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:10.3390/en10050726

Cited by 25 publications

(20 citation statements)

References 57 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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“…This paper describes a numerical model of a cross-flow turbine, with the future goal of modellin se-packed tidal rotors comprising many blades. The present model is built upon a previous turbin del, which scales to thousands of cores on a supercomputer [54,56]. Although the present focus a single rotor, the numerical model can be applied to a large-scale turbine farm in future studie e to a lack of experimental data concerning this type of rotor, the numerical model is first validate ainst experimental measurements from a two-bladed H-type wind turbine, and then used t edict turbine loading and investigate vorticity distribution in the vicinity of the rotor.…”

Section: Introductionmentioning

confidence: 99%

“…A newly developed, efficient, parallelised, numerical model of vertical-axis turbines, with a fixe -speed ratio system and with a torque-controlled system, is presented in the following section is computationally efficient numerical model is coupled with and is developed within th This paper describes a numerical model of a cross-flow turbine, with the future goal of modelling close-packed tidal rotors comprising many blades. The present model is built upon a previous turbine model, which scales to thousands of cores on a supercomputer [54,56]. Although the present focus is on a single rotor, the numerical model can be applied to a large-scale turbine farm in future studies.…”

Section: Introductionmentioning

confidence: 99%

Aerodynamic Analysis of a Two-Bladed Vertical-Axis Wind Turbine Using a Coupled Unsteady RANS and Actuator Line Model

et al. 2020

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Close-packed contra-rotating vertical-axis turbines have potential advantages in wind and hydrokinetic power generation. This paper describes the development of a numerical model of a vertical axis turbine with a torque-controlled system using an actuator line model (ALM). The developed model, coupled with the open-source OpenFOAM computational fluid dynamics (CFD) code, is used to examine the characteristics of turbulent flow behind a single two-bladed vertical-axis turbine (VAT). The flow field containing the turbine is simulated by solving the unsteady Reynolds-averaged Navier-Stokes (URANS) equations with a k - ω shear stress transport (SST) turbulence model. The numerical model is validated against experimental measurements from a two-bladed H-type wind turbine. Turbine loading is predicted, and the vorticity distribution is investigated in the vicinity of the turbine. Satisfactory overall agreement is obtained between numerical predictions and measured data on thrust coefficients. The model captures important three-dimensional flow features that contribute to wake recovery behind a vertical-axis turbine, which will be useful for future studies of close-packed rotors with a large number of blades.

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“…A new kind of support structure can be also designed and used in the contra-rotating tidal turbine to improve its performance [14]. The results of the research indicate that the support structure contributes significantly to the behavior of the turbine and to the turbulence levels downstream, even when the rotors are upstream.…”

Section: Introductionmentioning

confidence: 99%

Investigation and Analysis of Attack Angle and Rear Flow Condition of Contra-Rotating Small Hydro-Turbine

2018

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At present, there is strong impetus for renewable energy to replace the traditional energy sources because of the environmental pollution. Small hydropower is a promising renewable energy source; however, small hydro-turbines easily become blocked and impacted, and the efficiency of such devices is lower. Therefore, we examined contra-rotating rotors to overcome these disadvantages. We have made modifications to the blade thickness and to the front hub of the original model. In this paper, we focus on the attack angle and rear flow condition of the original model and the modified one. The axial and circumferential velocities are given as outputs, from which the attack angle is then calculated. The results show that the attack angle of new model is smaller at the hub area. The stagnation point of the rear rotor was moved slightly to the pressure surface of the rear blade, and the separation at leading edge area was suppressed. The crowed flow at the tip clearance area is also reduced. The high turbulent kinetic energy area is moved forward to the middle of the blade. The rear rotor's torque is bigger and changes more smoothly. Therefore, the rear flow conditions of the new model are improved.

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

Cited by 25 publications

References 57 publications

A new tip correction for actuator line computations

A new tip correction for actuator line computations

Aerodynamic Analysis of a Two-Bladed Vertical-Axis Wind Turbine Using a Coupled Unsteady RANS and Actuator Line Model

Investigation and Analysis of Attack Angle and Rear Flow Condition of Contra-Rotating Small Hydro-Turbine

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