Effects of Support Structures in an LES Actuator Line Model of a Tidal Turbine with Contra-rotating Rotors

Creech, Angus; Borthwick, Alistair G. L.; Ingram, David

doi:10.20944/preprints201703.0230.v1

Cited by 10 publications

(8 citation statements)

References 49 publications

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“…The correction is meant to be applied at the angle of attack calculation stage, where the total additional induction from the wake system, w corr , is added to the local relative velocity and the angle Illustration of a vortex system of a translating planar wing of attack value is determined. To apply the correction, the location of the wake vortices and their strengths have to be defined in advance as these are required, see Equation (16). For a translating planar wing application, wake vortices can be assumed to form a straight vortex sheet which is parallel to the flow and which trail from the quarter-chord line of the wing (see Figure 6).…”

Section: Translating Planar Wingmentioning

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: Translating Planar Wingmentioning

confidence: 99%

A new tip correction for actuator line computations

Dag

Sørensen

2019

Wind Energy

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“…The first approach applies a uniform force to the flow, and it is a computationally inexpensive alternative that allows multiple devices simultaneously, but lose the representation of important elements like rotor swirl [14,15,16]. The latter ALMs and models that consider the detailed geometry of the device improve the turbine representation, but require considerably more computational resources, due to computationally expensive interpolations to the grid nodes and therefore have not been used for large turbine arrays, even though they can resolve near-field features and unsteady vortical structures generated by the turbine geometry [17,18,19,20,21,22,23].…”

Section: Take Down Policymentioning

confidence: 99%

“…To capture dynamically-rich turbulent coherent structures in the wakes, more advanced but expensive models based on large-eddy simulations (LES) can provide accurate descriptions of these flow fields, yielding detailed solutions by resolving directly all the turbulent scales larger than the size of the computational grid. This produces information on the flow unsteadiness, turbulence, and vortical structures, and therefore it has been used to study tidal turbines, but limited to few devices due to its larger computational cost [16,17,18,19,22,23].…”

Section: Take Down Policymentioning

confidence: 99%

“…Taking into account the variety of options to study tidal turbine flows numerically, it is important to consider that the tidal energy sector requires efficient and optimized models that are able to study multiple devices simultaneously, with practical use of computational resources [3,28]. Moreover, it has been demonstrated that turbulence and large-scale structures dominate the performance of tidal turbines, the evolution of their wakes, and their interaction and effects with the flow in the sites where they are installed [10,17,22,23]. Therefore there is a need for efficient methodologies that can provide both the ability to study multiple devices at the same time, while also reporting information on the unsteadiness of the turbulent flows.…”

Section: Take Down Policymentioning

confidence: 99%

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Capturing the development and interactions of wakes in tidal turbine arrays using a coupled BEM-DES model

2019

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“…Combining TPMs with mesh-optimization techniques was first considered by Creech et al, 9 and more recent implementations can also be found in Abolghasemi et al, 10 and Creech et al 11 each employing a different TPM (actuator volume and actuator disk and actuator line based, respectively).…”

mentioning

confidence: 99%

Mesh‐adaptive simulations of horizontal‐axis turbine arrays using the actuator line method

Deskos

Piggott

2018

Wind Energy

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Numerical models of the flow and wakes due to turbines operating within a real‐scale offshore wind farm can lead to a prohibitively large computational cost, particularly when considering blade‐resolved simulations. With the introduction of turbine parametrizations such as the actuator disk (AD) or the actuator line (AL) models, this problem has been partially addressed, yet the computational cost associated with these simulations remains high. In this work, we present an implementation and validation of an AL model within the mesh‐adaptive three‐dimensional fluid dynamics solver, Fluidity, under a unsteady Reynolds‐averaged Navier‐Stokes–based turbulence modelling approach. A key feature of this implementation is the use of mesh optimization techniques, which allow for the automatic refinement or coarsening of the mesh locally according to the resolution needed by the fluid flow solver. The model is first validated against experimental data from wind tunnel tests. Finally, we demonstrate the benefits of mesh‐adaptivity by considering flow past the Lillgrund offshore wind farm.

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Effects of Support Structures in an LES Actuator Line Model of a Tidal Turbine with Contra-rotating Rotors

Cited by 10 publications

References 49 publications

A new tip correction for actuator line computations

A new tip correction for actuator line computations

Capturing the development and interactions of wakes in tidal turbine arrays using a coupled BEM-DES model

Mesh‐adaptive simulations of horizontal‐axis turbine arrays using the actuator line method

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