Refined representation of turbines using a 3D SWE model for predicting distributions of velocity deficit and tidal energy density

Abstract

SUMMARYEnergy sustainability has become one of the most concerned issues around the world, and tidal stream power is one of the promising types of renewable energy with merits of high predictability, relatively low cost, and low environmental impact. Numerical models based on the shallow water equations (SWE) have been applied to assess the energy distribution and environmental impact. In existing SWE models, the effect induced by tidal stream turbines on the fluid is usually represented by bed friction, which is only applicable for far-field studies. In the current study, a Blade Element Momentum (BEM) model has been developed and integrated into a three-dimensional (3D) SWE model to improve the accuracy for assessing tidal current energy distributions. Using the BEM approach, state variables can be obtained for a blade element of a turbine rotor. These state variables can be used to calculate the local thrust coefficient, which is introduced for representing the effect of rotors in the 3D SWE models. A 3D SWE model has been refined, by incorporating the proposed BEM model, to simulate the density distribution of a tidal turbine farm. The refined SWE model has been validated against measurements from a flume experiment of turbine arrays. The model performs generally well in predicting the distribution of velocity deficit and the recovery of wakes. In a field-scale application to a planned tidal power test site, the model was used to predicting the flow field for both a single turbine scenario and a turbine array scenario.

Implementation of a Full Momentum Conservative Approach in Modelling Flow Through Tidal Structures

“…Future work could consider increasing the number of layers of the 3D model. For example, a study by Lin et al [46] employed ten computational layers to model adequately the wake behind a tidal stream farm. However, each additional horizontal layer adds to the total computational time and makes the regional model less attractive for practical use and with limitations on the resources available for only a slight increase in the accuracy of the predictions.…”

“…The same approach in modelling tidal stream turbines, where momentum sink was represented by an external force equal and opposite to the thrust force exerted by the flow on the propeller, has already been introduced to Delft3D by several authors in Ref. [45,46]. While the approach of momentum sink within the computational domain is already commonly used in tidal stream studies, the momentum source represents a novel method of modelling the TRSs and other hydraulic structures.…”

Hydrodynamic modelling of tidal range energy

“…They are derived from the large-scale oceanic models and can employ hydrostatic or non-hydrostatic forms of Navier-Stokes equations (Marshall et al 1997). At the time of writing, the use of a 3D hydrostatic model on a regional scale has been limited to the modelling of tidal stream extraction (Lin et al 2015;Rahman and Venugopal 2015). Both studies employed a Delft3D model, where tidal stream turbines were modelled as an actuator disk -a methodology commonly used with wind turbines.…”

Vertical-Axis Tidal Turbines: Model Development and Farm Layout Design

“…To the best of the authors' knowledge, there are only two examples (using a regional code) of turbine models that use the momentum sink approach coupled with a Blade-Element\Momentum (BEM) model to represent the turbines. The first example is that developed in [12] in the Delft3DFlow code. The second is the model developed for the regional code SHYFEM, as described in [13].…”