Cavitation causes flow instabilities that hampers the functioning of flow devices, primarily by increasing the noise level, vibration, and, in extreme cases, the devices’ erosion.

Experimental tests have been carried out on two Magallanes tidal turbines. By tuning the turbines’ external pitch angle, we can achieve the “load-balancing” in terms of power output from both the turbines.

Optimizing the turbine geometry requires rigorous investigation of hydrodynamic behaviour of blades and their interaction with the supporting structure and nacelle. SSPA has performed experimental tests in order to provide a baseline for further improvement of the blade design by evaluating the performance of the model turbine and measuring the flow field using Laser Doppler Velocimetry (LDV) method.

Tidal turbines play a crucial role in providing sustainable and pollution-free energy. In tidal turbines, cavitation is an important phenomena in determining the life span of the turbines.

NEMMO project partner Technion (Israel Institute of Technology) has developed and performed a high-order Large Eddy Simulations (LES) code, called MIRACLES, to study cavitation sheet dynamics associated with the modified scaled-down Francis turbine (hydrofoil) at angle of attack (AOA).

This research paper focuses on elucidating and analysing the re-entrant jet dynamics. Active cavitation control via steady wall jet injection was studied, but it had limited effect for the flow conditions (injection velocities and AOA) considered.

The results of this study are now available on the ScienceDirect: Interaction between surface blowing and re-entrant jet in active control of hydrofoil cavitation.

Further study on LES of wind (and tidal) turbines using a Filtered Actuator Line Model (ALM) has been carried out based on the outcome of the previous study. This study encourages accurate and affordable simulations of multirotor devices in the future.

The result of this study is now available on the ScienceDirect: Large-Eddy Simulation of a wind turbine using a Filtered Actuator Line Model.

The NEMMO project team have designed and built novel test-rigs to define the best AFC (Active Flow Control) strategies for improving the performance of tidal turbine blades.

Tailor-made testing procedures were developed to carry out a sizeable experimental test programme in SSPA’s cavitation tunnel. These testing procedures for integrated harsh marine stresses enable the replication and modelling of composites blades’ lifespan, cavitation wear rates, bio-fouling growth, ageing in a harsh marine environment and hydrodynamic performance.

Developing novel materials and coatings for tidal turbine blades is one of the main objectives of the NEMMO project.
Three parallel approaches have been used to enhance blade material performances in order to increase their ageing, fouling, impact, and cavitation resistance:

• Improving the fatigue and impact resistance of the new nano-enhanced composite materials.
• Controlling biofouling by means of blade surface micro-texturing.
• Developing novel non-leaching anti-fouling coatings with permanent cavitation resistance through the design and synthesis of polymers bearing different functionalities within its chemical backbone and the incorporation of functionalized nanoparticles into such polymer formulations.

Part of the NEMMO project has been dedicated to designing an effective texture tailored to the NEMMO turbine. Bio-inspired surface modification has shown potential as an antifouling strategy. The surface textures can act on the ability of fouling micro-organisms to find secure attachment to the substrate but also alters fluid induced stresses over the organisms. The two effects combine to reduce initial settlement and improve the self-cleaning properties of the surface by altering cell adhesion in turbulent flows.

The NEMMO project team has recently published novel composite material solutions to enhance the resistance of tidal turbine blades. Key test results are presented along with an outline description of the methodologies adopted. This study focuses on three parallel approaches adopted to enhance blade material performance.

This research helps the NEMMO project reach its ambitious targets to drive down maintenance costs due to cavitation wear, bio-fouling and ageing, and to enhance hydrodynamic performance.