L.E. Myers

Fundamentals applicable to the utilisation of marine current turbines for energy production

The potential of electric power generation from marine tidal currents is enormous. Tidal currents are being recognised as a resource to be exploited for the sustainable generation of electrical power. The high load factors resulting from the fluid properties and the predictable resource characteristics make marine currents particularly attractive for power generation and advantageous when compared to other renewables. There is a paucity of information regarding various key aspects of system design encountered in this new area of research. Virtually no work has been done to determine the characteristics of turbines running in water for kinetic energy conversion even though relevant work has been carried out on ship’s propellers, wind turbines and on hydro turbines. None of these three well established areas of technology completely overlap with this new field so that gaps remain in the state of knowledge. This paper reviews the fundamental issues that are likely to play a major role in implementation of MCT systems. It also highlights research areas to be encountered in this new area. The paper reports issues such as the harsh marine environment, the phenomenon of cavitation, and the high stresses encountered by such structures are likely to play a major role on the work currently being undertaken in this field.

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

The modelling of tidal turbines and the hydrodynamic effects of tidal power extraction represents a relatively new challenge in the field of computational fluid dynamics. Many different methods of defining flow and boundary conditions have been postulated and examined to determine how accurately they replicate the many parameters associated with tidal power extraction. This paper outlines the results of numerical modelling analysis carried out to investigate different methods of defining the inflow velocity boundary condition. This work is part of a wider research programme investigating flow effects in tidal turbine arrays. Results of this numerical analysis were benchmarked against previous experimental work conducted at the University of Southampton Chilworth hydraulics laboratory. Results show significant differences between certain methods of defining inflow velocities. However, certain methods do show good correlation with experimental results. This correlation would appear to justify the use of these velocity inflow definition methods in future numerical modelling of the far-field flow effects of tidal turbine arrays.

The Effect of Boundary Proximity Upon the Wake Structure of Horizontal Axis Marine Current Turbines

An experimental and theoretical investigation of the flow field around small-scale mesh disk rotor simulators is presented. The downstream wake flow field of the rotor simulators has been observed and measured in the 21m tilting flume at the Chilworth hydraulics laboratory, University of Southampton. The focus of this work is the proximity of flow boundaries (sea bed and surface) to the rotor disks and the constrained nature of the flow. A three-dimensional Eddy-viscosity numerical model based on an established wind turbine wake model has been modified to account for the change in fluid and the presence of a bounding free surface. This work has shown that previous axi-symmetric modeling approaches may not hold for marine current energy technology and a novel approach is required for simulation of the downstream flow field. Such modeling solutions are discussed and resultant simulation results are given. In addition, the presented work has been conducted as part of a UK Government funded project to develop validated numerical modeling tools which can predict the flow onto a marine current turbine within an array. The work feeds into the marine energy program at Southampton to assist developers with layout designs of arrays which are optimally spaced and arranged to achieve the maximum possible energy yield at a given tidal energy site.

Experimental investigation of inter-array wake properties in early tidal turbine arrays

Full-scale marine current energy converter devices have now been operational for several years. These devices have the potential to provide large scale electricity generation when placed in farms/arrays in areas of fast flowing tidal currents. Now the full-scale concept has been proven experienced operators are in a position to provide array developers with devices for such applications, thus at present the first tidal arrays are in the planning and consenting stage around the globe. The inter-device spacing within these arrays can have a profound effect both on the flow field through the array itself and the on the surrounding environment. This paper describes a set of scale experiments aimed at investigating the interaction of devices within an array and potentially highlight some of the pitfalls of future array design which may result in sub-optimal device operation. Experimental results presented herein indicate that particular spacing can lead to regions of accelerated flow which may be exploited to provide greater power production. Further examination of this accelerated flow region is presented, with discourse surrounding the potential issues of placing devices in this region, and impacts the on array geometries as a whole are discussed.