Michał Wasilczuk

Study of the Influence of Heat Convection Coefficient on Predicted Performance of a Large Tilting-Pad Thrust Bearing

Part of the heat generated by the shearing of the lubricating film during operation of a hydrodynamic bearing is transferred to the bearing components. In the case of the pad, which is usually fully submerged in the lubricating oil, heat is further transferred at the pad free walls to the oil by convection. This mechanism causes a thermal gradient in a pad and, consequently, its thermal deflection. In large hydrodynamic thrust bearings, thermal deflection of the pads is an important phenomenon influencing bearing performance. For such bearings, pad distortion can reach the level of hydrodynamic film thickness and can significantly change the bearing’s properties. In this paper, the study of the influence of the heat convection coefficient on the predicted performance of a large hydrodynamic thrust bearing is presented. Two sets of convection coefficients at the pad free surfaces are investigated with the use of thermo-elasto-hydrodynamic (TEHD) calculations. An analysis is carried out for the Itaipu hydro turbine thrust bearing with the outer diameter equal to 5.2 m, which is one of the biggest hydro power plants in the world. The results of the theoretical predictions are compared to the measured data collected during bearing operation.

Application of the fluid–structure interaction technique for the analysis of hydrodynamic lubrication problems

Fluid–structure interaction technique seems to be one of the most promising possibilities for theoretical analysis of lubrication problems. It allows coupling of different physical fields in one computational task, taking into account the interaction between them. In this article, two sets of fluid–structure interaction analyses focusing on the bearing performance evaluation are presented. One analysis was applied to a water-lubricated journal bearing and the other to a hydrodynamic thrust bearing lubricated with oil. Steady-state operation was considered in both cases. In the presented cases of fluid–structure interaction analyses, all important phenomena accompanying bearing operation are considered, e.g. lubricant flow, structure movements and their deformations as well as heat transfer in case of thrust bearing. The problems encountered during modelling are discussed in this article, as well as the results of calculations: hydrodynamic pressures, gap geometries or temperature profiles.

Simulation of large thrust-bearing performance at transient states, warm and cold start-up

The start-up of a large hydrodynamic thrust bearing of a vertical hydrogenerator is one of the most critical situations during the lifetime of a bearing. Hydrodynamic load capacity is low due to low speed and higher thermal deformations of the pad. A new approach to the simulation of a hydrodynamic bearing is shown in this article. A combination of finite elements method and computational fluid dynamics is used to perform the transient simulation of the bearing start-up. A bidirectional bearing of a pump-storage power plant is investigated. To show the potential advantages of the new method, a comparison of the warm and cold start procedure is presented. The thermal crowning of the bearing pad, oil film gap and other parameters of both cases are compared in this article.

Large hydrodynamic thrust bearing: Comparison of the calculations and measurements

Hydrodynamic thrust bearings, used to carry axial loads in heavily loaded shafts of water power plants hydro turbines, can reach outer diameters even exceeding 5 m. In such large objects scale effect could be observed. According to this, allowable bearing specific load assuring safe operation of the bearings has to be decreased, which increases thrust bearing dimensions. This effect is caused by excessive thermal deflections of bearing pads, which significantly change oil gap geometry, and in consequence, decreases bearing load-carrying ability. Design of hydrodynamic thrust bearing of large dimensions seems to be a demanding engineering challenge, and additional difficulty comes from limited possibilities of experimental testing of these systems due to high costs. Theoretical investigations, carried out with the use of specially developed computer models, remain a feasible alternative for experimental research. But the accuracy of the models is not often directly validated, because of the lack of appropriate experimental data coming from large objects. In this paper, results of calculations carried out for a large hydrodynamic thrust bearing are shown and compared to measurement data obtained at bearing commissioning stage. Pad temperatures profile sliding surface, oil pressure in hydrodynamic gap and film geometry are compared to the measured values. According to the presented comparisons, some conclusions are drawn with respect to the accuracy of models used to predict large thrust bearing performance.

Centrally Pivoted Tilting Pad Thrust Bearing with Carbon-Based Coated Collar—Experimental Results of Low- and Medium-Speed Operation

Experimental results of the research on a tilting pad thrust bearing with symmetrical pad support in the conditions of high loads and low speeds are presented in the paper. As described in the literature review, experimental results of tilting pad bearings at low speed/high load regime and transient conditions are rare. Unusual material selection - steel pad against a DLC-type coating on the collar was utilized. Such material combination has been mostly used in automotive industry in concentrated contact friction pairs, but it is not commonly used in thick film contacts. The tests included low speed high load and a test, where a Stribeck curve was reproduced. The steel pads showed minimum traces of contact and no visible wear was noticed on the collar coating. Differences of operation in medium and low speed were observed. Big variations of bearing temperature at medium speed and almost constant pad temperature at low speed were measured. At a specific load of 5 MPa transition to mixed friction was occurring at a sliding speed of approx. 0.18 m/s.

