PDL engineers supported the development of a world class test facility for tidal turbines; the Nautilus Rotary Test Rig. This DECC funded project culminated in the manufacture of a 3MW onshore rig, complete with actuation systems capable of replicating the loads a turbine will be subjected to subsea, the benefit to tidal power developers being the significant reduction in risk through the ability to fully test their devices onshore during the development phase.
PDL engineers provided computational fluid dynamics (CFD) consultancy support to the project through the development of validated models using the ANSYS CFX package complete with a customised graphical user interface (GUI) and a sub-modelling approach.
The CFD approach was adopted in order to allow the designers of the Nautilus to validate the magnitude of loads that would typically need to be applied during testing, and would subsequently be used by Nautilus clients to validate the specific loads their device would be subjected to when installed in a specific location.
The project consisted of a number of phases;
1. The selection of a test site; the Fall of Warness in Orkney which is also the location of the European Marine Energy Centre (EMEC)
2. Deployment of acoustic Doppler current profiler devices (ADCP) to measure actual current velocity through the water column in the test site that could be utilised for model validation.
3. The creation of a 3D CFD model representing a 3000 x 3000m portion of the site, to water depths determined from commercial bathymetry data. This included an automated meshing routine with blockage techniques included for land masses.
4. Interpolation of the ADCP data to allow water velocities throughout the model to be predicted.
5. Generation of a sub-model representing a smaller fluid domain containing a representative tidal turbine.
Each of the analytical phases included significant attention to model optimisation and sensitivities, always with a view to the future use of the derived techniques when applied to commercial projects.
Validation of the sub-model was completed through a test case representing work conducted by the University of Southampton in their cavitation tunnel.
The project concluded having succeeded in determining design load magnitudes, with a validated wide area CFD approach and a sub-model capable of representing common tidal turbine models and determining loads the device would be subjected to when deployed in specific locations.
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