Stephan Neumann

CFD simulation of elastohydrodynamic lubrication problems with reduced order models for fluid-structure interaction

Abstract Recently, simulations of elastohydrodynamic lubrication (EHL) problems based on a coupled solution of the Navier–Stokes equations and solid mechanics have been presented. Compared to classical approaches in EHL, however, the simulation time is significantly higher. In this work, the elastic solids are represented by reduced finite element (FE) models in order to decrease the calculation time while keeping the possibility to simulate complex geometries and materials. To eliminate the necessity of matching meshes at the fluid–solid interface, an interpolation method based on radial basis functions is applied to an EHL line contact. By using this energy-conserving interpolation, the number of solid interface points is reduced by a factor of four compared to the fluid interface points with approximately identical pressure and film thickness profiles. Hence, the memory size of the FE matrices can be reduced by more than 90%, leading to an efficient deformation calculation even for complex solids.

Robustness Test for Wind Turbine Gearbox Bearings

This paper introduces an innovative approach for the creation of the robustness test against specific failures of the planetary and HSS bearings (e.g. classical fatigue, smearing, micro-pitting, and lip fractures) in the wind turbine gearboxes. The introduced Bearing Robustness Test (BRT) considers the system-dependent characteristics (e.g. drive train design, interaction between components, assembly process, lubricant aging) and real dynamic load conditions, frequencies and sequence. The creation of the BRT is based on field and simulation data. The core element is the simulative approach for the determination of the relation between external wind and grid loads on the one side and local loads of the bearing on the other side. BRT aims the mapping of the most critical, but real, field load situations in the bearing test rig. By means of the BRT it is possible to evaluate the robustness of bearing against specific field conditions in the early stage of the product cycle and consequently to enhance the quality and to reduce the failure rate of the bearing. 1. Motivation and Objectives The cost-efficiency of the wind turbines is reduced by the frequent failures of the main gearboxes. The main gearbox is responsible for nearly 60 % of the downtime of the wind turbine, see Figure 1. This fact is caused by a fluctuating and dynamic wind and grid loads, dynamic interaction between drive train components as well as the demand for high power density of the gearbox components [1]. Therefore, the rolling contact bearings are the most critical component of the main gearbox. They contribute to over 67 % of main gearbox failures according to the current research, see Figure 1. The planetary and high-speed shaft (HSS) bearings failures cause high reparation, replacement and service costs [3]. Bearing testing methods within the product development process could contribute to more reliable and robust gearbox bearings and thereby increase the availability of the wind turbines. Nowadays, the existing testing methods cannot completely simulate the real elastic surroundings and reproduce the complex load situation on the bearing as well as the complex interaction between the gearbox components. Consequently, it is difficult to reproduce specific wind turbine bearing failures in a realistic way [4]. To solve this challenge, a diversified consortium of a complete product value chain (bearing, gearbox and wind turbine manufacturer)1 under the lead management of Chair for Wind Power Drives (CWD) got together to develop a new bearing test rig designs (a planetary 1 Schaeffler, SKF, Timken, NTN, Siemens Winergy, ZF Wind Power, Eickhoff, Vestas, Nordex, Senvion Figure 1. Causes for wind turbine downtime. 3% 3% 8% 2% 25%

A Sensitivity analysis of planetary- and high speed shaft bearing loads in wind turbines

Long downtime periods burden the economic efficiency of wind turbines (WT). 60% of all downtime periods are caused by gearbox failures and most of them are caused by bearing outages [1]. Planetary and high speed shaft bearing failures are responsible for more than 70% of these bearing outages [2]. The causes for these failures are frequently dynamical mechanical loads at the bearing stages. This shows that the dynamic loads at these bearing stages are yet not sufficiently well known. To analyse the influences on bearing loads at the planetary and high speed shaft stage, a sensitivity analysis with varying loads at the hubflange for pitch-, yaw-, drive-torque and thrust is done. As additional factors different bearing clearances and shaft stiffnesses were considered. The results show, that the drive torque at the hub flange has the main influence on value, amplitude and

Reduzierung von Lagerschäden im Antriebsstrang von Windenergieanlagen : WEA-Lagerzentrum.NRW

In dem von der Europäischen Union und dem Land Nordrhein-Westfalen geförderten Projekt WEA-Lagerzentrum.NRW forschen Wissenschaftler des Center for Wind Power Drives (CWD) der RWTH Aachen gemeinsam mit dem „Who ́s Who“ der Windenergieanlagenbranche und wichtigen Zulieferern an der Entwicklung neuartiger Tests zur Qualifizierung von Lagern für Windenergieanlagen (WEA). Im Rahmen des Projektes werden dazu zwei neuartige und weltweit einzigartige Prototypenprüfstände zur Untersuchung realgroßer WEA-Getriebelager aufgebaut sowie neuartige Testprozeduren zur Freigabe von Lagern entwickelt und deren Wirksamkeit nachgewiesen.