On the Possibilities of Decreasing Power Loss in Large Tilting Pad Thrust Bearings

Different systems of direct oil supply have been developed in order to facilitate efficient introduction of fresh lubricant to the oil gap and reduction of churning power loss in tilting pad thrust bearings. Up to now there is no documented application of the supply groove in large thrust bearings used in water power plants. The results of modeling lubricant flow in the lubricating groove of a thrust bearing pad will be presented in the paper. CFD software was used to carry out fluid film calculations. Such analysis makes it possible to modify groove geometry and other parameters and to study their influence on bearing performance. According to the results a remarkable decrease in total power loss due to avoiding churning losses can be observed in the bearing.

Knocking Sounds in the Wind Turbine Gearbox During Slowing Down—Case Study

In the gearbox of a wind turbine under investigation, a knocking sound was noticed during coasting down of the machine. The noise was present in one of several gearboxes of the same type and the search for the source of the sound was undertaken. Gearbox manufacturer specialists after an inspection were pointing out sources outside the gearbox —runner unbalance or generator, but the machine owner ordered an additional research comprising vibration measurement and further analyses. The analysis of the vibration signal was carried out with the use of advanced signal analysis tools and the knocking vibration frequency was found to be the same as the frequency of the intermediate shaft. A machine inspection which was carried out pointed at a few potential sources of the sound, but did not specifically determined its source.

THE INFLUENCE OF HOUSING ARRANGEMENT AND INTERFERENCE ON PRELOAD AND THEORETICAL LIFETIME OF A SYSTEM OF TAPER ROLLER BEARINGS OF A HIGH SPEED SHAFT OF A WIND TURBINE GEARBOX

A system of two taper roller bearings can carry loads with a high ratio of axial load to radial load. Such a system was proposed for a wind turbine gearbox following the poor durability of original bearing design with the aim of increasing durability. Because of size limits, a proposed system is composed of two different taper roller bearings. Standard manufacturers’ catalogues do not provide information on recommended preload or clearance conditions or the durability as a function of pre-load. That was the reason why durability was calculated on the basis of software provided by one of the manufacturers. The analysis presented in the paper shows the relationship between bearing fits, preload values, and the theoretical durability of the bearing. Słowa kluczowe: przekładnia turbiny wiatrowej, łożyska stożkowe, napięcie wstępne, trwałość łożysk. Streszczenie Zastosowanie zespołu łożysk stożkowych napiętych wstępnie pozwala przenosić obciążenia charakteryzujące się wysokim stosunkiem siły osiowej do siły promieniowej. Rozwiązanie wykorzystujące taki układ zaproponowano do przekładni turbiny wiatrowej w celu poprawy trwałości łożyskowania. Ze względu na ograniczenia gabarytowe jak i warunki obciążenia, zaproponowano układ dwóch różnych łożysk stożkowych. Katalogi producentów łożysk nie przedstawiają metod obliczeniowych trwałości takich zespołów. Trwałość zespołu łożyskowego została obliczona z wykorzystaniem oprogramowania dostarczonego przez producenta łożysk zgodnie z normą ISO/TS 16281:2008. W pracy przedstawiono analizę wzajemnych zależności między pasowaniem łożysk oraz wstępnym luzem osiowym między łożyskami układu a roboczym napięciem wstępnym oraz obliczeniową trwałością. 22 ISSN 0208-7774 T R I B O L O G I A 4/2017 Fig. 2. The proposal of modernization of bearing system with utilization of tapered roller bearings (3) Rys. 2. Propozycja modernizacji węzła łożyskowego wykorzystująca zespół łożysk stożkowych (3) Because of space limitations and the requirement of minimizing necessary modifications of other parts of the gearbox, the proposed system utilizes two different roller element bearings. In such a system, specifying an optimum value of operational clearance is crucial, as shown qualitatively in the graphs provided by bearing manufacturers (Fig. 3) (5). SYSTEM SETUP The modelled system was prepared in the BEARINX online Shaft Calculation tool (5). The program was made available to Gdansk University of Technology by the Shaeffler Group for academic purposes. The application performs calculations based on ISO/TS 16281:2008. The method accounts for load distribution between separate rolling elements with the consideration of tilting and misalignment of bearing raceways. The result of calculation contains, inter alia, the values of life rating, load distribution of rolling elements, loads to which the bearings are subjected, equivalent dynamic load, and values of displacements of bearings. The model (Fig. 4) represents the shaft geometry of the high speed shaft of a 1.5 MW wind turbine. The shaft is supported on two sides by bearings. On the left-hand side, there is NU-230 cylindrical roller bearing, and the system of two tapered roller bearings (32230-A, 30230A) are mounted on the right side. Inner raceways of the bearings are set to be located rigidly on the shaft, allowing shaft displacement to be transferred to the roller-raceway connection. The outer raceways of two bearings are set to be connected to the rigid environment, assuming that the gearbox housing ensures support stiffness. One of the tapered roller bearing’s outer raceways is supported with other means, i.e. it is rigidly connected to the additional bushing. The bushing position is restricted with the exception of the axial direction, allowing the creation of the preload by the change of the position of the outer race of the bearing. The displacement is forced by a pressure spring. Fig. 1. Failure rate of 3 MW PL-PL-PA gearbox (1) Rys. 1. Awaryjność przekładni 3 MW PL-PL-PA turbin wiatrowych (1) Fig. 3. Bearing life vs. bearing operating setting (5) Rys. 3. Wpływ napięcia wstępnego na trwałość łożysk (5) Fig. 4. Model of examined system (6) Rys. 4. Model badanego układu (6) During the calculations, the spring preload was a varying input factor, from 0 kN to 25 kN with an increment of 1000 N, and further with a step of 5000 N to 50 kN. Additionally, unstable load conditions, due to changing wind, were considered. On the basis of wind speed data and the power curve for the wind turbine, five working ranges were applied and presented in Table 1. Table 1. Impact of wind speed on wind turbine load (3) Tabela 1. Wpływ prędkości wiatru na obciążenie turbiny (3) Wind speed [m/s] Turbine output Percentage of time [%] Load case 1 over 11 100% 10 Load case 2 1011 75% 11 Load case 3 7-10 50% 29 Load case 4 4-7 25% 32 Load case 5 0-4 0% – turbine stopped 18 23 ISSN 0208-7774 T R I B O L O G I A 4/2017

