Aspects of tidal stream turbine modelling in the natural environment using a coupled BEM–CFD model

Abstract

Marine Renewable RANS BEM CFD Wake Shadow Nacelle Tower Contrarotating Turbulence Power Headland Fence Blockage Stream surface a b s t r a c tThe problem of designing the optimal array of tidal stream turbines for the generation of marine renewable energy from the ocean, raises a number of questions about the distribution and layout of turbines in relation to the local bathymetry. The computational overhead of modelling such problems may be significant and costly. This paper aims to clarify the effects of particular phenomena associated with modelling tidal stream turbine arrays. To achieve this we use a RANS computational fluid dynamics model with an embedded blade element actuator disk to investigate various aspects of this problem, while maintaining reduced computational overhead.A study of axially aligned turbines, with each in the wake shadow of the previous turbine shows uniform effects for a 20 diameters downstream spacing, but more complex interaction for 10 diameters spacing. Investigation of the significance of inclusion of the nacelle and tower geometry in a CFD model shows that effects are negligible beyond six diameters downstream. An array of transverse contrarotating turbines are considered, where a device is placed close to and in the wake of a pair of upstream devices. Rotational direction has minimal effect on the power generated, but different turbulence is seen in the wake. Finally, marine currents around a headland are modelled and a single row fence of turbines is placed offshore from the headland at various blockage ratios. Power performance estimates and downstream wakes are created and they show increased power per device and improved total power production as the blockage ratio rises from 0.13 to http://dx.

A Comparison of Numerical Modelling Techniques for Tidal Stream Turbine Analysis

“…Rather than representing the geometry of the turbine directly as in the CFD model, we treat the rotor as a momentum source/sink in the domain based on the geometry and hydrodynamic properties of the blade. This BEM-CFD method has been validated in the previous research of the group, together with a mesh independence study [25].…”

“…In the comparison between these two models, we are primarily interested in the velocity deficit in the turbine wake. An understanding of turbine wakes is vital if tidal turbines are to be deployed in arrays [24] (as turbine wakes will inevitably impinge on other turbines located downstream), and such arrays are the only way tidal turbines can be economically viable [25].…”

“…The scenario tested in this paper was based on [49] and the BEM-CFD case more fully described in [25]. The domain was 770 m wide for both cases with the headland extending by 230 m. The offshore boundary was set to full slip condition in both cases.…”

Deployment characterization of a floatable tidal energy converter on a tidal channel, Ria Formosa, Portugal

“…The effect of mooring lines on the seabed is restricted to a few centimetres at both sides of the mooring lines; carried out in laboratories [22][23][24] i.e. in the few cases that devices have been deployed and monitored data are highly commercially sensitive and not distributed to the public and research community [25,26]. A full characterisation of the 3D flow patterns was performed using ADCPs (moored and boat-mounted surveys).…”

A Numerical Methodology for Simple Optimization of Marine Hydrokinetic Turbine Array

“…Harison et al [12] investigated The effect of ambient turbulence on the inter-row spacing and reported that an increased ambient upstream turbulence decreases the wake recovery length and thus the required inter-row spacing decreases. Also, if it is practical, it is proposed that the downstream distance increases to 75% of wake velocity recovery distance to ensure consistent wake recovery and thus consistent power extraction of downstream devices [13,14]. From practical point view, it is not beneficial to increase downstream distance unlimitedly, because reducing the distance between turbines has several advantages shorten the submarine cable length, efficient utilization of ocean space, lower the difficulty of tidal power farm construction, and so on [15].…”