive manufacturing. The bearing and HSFD were sized based on ongoing studies for oil-free supercritical carbon dioxide (sCO2) power turbines in the 8.5 MW–10 MW power range. The development of the new damper concept was motivated by past dynamic testing on HSFD, which generated frequency-dependent stiffness and damping force coefficients. In efforts to eliminate the frequency dependency, a new HSFD architecture was conceived that adds accumulator volumes and a pass-through channel to previously conceived HSFD flow network designs. The other motivation for the work is the need to develop a cost-effective and reliable oil-free bearing technology that is scalable to large power turbomachinery applications. There were several objectives for the following work. The first objective was to successfully design and fabricate a single piece bearing-damper using additive manufacturing, while dimensionally controlling critical design features. The paper discusses the manufacturing steps and shows cut-ups that reveal adequate clearance control capability with internal damper clearances. The second objective was to perform experimental testing with the new HSFD design in efforts to extract stiffness and damping coefficients for excitation frequencies within 20–160 Hz and peak vibration amplitudes between 0.25 mils (6.35 microns) to 1 mil (25.4 microns). The test results for a single HSFD bearing module indicated that the design modifications to the HSFD architecture were successful in eliminating nearly all the frequency dependencies for the stiffness force coefficient. The dynamic tests yielded a stiffness coefficient that varied between 112 klb/in. (19.6 MN/m) and 96 klb/in. (16.8 MN/m). The damping force coefficient however, exhibited relatively more variation with frequency with values residing between 175 lb-s/in. (31 kN-s/m) to 214 lb-s/in. (37 kN-s/m). Finally, the paper advances a three-dimensional fluid-structure interaction (FSI) model using transient finite element analysis (FEA) coupled to a computational fluid dynamics (CFD) model. The FSI analysis performed between 20 Hz and 80 Hz was used to predict the stiffness and damping of the HSFD using a quarter-section model of the damper. The FSI analysis was able to support test results by showing only a 6–7.4% change in the magnitude of force coefficients. Stiffness predictions agree reasonably well with experiments whereas damping is underpredicted.

Анализ развития безмасляных подшипниковых систем быстроходных компрессорных и энергетических агрегатов роторного типа для мобильных условий эксплуатации

The article considers an analysis of prospects for the use of oil-free bearings for working conditions in rotary units of autonomous mobile installations. The analysis made it possible to establish the current level of development of oil-free bearing technologies, the existing limitations of their use in units of autonomous mobile installations and urgent problems, the solution of which requires research and further improvement of the designs of bearing units.

Selection of the oil-free bearing system for a 30 kW ORC microturbine

The article discusses results of the analyses of various bearing systems for the rotor of an ORC (Organic Rankine Cycle) microturbine with an electric power of 30 kW. It is impossible to choose the appropriate bearing system taking into account only basic parameters of the bearings. When designing a new power turbine, it is important to conduct the dynamic and strength analysis of the entire rotor-bearings-supporting structure system. The nominal rotational speed of the newly designed single-stage axial-flow turbine is 40,000 rpm. The turbine will be powered using the vapour of a low-boiling working medium. The chosen working medium cannot be used in combination with all materials that are commonly used for turbine constructions. An additional requirement was that the turbogenerator must be oil-free. The temperature of the working medium directed to the rotor blades could exceed a value of 200 °C. Three bearing systems were considered: bearings lubricated with a low-boiling fluid (in the liquid form), gas bearings lubricated with the vapour of a low-boiling medium and rolling bearings. Since the rotors used in those three systems have different geometries, their dynamic properties vary as well. The rotor dynamics analyses were carried out using computer programs belonging to the MESWIR environment, which had been developed at the Institute of Fluid-Flow Machinery of the Polish Academy of Sciences (IMP PAN) in Gdańsk. The computational model, based on the finite element method, was used to prepare graphs on which are presented vibration amplitudes as functions of the rotational speed. The computational model, based on the finite element method, served to perform calculations on the basis of which graphs presenting vibration amplitudes as functions of the rotational speed were prepared. Moreover, vibration trajectories of individual nodes of the computational model were shown. Besides analyses of the bearings themselves, calculations were also carried out to assess the dynamic properties of the rotors supported by those bearings in a wide range of rotational speeds. As a result of the conducted analyses, the concept of an innovative turbogenerator was created. Its rotor can operate at a very high rotational speed, and the bearings do not require oil lubrication.