Special Issue on Sliding Contact Bearings

Continued tendency for machinery to have highenergy density, enhanced precision of motion, and ultra-fast speed of operation poses special challenges for bearing systems. In certain applications, such as nano-positioning, high-speed turbo-machinery, and large water turbines, only sliding contact bearings can meet these challenges. Undoubtedly, there is a need to create a stage for exchanging the latest research and development results and sharing experience in research methodology. This, therefore, is the motivation for this Special Issue of the Journal of Engineering Tribology dedicated to Sliding Contact Bearings. The study of sliding contact bearings started quite a long time ago with pioneering works by Tower, Reynolds, and Petroff, just to mention few most prominent researchers, and was confined, almost exclusively, to hydrodynamic lubrication—a specialist branch of fluid mechanics. Nowadays, sliding contact bearings encompass quite a large area including selflubricating bearings (dry), boundary, and mixed lubricated bearings. Self-levitating air bearings, utilizing near-field acoustic levitation, represent a fairly new development in the area. Also recent advances in large, slow rotating thrust bearings demonstrate that progress is always possible even in the area considered to be mature. The purpose of this Special Issue, to which authors from a number of countries contributed, is to create an opportunity for scientists, engineers, and practitioners to present their latest theoretical and technological advancements in sliding contact bearing engineering and technology. Modern computing/ design techniques and production capabilities help sliding contact bearings regain their position in today’s advanced technology. The Guest Editors of this Special Issue would like to thank the authors for their contributions, the time spent in preparing their manuscripts as well as responding within the deadlines. We hope that this Special Issue will be of interest to readers who are interested in finding out about recent progress in the field of sliding contact bearings.

Large Thrust Bearing Modeling: Influence of Thermal Boundary Conditions and Runner Deformations on Results of TEHD Analysis

In the paper, numerical TEHD results for one of the biggest water power plant Itaipu were compared to available measurement data. Numerical simulations were carried out with the use of bearing model for which the accuracy was previously confirmed with the measurements available for smaller bearings. Several cases were analyzed. The only differences between the cases are the applied boundary conditions. The influence of heat transfer coefficient assumed at bearing pad side walls and collar deformation on predicted bearing performance was determined. Some conclusions concerning large thrust bearing modeling were drawn on the basis of comparisons of the theoretical results to measurements for analyzed bearing system.Copyright