Exploring the capabilities of active grids

Neuhaus, Lars; Berger, Frederik; Peinke, Joachim; Hölling, Michael

doi:10.1007/s00348-021-03224-5

Cited by 31 publications

(17 citation statements)

References 23 publications

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“…Correlation coefficients within the local stream-tube radius are very high for both wind fields and for the sine variation for all measured positions, as expected based on the investigation by Neuhaus et al (2021). For the stochastic variation the correlation decreases towards the edge of the active grid inner square, with still high values within R ef f .…”

Section: Wind Fieldssupporting

confidence: 84%

Experimental analysis of the dynamic inflow effect due to coherent gusts

Berger¹,

Neuhaus²,

Onnen³

et al. 2022

Preprint

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Abstract. The dynamic inflow effect describes the unsteady aerodynamic response to fast changes in rotor loading, due to the inertia of the wake. For pitch actuation and fast rotor speed changes this effect leads to load overshoots. The effect is suspected to be also relevant for gust situations, however this was never shown. The objective of the paper is to proove the dynamic inflow effect due to gusts and compare dynamic inflow engineering models to corresponding measurements. A 1.8 m diameter model turbine is used in the large wind tunnel of ForWind – University of Oldenburg with an active grid to impress rotor uniform gusts on the flow. The campaign features load and velocity measurements of the axial flow in the rotor plane. The unsteady dynamic inflow effect is investigated by comparing two experimental cases. Firstly, a dynamic measurement during a gust situation is performed. Secondly, quasi-steady loads and axial velocities are interpolated from a steady characterisation experiment according to the gust wind speed. By comparing both cases, the influence attributed to the dynamic inflow effect is isolated. Further comparisons to a typical Blade Element Momentum code and a higher fidelity Free VortexWake Model are performed. Based on analytical considerations an improvemed formulation of the Øye dynamic inflow model is proposed. The experiment shows a dynamic inflow effect due to gusts in the loads and axial velocity measurements. It leads to a reduction in load and axial velocity amplitudes and consequently also lower fatigue loading. The higher fidelity model shows a similar impact of the dynamic inflow effect. In contrast, the commonly used Øye engineering model in the BEM code predicts an increase in load amplitude and thus higher fatigue loads. The improved Øye engineering model however catches the observed dynamic inflow effect due to gusts in accordance to the experiment and FVWM simulations. An amplification of induced velocities, seen in the experiment and FVWM simulation, causes the reduced load amplitudes. Therefore, classic dynamic inflow models, which filter the induced velocity, cannot predict the effect. The proposed improvement to additionally consider the wake velocity for the filter of the dynamic inflow engineering model, proves to be a straight forward but also effective modification. In conclusion, these new experimental findings on dynamic inflow due to gusts and improvements to the Øye model enable improvements in wind turbine design by catching the related lower fatigue loads.

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Section: Wind Fieldssupporting

confidence: 84%

Experimental analysis of the dynamic inflow effect due to coherent gusts

Berger¹,

Neuhaus²,

Onnen³

et al. 2022

Preprint

Self Cite

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“…Movement on each shaft is induced individually through digitally controlled servomotors. More information can be found in [10,11].…”

Section: Deployment and Measurementsmentioning

confidence: 99%

“…The characterised wind patterns are a sinusoidal gust with 2 Hz frequency and a 4 Hz mexican hat one. The inflows are assumed to be coherent on the rotor area [11]. (ii) The probe is moved out and the wind tunnel runs.…”

Section: Measurement Proceduresmentioning

confidence: 99%

Design and evaluation of rotor blades for fluid structure interaction studies in wind tunnel conditions

Langidis

Nietiedt

Berger

et al. 2022

J. Phys.: Conf. Ser.

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Wind tunnel experiments with wind turbine models are a promising method for investigating fluid structure interaction (FSI) phenomena. However, the lack of suitable models that feature properly scaled blades and the complexity of aeroelastic and fluid dynamic measurements during turbine operation is challenging. In this paper, the design methodology for aeroelastically scaled blades which are intended for Model Wind Turbine Oldenburg (MoWiTO) 1.8 is presented. The scaling relations are formulated, initiating from the existing turbines’ design. Next, the manufactured blades are equipped on MoWiTO and are subsequently evaluated, during operation under gusty wind fields produced by an active grid. The tip deflection is recorded using an innovative photogrammetry setup. Simulations of an OpenFAST model, which has properties extracted from the scaling formulation, are used as reference. The recorded loads and blade deformations show similar dynamics, compared to the reference. These results prove the design successful, and the capability of measuring FSI phenomena in wind tunnel environment is showcased.

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“…An active grid is attached to the wind tunnel nozzle to manipulate the flow (Kröger et al, 2018;Neuhaus et al, 2021). The grid consists of 80 individually controllable shafts with rectangular flaps to control the distribution of blockage of the flow.…”

Section: Active Gridmentioning

confidence: 99%

Experimental analysis of the dynamic inflow effect due to coherent gusts

et al. 2022

Self Cite

View full text Add to dashboard Cite

Abstract. The dynamic inflow effect describes the unsteady aerodynamic response to fast changes in rotor loading due to the inertia of the wake. Fast changes in turbine loading due to pitch actuation or rotor speed transients lead to load overshoots. The phenomenon is suspected to be also relevant for gust situations; however, this was never shown, and thus the actual load response is also unknown. The paper's objectives are to prove and explain the dynamic inflow effect due to gusts, and compare and subsequently improve a typical dynamic inflow engineering model to the measurements. An active grid is used to impress a 1.8 m diameter model turbine with rotor uniform gusts of the wind tunnel flow. The influence attributed to the dynamic inflow effect is isolated from the comparison of two experimental cases. Firstly, dynamic measurements of loads and radially resolved axial velocities in the rotor plane during a gust situation are performed. Secondly, corresponding quantities are linearly interpolated for the gust wind speed from lookup tables with steady operational points. Furthermore, simulations with a typical blade element momentum code and a higher-fidelity free-vortex wake model are performed. Both the experiment and higher-fidelity model show a dynamic inflow effect due to gusts in the loads and axial velocities. An amplification of induced velocities causes reduced load amplitudes. Consequently, fatigue loading would be lower. This amplification originates from wake inertia. It is influenced by the coherent gust pushed through the rotor like a turbulent box. The wake is superimposed on that coherent gust box, and thus the inertia of the wake and consequently also the flow in the rotor plane is affected. Contemporary dynamic inflow models inherently assume a constant wind velocity. They filter the induced velocity and thus cannot predict the observed amplification of the induced velocity. The commonly used Øye engineering model predicts increased gust load amplitudes and thus higher fatigue loads. With an extra filter term on the quasi-steady wind velocity, the qualitative behaviour observed experimentally and numerically can be caught. In conclusion, these new experimental findings on dynamic inflow due to gusts and improvements to the Øye model enable improvements in wind turbine design by less conservative fatigue loads.

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Exploring the capabilities of active grids

Cited by 31 publications

References 23 publications

Experimental analysis of the dynamic inflow effect due to coherent gusts

Experimental analysis of the dynamic inflow effect due to coherent gusts

Design and evaluation of rotor blades for fluid structure interaction studies in wind tunnel conditions

Experimental analysis of the dynamic inflow effect due to coherent gusts

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