High-Speed Hermetic Turbogenerator with a Hybrid Bearing System

In the power industry, the most commonly used hydrostatic bearings are usually oil lubricated. On the contrary, for a distributed combined heat and power production, in the working machine—a hermetic high-speed turbogenerator—an oil-free bearing system is required. For this purpose, hydrostatic bearings lubricated with an organic, oil-free working fluid have been designed. Characterized by its limited lift force, hydrostatic bearing system can be used in small-power turbomachinery. To expand the functionality of the application, a new type of bearing—a hybrid bearing—was designed, built, and tested. In this new bearing, both hydrostatic and hydrodynamic effects are combined. In addition, a magnetic thrust bearing has been designed, so that the whole hybrid bearing system is characterized by hydrostatic, hydrodynamic, and magnetic effects. To confirm the good stability of rotor dynamics, numerical calculations and experimental tests have been conducted. The presented design resulted in good bearing lift and reliability of the bearing system.

Oil-free bearing development for high-speed turbomachinery in distributed energy systems – dynamic and environmental evaluation

AbstractModern distributed energy systems, which are used to provide an alternative to or an enhancement of traditional electric power systems, require small size highspeed rotor turbomachinery to be developed. The existing conventional oil-lubricated bearings reveal performance limits at high revolutions as far as stability and power loss of the bearing are concerned. Non-conventional, oil-free bearings lubricated with the machine working medium could be a remedy to this issue. This approach includes a correct design of the machine flow structure and an accurate selection of the bearing type. Chosen aspects of the theoretical and experimental investigations of oil-free bearings and supports; including magnetic, tilting pad, pressurized aerostatic and hydrostatic bearings as well as some applications of oil-free bearing technology for highspeed turbomachinery; are described in the paper.

Developing of Computational Investigation Methodology of Newtonian Fluid in the Crescent-shaped Gap of Turbogenerator Oil-free Bearing

The paper suggests the methodology of computational investigation of fluid and gas flow in the crescent-shaped gap of turbogenerator oil-free bearing on the basis of ANSYS CFX package. Numerical computation data have good convergence with empirical results obtained by other scientists for the same objects. Verification data prove the possibility of computational methodology implementation, at the first stage, in a limited sphere of engineering applications, particularly, when designing cooling systems for eccentric annulus of oil-free friction assemblies.

Performance of a Foil-Magnetic Hybrid Bearing

Abstract To meet the advanced bearing needs of modern turbomachinery, a hybrid foil-magnetic hybrid bearing system was designed, fabricated, and tested in a test rig designed to simulate the rotor dynamics of a small gas turbine engine (31 kN to 53 kN thrust class). This oil-free bearing system combines the excellent low and zero-speed capabilities of the magnetic bearing with the high-load capacity and high-speed performance of the compliant foil bearing. An experimental program is described which documents the capabilities of the bearing system for sharing load during operation at up to 30,000 rpm and the foil bearing component’s ability to function as a backup in case of magnetic bearing failure. At an operating speed of 22,000 rpm, loads exceeding 5300 N were carried by the system. This load sharing could be manipulated by an especially designed electronic control algorithm. In all tests, rotor excursions were small and stable. During deliberately staged magnetic bearing malfunctions, the foil bearing proved capable of supporting the rotor during continued operation at full load and speed, as well as allowing a safe rotor coastdown. The hybrid system tripled the load capacity of the magnetic bearing alone and can offer a significant reduction in total bearing weight compared to a comparable magnetic bearing.