Generation of user defined turbulent inflow conditions by an active grid for validation experiments

Abstract

Abstract. A wind tunnel experiment is presented which combines the use of controlled turbulent inflow conditions and a two-bladed model wind turbine utilizing a new control strategy called subspace predictive repetitive control (SPRC). The validation of the performance of SPRC was made under turbulent inflow conditions generated by an active grid. The 3m × 3m active grid is used in this experiment using a unique method to generate reproducible atmosphericlike turbulent wind fields to act on a medium sized model wind turbine. This contribution is focussing on the detailed description of the experiment and its components and the analysis of the turbulent inflow by means of one and two point statistics. Exemplarily the impact of the new control strategy to the generated turbulent test cases are discussed. IntroductionBecause of the increasing energy consumption and the expansion of renewable energy the demands on wind energy converters are constantly increasing. Especially the development of new offshore wind turbines with higher energy production are of very high importance. As part of the Innwind.eu project, which had the overall objectives of the high performance innovative design of a beyond-state-of-the-art 10-20 MW offshore wind turbine and hardware demonstrators of some of the critical components, new mechanisms for active and passive rotor load control were developed. As the wind fields of the atmospheric boundary layer (ABL) acting on the rotor and the turbine are turbulent as shown in [1], the validation of these new concepts have to take place under controlled turbulent conditions. We present a wind tunnel experiment, which combines a model wind turbine equipped with these new control designs and a turbulent inflow generated by an so called active grid. The active grid is an instrument allowing us to generate turbulence with a wide range of different behaviour, additionally such turbulent flows can be repeated quite accurately. So it is possible to validate these new concepts using different turbulent inflow conditions.

Distinct Turbulent Regions in the Wake of a Wind Turbine and Their Inflow-Dependent Locations: The Creation of a Wake Map

“…The experiments were carried out in Oldenburg's Large Wind Tunnel (OLWiT), a closed-loop wind tunnel that has an inlet of (3 × 3) m 2 and a closed test section of 30 m length (cf. [28]). Wind velocities of up to 42 ms −1 can be achieved, and the background turbulence intensity is 0.3%.…”

Exploring the capabilities of active grids

“…Many new experiments were initiated, which are summarized in a recent review by Mydlarski (2017). Alternating the excitation methods, grids are used (a) to generate homogeneous and isotropic turbulence (HIT) (see Mydlarski andWarhaft 1996, 1998;Shen and Warhaft 2000;Poorte and Biesheuvel 2002;Larssen and Devenport 2011;Hearst and Lavoie 2015;Griffin et al 2019;Cekli et al 2015), (b) to create a defined shear flow in the wind tunnel (see Cekli and van de Water 2010;Hearst and Ganapathisubramani 2017), and (c) to reproduce atmospheric wind conditions either directly (see Reinke et al 2017;Kröger et al 2018a) or by their statistical properties (see Knebel et al 2011;Good and Warhaft 2011;Neuhaus et al 2020).…”

How realistic are the wakes of scaled wind turbine models?

“…The present experimental setup can be further improved, for an even increased realism and expanded capabilities. Regarding the inflow, several facilities have been recently designed or upgraded to generate unstable boundary layers (Chamorro and Porté-Agel, 2010), tornadoes and downbursts (WindEEE, 2020), or for the active generation of turbulent flows (Kröger et al, 2018). Regarding the models, a more realistic geometry and size of the nacelle and tower can be achieved at the price of a further miniaturization.…”