Actuator Line Method Simulations for the Analysis of Wind Turbine Wakes Acting on Helicopters

Bühler, Manuel N.; Weihing, Pascal; Klein, Levin; Lutz, Thorsten; Krämer, Ewald

doi:10.1088/1742-6596/1037/6/062004

Cited by 9 publications

(10 citation statements)

References 8 publications

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“…The ALM is based on a blade‐element approach in which body forces are introduced in the Navier‐Stokes equations along lines representing the blades of the wind turbine. It was originally developed for simulating the wake behind a single horizontal axis wind turbine, and has later been extended to simulate flows in wind farms, and applied to vertical axis wind turbines, tidal turbines, and helicopters . For a review of the ALM and related methods, the reader is referred to Breton et al In the ALM, the body forces are obtained from tabulated airfoil data employing the local angle of attack along the blades as input.…”

Section: Introductionmentioning

confidence: 99%

A new tip correction for actuator line computations

Dag

Sørensen

2019

Wind Energy

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The actuator line method (ALM) is today widely used to represent wind turbine loadings in computational fluid dynamics (CFD). As opposed to resolving the whole blade geometry, the methodology does not require geometry-fitted meshes, which makes it fast to apply. In ALM, tabulated airfoil data are used to determine the local blade loadings, which subsequently are projected to the CFD grid using a Gaussian smearing function. To achieve accurate blade loadings at the tip regions of the blades, the width of the projection function needs to be narrower than the local chord lengths, requiring CFD grids that are much finer than what is actually needed in order to resolve the energy containing turbulent structures of the atmospheric boundary layer (ABL). On the other hand, employing large widths of the projection function may result in too large tip loadings. Therefore, the number of grid points required to resolve the blade and the width of the projection function have to be restricted to certain minimum values if unphysical corrections are to be avoided. In this paper, we investigate the cause of the overestimated tip loadings when using coarse CFD grids and, based on this, introduce a simple and physical consistent correction technique to rectify the problem. To validate the new correction, it is first applied on a planar wing where results are compared with the lifting-line technique. Next, the NREL 5-MW and Phase VI turbines are employed to test the correction on rotors. Here, the resulting blade loadings are compared with results from the blade-element momentum (BEM) method. In both cases, it is found that the new correction greatly improves the results for both normal and tangential loads and that it is possible to obtain accurate results even when using a very coarse blade resolution. KEYWORDSactuator line, LES of wind turbines, tip correction, wind turbine blade loadings INTRODUCTIONThe actuator line method (ALM) was developed as a numerical technique to facilitate the representation of the rotor blades in computational fluid dynamics (CFD) simulations of wind turbines. 1 The ALM is based on a blade-element approach in which body forces are introduced in the Navier-Stokes equations along lines representing the blades of the wind turbine. It was originally developed for simulating the wake behind a single horizontal axis wind turbine, 1-4 and has later been extended to simulate flows in wind farms, 5-12 and applied to vertical axis wind turbines, 13,14 tidal turbines, 15-17 and helicopters. 18 For a review of the ALM and related methods, the reader is referred to Breton et al. 19 In the ALM, the body forces are obtained from tabulated airfoil data employing the local angle of attack along the blades as input. The local angle of attack is defined from the local relative velocity, which is determined at each time step while running a simulation. After having determined the local forces, they are projected from the lines representing the rotor blades to the CFD grid points. A main issue of the technique is that it ...

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Section: Introductionmentioning

confidence: 99%

A new tip correction for actuator line computations

Dag

Sørensen

2019

Wind Energy

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“…Ninety-nine actuator line elements were introduced along the blade, with a higher density at the blade tip and root region. The same polar data were used as in [2] and were generated with Xfoil. The size of the ACL regularization kernel was set proportionally to the local airfoil chord length c WT , = 0.25 c WT , according to [30].…”

Section: Cfd Setupmentioning

confidence: 99%

“…Therefore, the HeliOW project (helicopter offshore wind) has been established to assess the suitability of the German regulations to protecting helicopters form potential safety risks. It is a collaborative national research project which includes in situ measurements of WT wakes with unmanned aircraft systems (University of Tübingen [1]), high-fidelity computational fluid dynamic (CFD) simulations of WT wakes (University of Stuttgart [2][3][4][5]), desktop helicopter simulations with mutual interaction between WT wake and helicopter (Technical University of Munich [6,7]) and piloted helicopter simulations in a research flight simulator with a superposition method (DLR [8]).…”

