Jan Kiciński

Influence of the flow prehistory in the cavitation zone on the dynamic characteristics of slide bearings

Abstract A theoretical model of the cavitated zone and the equation describing the oil flow in this zone are presented in this paper. This equation allows one to determine the boundaries of the cavitated lubricating film by taking into account the influence of the time history of the flows on their balance. The Reynolds equation is then integrated for the boundary conditions determined. The numerical calculations were carried out for the case of periodically varying external loads and large oscillations of the journal centre. The results of the theoretical calculations were compared with experimental data.

EFfect of the aeration of a lubricating oil film and its space- and time-related compression on the static and dynamic characteristics of journal bearings

Abstract A theoretical model of an aerated lubricating oil film with the form of an air-in-oil emulsion is presented in this paper; a method for describing it mathematically is given. The appropriately modified Reynolds equation describes the pressure distribution in the emulsion, both in the positive and in the negative pressure zones, without the need to apply any additional boundary conditions for the end of the positive pressure zone. The static and dynamic characteristics of a bearing, calculated on the basis of the model presented, were compared with results obtained on the basis of the classical model (pure oil) and the Reynolds boundary condition. An attempt to consider in the calculations a space- and time-dependent compression of the aerated oil film, interpreted as space- and time-related variations in the air-in-oil emulsion density, is also presented.

The influence of selected design and operating parameters onthe dynamics of the steam micro-turbine

Abstract The topic of the article is the analysis of the influence of selected design parameters and operating conditions on the radial steam micro-turbine, which was adapted to operate with low-boiling agent in the Organic Rankine Cycle (ORC). In the following parts of this article the results of the thermal load analysis, the residual unbalance and the stiffness of bearing supports are discussed. Advanced computational methods and numerical models have been used. Computational analysis showed that the steam micro-turbine is characterized by very good dynamic properties and is resistant to extreme operating conditions. The prototype of micro-turbine has passed a series of test calculations. It has been found that it can be subjected to experimental research in the micro combined heat and power system.

Experimental investigation of the ORC system in acogenerative domestic power plant with a scrollexpanders

Abstract The paper presents the results of experimental investigations of the ORC system with two scroll expanders which have been used as a source of electricity. Theworking fluidwas HFE7100 – a newly engineered fluid with a unique heat transfer and favourable environmental properties. In the ORC system three heat exchangers were used (evaporator, regenerator, condenser) and before expanders the droplet separator was installed. As a source of heat an innovative biomass boiler was used. Studies have been carried out for the expanders worked in series and in parallel. The paper presents the thermal and fluidflow properties of the ORC installation for the selected flow rates and different temperatures of the working medium. The characteristics of output electrical power, operating speed and vibrations for scroll expanders were also presented.

Numerical Model of the High Speed Rotors Supported on Variable Geometry Bearings

The reported investigations aim at developing the theoretical model of a bearing characterized by variable geometry. The method used for calculating the non-linear response to an arbitrary excitation takes into account factors characteristic of the variable bearing geometry, including friction in the supports. The article presents part of the study referring to numerical analyses oriented towards developing the model of a high-speed rotor supported on bump-foil or tilting pad bearings.

Assessment of Materials and Operational Imperfections in Rotating Machinery

Presented have been the methods of modelling of the selected materials and operational imperfections (defects) like rotor cracks and hydrodynamic instability in rotating machines. Despite abundant information on this topic, there are still numerous problems to be solved. This regards primarily to the analysis of characteristic symptoms of such defects in the form of e.g. nonlinear vibrations and coupled forms of lateral, axial and torsional vibrations. The paper presents also author’s opinions concerning the one of the most intriguing operational imperfections, namely the formation of oil whirls and oil whips in slide bearings of a rotating machine. Coupled forms of vibration are generally a result of different kinds of couplings taking place in the system and interactions between construction and material imperfections.

Thermal Studies on Foil Bearings with a Sliding Coating Made of Plastic Material

The article presents the study of thermal phenomena that accompany the foil bearings operation. Tests were carried out on a specially designed high speed test rig, using a multi-channel measurement system and a thermal imaging camera. The object of the study was a 2nd generation gas foil bearing. In order to reduce the sliding friction, the top foil was covered with specially selected plastic and was operating with the journal covered by a layer of ceramic. The study was conducted at different speeds in which the temperature of the top foil was measured at several points spaced around the circumference of the bearing. In addition, the temperature distribution was analyzed on the outer surfaces of the bearing by means of the infrared camera. On the basis of the results, it was examined how rotational speed affects the temperature of foil bearing elements. The maximum temperature that can occur at steady operational conditions was also determined.

New method of description of dynamic properties of slider bearings

Abstract A method for the calculation of the dynamic characteristics of slider bearings is presented. It is based on a two-dimensional model of flow within the continuous and cavitated zone of the lubricating film. A method for taking into account the prehistory of the system is presented. Such a method enables the calculation, without the usual simplifying assumptions, of the trajectories of the centre of the journal when it is strongly dislocated. The results of the theoretical investigations of the range of validity of the proposed description are presented. Some examples of the calculated trajectories of specific bearings of combustion engines are given.

Analysis of the Rotor Supported by Gas Foil Bearings Considering the Assembly Preload and Hardening Effect

This article discusses a new method for modelling elastic deformations of a foil bearing’s structure, taking into account key phenomena influencing its characteristics. Special attention was paid to the assembly preload, which has an impact on the stiffness of the supporting system and thus also on the static and dynamic properties of the rotor. There has been proposed the method which allows for the inclusion of a selected preload into the bearing model. A new FEM model of the foil bearing’s structure has been described. This model was coupled with an in-house developed flow model of the bearing and the entire rotating system. Computations were made for several assembly preload values, taking into account changes in the bearing structure stiffness as the load increases. The changes in stiffness associated with the load changes were due to the nonlinear geometry of the foils, and also due to the contact phenomena, including friction between components. The applied calculation algorithm allowed to take into account all these phenomena. The results obtained using the developed model confirm the very high influence of the foil bearing’s pre-clamp and the progressive stiffness on the properties of the rotating system. Numerical models of this type can pave the way for a further development of foil bearings and for their wider use in modern high-speed fluid-flow machines.

The Dynamics of the Laboratory Rotor Founded on the Gas Foil Bearings—Numerical Analysis

The paper presents a fragment of the investigations on the gas foil bearings modeling, which were made out in the Institute of Fluid Flow Machinery (IMP PAN). The calculations are carried out in the S-MESWIR system of computer codes, originally invented in the IMP PAN and with the use of commercial software. A two-bearings laboratory rotor of about 3.5 kg weight is proposed. It is modeled in the S-MESWIR system with the use of beam finite elements. It is dynamically forced with the unbalance. The properties of the bearings are defined with the FE model of foil set. The air was assumed as a lubricating gas. For low speeds the gas layer may be not developed because the aerodynamic effects between the bearing journal and the top-foil are too weak. Thus the rotor is supported on the foils only. For higher values of rotational speed a gas film was fully developed and it takes part in the carrying of the load. The paper presents the example how the modification of the structural layer properties (especially stiffness) can change the dynamic characteristics of the rotating system.