The application of sliding planet gear bearings in wind turbine gearboxes has become more common in recent years. Assuming practically applied helix angles, the gear mesh of the planet stage causes high force and moment loads for these bearings involving high local loads at the bearing edges. Specific operating behavior and suitable design measures to cope with these challenging conditions are studied in detail based on a thermo-hydrodynamic (THD) bearing model. Radial clearance and axial crowning are identified as important design parameters to reduce maximum pressures occurring at the bearing edges. Furthermore, results indicate that a distinct analysis of the gear mesh load distribution is required to characterize bearing operating behavior at part-load. Here, operating conditions as critical as the ones reached at nominal load might occur. Wear phenomena can improve the shape of the gap in the circumferential as well as in axial direction incorporating a significant reduction of local maximum pressures. The complexity of the combination of these aspects and the additionally expected impact of structure deformation gives an insight into the challenges in the design processes of sliding planet gear bearings for wind turbine gearbox applications.
The use of planetary gear stages intends to increase power density in drive trains of rotating machinery. Due to lightweight requirements on this type of machine elements, structures are comparably flexible while mechanical loads are high. This study investigates the impact of structure deformation on sliding planet gear bearings applied in the planetary stages of wind turbine gearboxes with helical gears. It focuses on three main objectives: (i) development of a procedure for the time-efficient thermo-elasto-hydrodynamic (TEHD) analysis of sliding planet gear bearing; (ii) understanding of the specific deformation characteristics of this application; (iii) investigation of the planet gear bearing’s modified operating behavior, caused by the deformation of the sliding surfaces. Generally, results indicate an improvement of predicted operating conditions by consideration of structure deformation in the bearing analysis for this application. Peak load in the bearing decreases because the loaded proportion of the sliding surface increases. Moreover, tendencies of single design measures, determined for rigid geometries, keep valid but exhibit significantly different magnitudes under consideration of structure deformation. Results show that consideration of structure flexibility is essential for sliding planet gear bearing analysis if quantitative assertions on load distributions, wear phenomena, and interaction of the bearing with other components are required.
Summary
With the goal of saving energy and reducing emissions, a secondary-balance technology was used to reform the conventional beam-pumping unit. The output torque from the reduction gearbox of conventional beam-pumping units is usually characterized by its periodic dramatic changes. On the basis of the idea of “cutting peak and filling valley” and the theory of the Fourier-series expansion for the torque curve, the secondary-balance device is designed to slow down the fluctuations in the torque curve. The secondary-balance device, with a balance principle similar to that of the crank balance, is connected to the output shaft of the reduction gearbox and can further reduce torque-fluctuation rate and peak torque. The field-test result of the secondary-balance device shows that the root-mean-square torque is decreased by 22.7%, and the energy-saving rate of the motor reaches 6.54%.
In order to research the chordwise swept cascade stage control mechanism for internal flow field under the off-design condition, the 600 MW supercritical steam turbine HP rotor and static blades were selected as prototypes. The chordwise fore-swept cascade stage and chordwise aft-swept cascade stage were achieved with 30% blade height and 20°, -20° swept angle respectively. The three cascades passage flow numerical simulation was conducted by CFD software. The computed results indicated that the degree of reaction and isentropic efficiency of the three cascade stages were changed very little in the scope of 70~120% design flux and decreased sharply when the inlet flux was less than 50% design flux. On the whole, chordwise fore-swept cascade stage had the best aerodynamic performance.
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