Section: Introductionmentioning

confidence: 99%

Piloted Simulation of the Rotorcraft Wind Turbine Wake Interaction during Hover and Transit Flights

et al. 2022

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Helicopters are used for offshore wind farms for maintenance and support flights. The number of helicopter operations is increasing with the expansion of offshore wind energy, which stresses the point that the current German regulations have not yet been validated through scientific analysis. A collaborative research project between DLR, the Technical University of Munich, the University of Stuttgart and the University of Tübingen has been conducted to examine the sizes of the flight corridors on offshore wind farms and the lateral safety clearance for helicopter hoist operations at offshore wind turbines. This paper details the results of piloted helicopter simulations in a realistic offshore wind farm scenario. The far-wake of rotating wind turbines and the near-wake of non-rotating wind turbines have been simulated with high-fidelity computational fluid dynamics under realistic turbulent inflow conditions. The resulting flow fields have been processed by superposition during piloted simulations in the research flight simulator AVES to examine the flight corridors in transit flights and the lateral safety clearance in hovering flights. The results suggest a sufficient size for the flight corridor and sufficient lateral safety clearance at the offshore wind turbines in the considered scenarios.

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“…In particular, it has been employed in studying the generation and convection of rotor wakes [2,3]. There are also publications where it has been used in helicopter rotor aerodynamic analyses [4][5][6], particularly when costly simulations are involved, in which a detailed distribution of the blade loading is not an absolute requirement. The broad application of AL stems from the high fidelity level that the CFD context provides, alongside with the limited computational requirements of the methodology.…”

Section: Introductionmentioning

confidence: 99%

Investigating the Level of Fidelity of an Actuator Line Model in Predicting Loads and Deflections of Rotating Blades under Uniform Free-Stream Flow

et al. 2021

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In this paper, the accuracy of an in-house Actuator Line (AL) model is tested on aeroelastic simulations of a Wind Turbine (WT) rotor and a helicopter Main Rotor (MR) under uniform free-stream flow. For the scope of aeroelastic analyses, the AL model is coupled with an in-house multibody dynamics code in which the blades are modeled as beams. The advantage from the introduction of CFD analysis in rotorcraft aeroelasticity is related to its capability to account in detail for the interaction of the rotor wake with the boundary layer developed on the surrounding bodies. This has proven to be of great importance in order to accurately estimate the aerodynamic forces and thus the corresponding structural loads and deflections of the blades. In wind turbine applications, a good example of the above is the rotor/ground interaction. In helicopter configurations, the interaction of MR with the ground or the fuselage and the interaction of tail rotor with the duct in fenestron configurations are typical examples. Furthermore, CFD aerodynamic analysis is an obvious modeling option in which the above mentioned asset can be combined with the consideration of the mutual interaction of the rotor with the ambient turbulence. A WT rotor operating inside the atmospheric boundary layer under turbulent free-stream flow is such a case. In the paper, AL results are compared against Blade Element Momentum (BEM) and Lifting Line (LL) model results in the case of the WT, whereas LL and measured data are considered in the helicopter cases. Blade loads and deflections are mainly compared as azimuthal variations. In the helicopter MR cases, where comparison is made against experimental data, harmonic analysis of structural loads is shown as well. Overall, AL proves to be as reliable as LL in the canonical cases addressed in this paper in terms of loads and deflections predictions. Therefore, it can be trusted in more complex flow conditions where viscous effects are pronounced.

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Actuator Line Method Simulations for the Analysis of Wind Turbine Wakes Acting on Helicopters

Cited by 9 publications

References 8 publications

A new tip correction for actuator line computations

A new tip correction for actuator line computations

Piloted Simulation of the Rotorcraft Wind Turbine Wake Interaction during Hover and Transit Flights

Investigating the Level of Fidelity of an Actuator Line Model in Predicting Loads and Deflections of Rotating Blades under Uniform Free-Stream Flow

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