CFD FOR WIND AND TIDAL OFFSHORE TURBINES
|Author(s)||Esteban Ferrer, Adeline Montlaur|
Problems where the forces on rotating or oscillating bodies in a fluid are to be predicted are common in engineering applications and result in fluid-structure interaction situations. Examples are flows around isolated rotating bodies and foils, turbo machinery applications, insect flight aerodynamics, unmanned air vehicles and, more recently, flows through renewable energy devices, e.g. wind and tidal turbines. A particularly challenging problem is presented by cross-flow wind and tidal turbines for power generation. These types of turbine consist of foil shaped blades that generate lift forces so as to rotate a shaft to which the blades are connected. Therefore azimuthal changes in blade aerodynamics are common, resulting in complex flow phenomena such as stalled flows, vortex shedding and blade-vortex interactions. Cross-Row Turbines are sometimes referred to as vertical-axis turbines, however the term cross-flow turbine is preferred since the absolute turbine position is omitted and the relative flow-axis geometry is emphasised through this terminology. To date, this type of turbine configuration has had limited use within the wind energy sector, where the three bladed axial flow turbine has been widely adopted. However, it is thought that CFT configurations can be advantageous for new emergent markets as offshore wind and tidal energy production and also for installation in urban environments. A brief review of some of the arguments in favour and against this type of configuration follows. On the one hand, the main drawback is that CFT are generally less efficient than axial flow turbines since the downstream half of the turbine produces less torque due to the shadowing from the upstream blades. Furthermore, since for part of the cycle the blade moves parallel to the flow, the lift force powering the blades, being proportional to the incident flow speed squared, is reduced...
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