The influence of incoming turbulence on the dynamic modes of an NREL-5MW wind turbine wake

Cillis, Giovanni De; Cherubini, Stefania; Semeraro, Onofrio; Leonardi, Stefano; Palma, P. De

doi:10.1016/j.renene.2021.11.037

Cited by 35 publications

(28 citation statements)

References 36 publications

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“…Here, the first wake is allowed to breakdown to create an unsteady inflow to the second turbine. This is similar to De Cillis et al [14], except that the source of the unsteady inflow in the present study is the upstream turbine wake. De Cillis et al found that atmospheric turbulence drastically altered the dynamics of the wake when compared to the laminar inflow case.…”

Section: Introductionsupporting

confidence: 87%

“…Debnath et al [13] observed that the inclusion of the tower and nacelle in ALM-LES simulations with laminar inflow altered some of the tip vortex breakdown mechanisms identified in the case without supporting structures. De Cillis et al [14] applied DMD to the flow of a wind turbine wake with and without background turbulence and concluded that in the turbulent case, the exogenous background flow dynamics prevail compared to the endogenous higher frequency dynamics of the wake. Additionally to the diagnostics, the modes can also be used to build reduced order models for the temporal prediction of the flow by either projection in the case of POD [15], or by directly using the known mode frequencies in the case of DMD [16].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Dynamic Mode Decomposition of merging wind turbine wakes

Zormpa,

Le Clainche,

Ferrer

et al. 2023

J. Phys.: Conf. Ser.

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The design and operation of wind farms is significantly affected by the impact that upstream turbine wakes have on the power production and fatigue loading of subsequent turbines; often called the wake effect. In this work, two types of flows are considered: the wake of a single turbine with a laminar inflow and the combined wake of two turbines operating in-line where the upstream wake results in an unsteady inflow for the downstream turbine. Those two scenarios are simulated using large eddy simulation (LES) and the actuator line method (ALM). The spatio-temporal velocity fields are analyzed by means of high order dynamic mode decomposition (HODMD), a well established variant of the DMD. The results show that most of the higher frequencies characterizing the laminar case are instead dominated by the lower frequency modes in the combined wake. This suggests that structures emerging from the blade rotations in a wind turbine wake may be less significant for describing the wake dynamics when the rotor is operating in the unsteady wake of an upstream rotor.

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Section: Introductionsupporting

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Dynamic Mode Decomposition of merging wind turbine wakes

Zormpa,

Le Clainche,

Ferrer

et al. 2023

J. Phys.: Conf. Ser.

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“…As shown in detail in Ref. [23], the time-and spaceaveraged streamwise velocity profiles are well fitted with a logarithmic law in the inner region, starting from the region on top of the roughness elements, while the profile in the outer region is well described by a power law having shear coefficient α = 0.27. The turbulence intensity is approximately 10% at the hub height.…”

Section: Simulation Setupmentioning

confidence: 54%

“…However, as recently shown in Ref. [23] by means of dynamic mode decomposition, these highly energetic vortical structures loose their dynamical relevance when the turbine is impinged by a turbulent inflow. This suggests that the entrainment of the outer flow as well as the wake recovery, might be considerably affected as well.…”

Section: Introductionmentioning

confidence: 58%

How incoming turbulence affects wake recovery of an NREL-5MW wind turbine

Cherubini

Cillis²,

Semeraro

et al. 2022

J. Phys.: Conf. Ser.

Self Cite

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The present work aims at investigating the effect of inflow turbulence on the wake recovery of the NREL-5MW reference wind turbine. The wake produced by a utility-scale wind turbine invested by both a laminar uniform inflow and a turbulent flow, is analyzed by means of proper-orthogonal decomposition (POD). The considered turbine is the NREL-5MW at tip-speed ratio λ = 7 and a diameter-based Reynolds number of the order 108. The flow is simulated through Large Eddy Simulation, where the forces exerted by the blades are modeled using the Actuator Line Method, whereas tower and nacelle are modeled employing the immersed boundary method. The main flow structures identified by modal decomposition in both of the considered cases are compared, and some differences emerge, which can be of great importance for the formulation of a reduced-order model. Among the most energetic modes, a high-frequency mode directly related to the tip vortices is found only in the flow case with laminar inflow. In the presence of inflow turbulence, the most energetic modes are all composed by large-scale low-frequency structures filling the whole domain. We evaluate the contribution of each POD mode to wake recovery reconstructing the total flux of mean kinetic energy due to turbulent fluctuations on a closed surface enclosing the wake of the wind turbine. In the laminar-inflow case, we have found that the POD modes related to the tip and root vortices do not contribute positively to the wake recovery, but they rather sustains the velocity gradient, as already established by Lignarolo et al. (2015) for a wind-turbine model. Whereas, in the turbulent-inflow case, all the most energetic modes contribute positively to wake recovery. These results clearly indicate that inflow turbulence should be taken into account for accurately estimate the entrainment process in the wake of wind turbines. NREL 5MW wind turbine, POD, laminar or turbulent inflow, wake recovery, turbulent kinetic energy entrainment.

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“…High turbulence level has been shown to accelerate the disintegration of coherent vortex rings in the simulations of Yılmaz and Meyers 45 . Also, for a fixed-bottom wind turbine with turbulent inflow, De Cillis et al 47 observed that the modes due to tip vortex instabilities are superseded by modes related to flow fluctuations coming from incoming turbulence. Nevertheless, the motion of floating turbines imposes very specific perturbations, that are not present on fixed-bottom turbines.…”

Section: B Comparison To the Stability Theorymentioning

confidence: 99%

The Stability of Wakes of Floating Wind Turbines

Kleine,

Franceschini,

Carmo

et al. 2022

Preprint

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Floating offshore wind turbines (FOWTs) are subjected to platform motion induced by wind and wave loads. The oscillatory movement trigger vortex instabilities, modifying the wake structure, influencing the flow reaching downstream wind turbines. In this work, the wake of a FOWT is analysed by means of numerical simulations and comparison with linear stability theory. Two simplified models based on the stability of vortices are developed for all degrees of freedom of turbine motion. In our numerical simulations, the wind turbine blades are modeled as actuator lines and a spectral-element method with low dispersion and dissipation is employed to study the evolution of the perturbations. The turbine motion excites vortex instability modes predicted by the linear stability of helical vortices. The flow structures that are formed in the non-linear regime are a consequence of the growth of these modes and preserve some of the characteristics that can be explained and predicted by the linear theory. The number of vortices that interact and the growth rate of disturbances are well predicted by a simple stability model of a two-dimensional row of vortices. For all types of motion, the highest growth rate is observed when the frequency of motion is one and a half the frequency of rotation of the turbine; that induces the out-of-phase vortex pairing mechanism. For lower frequencies of motion, several vortices coalesce to form large flow structures, which cause high amplitude of oscillations in the streamwise velocities, that may increase fatigue or induce high amplitude motion on downstream turbines.

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The influence of incoming turbulence on the dynamic modes of an NREL-5MW wind turbine wake

Cited by 35 publications

References 36 publications

Dynamic Mode Decomposition of merging wind turbine wakes

Dynamic Mode Decomposition of merging wind turbine wakes

How incoming turbulence affects wake recovery of an NREL-5MW wind turbine

The Stability of Wakes of Floating Wind Turbines

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