Session: 01-11-01: Wind Energy

Paper Number: 109038

109038 - Tonality Mitigation of Wtg Drivetrains by Applying Advanced Materials to Powertrain Components 

The trend towards a higher degree of integration of drivetrain architectures mainly stems from a cost-driven urge to further increase the power density of wind turbine (WT) drivetrains. A rigid arrangement with the main bearing unit, the gearbox, and the generator, normally does neither feature any elastic elements such as hydraulic-elastomer gearbox mounts, nor an elastic high speed shaft coupling, and will result in unfavorable parasitic forces, because residual non-torque loads will be transferred unfiltered to the gearbox. Reduced decoupling of these components also leads to new questions regarding gearbox input loads and NVH behaviour of these WTs, because sources of vibrations, like gearbox and generator, can no longer be separated regarding loads and structure-borne sound. This leads to inevitable tonalities, which needs to be handled before reaching the sound radiation surfaces of tower and blades.

On top of these challenges with decoupled compact drivetrains, advances in the field of aerodynamic noise, are resulting in reduced masking of drivetrain sounds. Moreover, growing power densities also have an impact on the dynamic behaviour of the system in terms of increasing the ratio of excitation energy versus damping effect of the drivetrain mass. Together with stricter noise codes and the need of erecting wind parks closer to urbanized areas, it is obvious that tonalities of WTs are increasingly coming into focus of the industry.

Tonalities can efficiently be neutralised by systematically decoupling excitations in the drivetrain from the sound emitting surfaces of the wind turbine. A low-speed shaft coupling (LSSC) made of advanced composites has already proven to be an effective way to lower gearbox input loads in WT drivetrains. This paper will answer the question, if LSSCs are additionally a solution for the limitation of structure-borne sound transfer into the sound radiating components of wind turbine structures. For this purpose, a full flexible state of the art WT model was developed in a multibody simulation (MBS) environment. A reference WT model is compared to a WT model equipped with a LSSC between main shaft and gearbox. Transient simulations are performed and a dynamic analysis as well as transfer path analysis (TPA) are carried out on the data.

The second main part of this paper unveils findings on another potential NVH mitigating solution which is addressing the origin of drivetrain sounds, mode shapes in the frequency range up to 250 Hz. One of these is torsional eigenfrequency dominated by the sun shaft of the 2^nd planetary stage of typical 2- or 3-stage wind turbine gearboxes. In most designs, this shaft is forming one of the elements in the drivetrain with the lowest torsional stiffness. As this eigenmode is quite susceptible for gear mesh excitations, its frequency needs to be carefully adjusted to the gear mesh orders and turbine operation range by tuning the respective torsional stiffness of the sun shaft. Usually, the sun shaft diameter as well as length, which determines the stiffness, are determined by the available installation space. Made from steel, the range of tuning the resonance frequency by lowering the torsional stiffness is very limited. Considering a material with a considerably lower Young’s Modulus compared to steel can change this limitation. For many years, carbon fibre driveshafts have been used in other applications like marine, aerospace and automotive. The presentation will show how advanced fiber technology has been transferred from marine propulsion into the wind business and how a semi-torsional elastic coupling can allow to tune the system in such a way to achieve a tonality-free drivetrain.

Presenting Author: Alexander Kari Geislinger GmbH

Presenting Author Biography: Alexander Kari has been working in the wind industry for over 15 years. Currently, his position is Business Development Manager. His main role is to develop wind power to a major market segment within Geislinger. That includes forging links to key contacts within wind turbine and gearbox manufacturers, but also academy, to establish and to thrive the development of powertrain components to enhance wind powertrains. The first wind power product Geislinger introduced has been Compowind®, a novel low-speed shaft coupling based on advanced composite technology. The past few years have been dominated by the development of gearbox integrated solutions to overcome noise, vibration and tonality issues and the successful market introduction. Before joining Geislinger, Alex has been with Miba Bearings for over eight years, thriving the development and introduction of hydrodynamic journal bearings to replace roller element bearings in wind gearboxes, as a basis for a new business segment. He holds a college degree in mechanical engineering as well as a Masters’ Degree in International Business.

Authors:

Alexander Kari Geislinger GmbH
Martin Cardaun Chair for Wind Power Drives
Wilhem Schünemann Center for Wind Power Drives
Ralf Schelenz Center for Wind Power Drives
Christof Sigle Geislinger GmbH