Modelling of the flow field surrounding tidal turbine arrays for varying positions in a channel

Daly, Tim; Myers, L.E.; Bahaj, A.S.

doi:10.1098/rsta.2012.0246

Cited by 12 publications

(9 citation statements)

References 9 publications

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“…However, these methods are not suitable to investigate the wake within 22 and downstream of tidal turbine arrays and focus on the dominant flow processes occurring in 23 such complex operating environments. 24 To reduce the computational resources required to investigate the performance of multiple 1 tidal turbines operating in small arrays, actuator fences (Daly et al, 2013) and multiple 2 circular disks (Nishino and Willden (2013); Turnock et al (2011)) have been used to speed 3 up numerical calculations and investigate the effects of energy extraction for cross stream 4 arrays that block a large proportion of the available tidal channel. It was shown that analytical 5 model and 3D RANS calculation with actuator fence revealed interactions between beneficial 6 flow effects and increased flow reduction due to increasing devices which in turn led to an 7 increased optimum blockage of the tested configurations.…”

Section: Introductionmentioning

confidence: 99%

Three dimensional tidal turbine array simulations using OpenFOAM with dynamic mesh

Nuernberg

Tao

2018

Ocean Engineering

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The flow field characteristics in the wake of an isolated tidal turbine and tidal turbine arrays of up to four devices is investigated by numerical simulations solving the Reynolds Averaged Navier Stokes (RANS) equation in the Open Source OpenFOAM CFD solver to make use of the significantly increased availability of computational resources and multi-core processing. Transient simulations utilizing the k – ω SST turbulence closure model were used in combination with a dynamic mesh interface to account for the rotation of the three bladed tidal turbine at constant tip speed ratio, the applicability of dynamic mesh simulations for the investigation of array wakes has been shown. The velocity and turbulence characteristics are compared to experiments previously conducted with a number of small scale tidal turbine devices arranged in staggered array formations and tested within a low ambient turbulence circulating water channel. Results showed good agreement between simulations and experiments and further insight to the flow field within an array is provided, however further improvements to predict the wake characteristics in array are required

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Section: Introductionmentioning

confidence: 99%

Three dimensional tidal turbine array simulations using OpenFOAM with dynamic mesh

Nuernberg

Tao

2018

Ocean Engineering

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“…Changing the value of K will invariably influence the wake downstream of the disc. The relationship between C T and K has been shown previously using Equation (7). In this paper, K is set to a constant value of 2, which correspond to C T = 0.89.…”

Section: Model Set-upmentioning

confidence: 99%

“…However, because of the strong gradients of the flow and also turbulence variables that exist in the viscous layer, highly-refined grids are needed near the bottom [27]. Small-scale models are known to use a no-slip wall at the bed (refer to References [4,5,7]) since it is still computationally feasible to satisfy the y + requirement. Nonetheless, the flow details in the boundary layer were not of specific interest in this paper.…”

Section: Boundary Conditionmentioning

confidence: 99%

“…This study found that free surface variations may have an influence on the wake and turbine performance. Daly et al [7] examined the methods of defining the inflow velocity boundary condition using ANSYS CFX, and showed that the 1/8th power law profile was superior than others in replicating the wake region. The same software was also used by Harrison et al [5] in comparing the wake characteristics of the Reynolds-Averaged Navier-Stokes (RANS) model against the experimental data measured behind a disc with various porosities, where a detailed methodology on the implementation of the momentum sink was presented.…”

Section: Introductionmentioning

confidence: 99%

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On the Accuracy of Three-Dimensional Actuator Disc Approach in Modelling a Large-Scale Tidal Turbine in a Simple Channel

2018

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To date, only a few studies have examined the execution of the actuator disc approximation for a full-size turbine. Small-scale models have fewer constraints than large-scale models because the range of time-scale and length-scale is narrower. Hence, this article presents the methodology in implementing the actuator disc approach via the Reynolds-Averaged Navier-Stokes (RANS) momentum source term for a 20-m diameter turbine in an idealised channel. A structured grid, which varied from 0.5 m to 4 m across rotor diameter and width was used at the turbine location to allow for better representation of the disc. The model was tuned to match known coefficient of thrust and operational profiles for a set of validation cases based on published experimental data. Predictions of velocity deficit and turbulent intensity became almost independent of the grid density beyond 11 diameters downstream of the disc. However, in several instances the finer meshes showed larger errors than coarser meshes when compared to the measurements data. This observation was attributed to the way nodes were distributed across the disc swept area. The results demonstrate that the accuracy of the actuator disc was highly influenced by the vertical resolutions, as well as the grid density of the disc enclosure.

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“…Above and below the turbine, the flow was less affected by the presence of the turbine, but the mean current strength was still weaker than predicted in the absence of turbines. These profiles do not have the large velocity deficit at the turbine and the accelerated flow beneath the turbine predicted by computational fluid dynamics (CFD) models e.g., [38] because the velocities are volume-averages. However, previous work [33] has shown that the averaged velocities from a CFD model are very similar to the averages derived by the larger scale model used here.…”

Section: Turbine Effects On Velocity Profilesmentioning

confidence: 99%

Numerical Simulations of the Effects of a Tidal Turbine Array on Near-Bed Velocity and Local Bed Shear Stress

Gillibrand

Walters²,

McIlvenny

2016

Energies

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Abstract:We apply a three-dimensional hydrodynamic model to consider the potential effects of energy extraction by an array of tidal turbines on the ambient near-bed velocity field and local bed shear stress in a coastal channel with strong tidal currents. Local bed shear stress plays a key role in local sediment dynamics. The model solves the Reynold-averaged Navier-Stokes (RANS) equations on an unstructured mesh using mixed finite element and finite volume techniques. Tidal turbines are represented through an additional form drag in the momentum balance equation, with the thrust imparted and power generated by the turbines being velocity dependent with appropriate cut-in and cut-out velocities. Arrays of 1, 4 and 57 tidal turbines, each of 1.5 MW capacity, were simulated. Effects due to a single turbine and an array of four turbines were negligible. The main effect of the array of 57 turbines was to cause a shift in position of the jet through the tidal channel, as the flow was diverted around the tidal array. The net effect of this shift was to increase near-bed velocities and bed shear stress along the northern perimeter of the array by up to 0.8 m·s −1 and 5 Pa respectively. Within the array and directly downstream, near-bed velocities and bed shear stress were reduced by similar amounts. Changes of this magnitude have the potential to modify the known sand and shell banks in the region. Continued monitoring of the sediment distributions in the region will provide a valuable dataset on the impacts of tidal energy extraction on local sediment dynamics. Finally, the mean power generated per turbine is shown to decrease as the turbine array increased in size.

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Modelling of the flow field surrounding tidal turbine arrays for varying positions in a channel

Cited by 12 publications

References 9 publications

Three dimensional tidal turbine array simulations using OpenFOAM with dynamic mesh

Three dimensional tidal turbine array simulations using OpenFOAM with dynamic mesh

On the Accuracy of Three-Dimensional Actuator Disc Approach in Modelling a Large-Scale Tidal Turbine in a Simple Channel

Numerical Simulations of the Effects of a Tidal Turbine Array on Near-Bed Velocity and Local Bed Shear Stress

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