Friction as a major uncertainty factor on torque measurement in wind turbine test benches

Abstract

Most of the existing multi-MW nacelle test benches (NTB) measure the MN•m torque before load application system (LAS) to reduce the cross-talk effect of the multi-component forces and bending moments on torque measurement. This means that the friction torque of the LAS reduces the applied torque and consequently directly determines the input torque on the device under test (DUT). Therefore, the knowledge of the friction torque is necessary for the precise experimental investigations (e.g. efficiency measurement). At the beginning of this paper, a Computational Fluid Dynamics (CFD) simulation method for the determination of the friction torque of the LAS, which is suspended by hydrostatical plain bearings, is introduced. Subsequently, this method is validated with experimental results. Afterwards the friction torque of the LAS is quantified under different operation conditions (e.g. variation of rotational speed, multi-component load and temperature). Finally, the influence of the quantified friction torque on the uncertainty of the MN•m measurement is compiled.