R&D In Tidal Turbines Using CFD

Discover the techniques applied to tidal turbines through the use of Computational Fluid Dynamics (CFD).

Understanding Tidal Energy and Turbines

Tidal energy is a form of renewable energy generated from the movement of ocean tides, and tidal turbines harness this energy to generate electricity. These turbines are similar to wind turbines, but instead of using wind, they utilize the power of ocean currents. The predictability of tidal currents and ocean streams implies that underwater power stations could contribute to the base load power supply, generating energy consistently. This presents a notable advantage compared to other unreliable or sporadic renewable energy options.

Researchers and engineers need to study the behavior of tidal currents, the impact of turbines on the marine environment, and the overall performance of the turbines to optimize their design and operation. Currently, there are different projects around the world in various stages of development. Some of the most important projects are mentioned by the OES (Ocean Energy Systems) in the document '2023 Tidal Current Energy Developments Highlights'.

• MeyGen, 6 MW up to 34 MW (north of Scotland)
• Nova Innovation Tidal Array, 600 kW up to 1.5 MW (Shetland, Scotland)
• Verdant Power, 210 MWh generated (New York's East River, USA)
• Sustainable Marine Energy, 420 kW up to 1.26 MW (Nova Scotia, Canada)
• Orbital Marine Power, 2 MW (The European Marine Energy Centre, United Kingdom)

Importance of R&D

In addition to tapping into wind and solar energy, capturing the immense kinetic energy found in the Earth's tidal currents, ocean currents, and river flows represents one of the most encouraging prospects for renewable energy sources. However, these types of devices are still expensive as they face the challenge of cost-effectiveness. According to the International Energy Agency (IEA), ocean power generation in the NetZero Scenario 2000-2030 requires an energy generation of 27 TWh by 2023, but it only reached 1.6 TWh in 2020.

In general, R&D must be focused on the mitigation of flow separation and drag and include optimization to avoid trial and error. The study of Fluid-Structure Interaction (FSI) and new materials is also needed to increase the lifecycle. Moreover, R&D helps in understanding the environmental impact of tidal turbines and finding ways to minimize their effects on marine ecosystems. It also allows for the exploration of innovative approaches and solutions to overcome the challenges faced in tidal turbine deployment and operation.

Role of Computational Fluid Dynamics

Computational Fluid Dynamics (CFD) is a powerful tool used in the design and optimization of ThermoFluid systems and Turbomachines. By using CFD, engineers can simulate various operating conditions and evaluate the impact of different factors. In general, engineers pursue crucial information for designing robust, reliable, and cost-effective tidal turbine systems. Therefore, CFD capabilities include,

• Simulate and analyze the flow of water around the turbine blades, predicting their performance and efficiency.
• Optimize the blade shape, size, and orientation.
• Include the effects of water depth, turbulence, and sediment transport, on the performance of tidal turbines. 
• Maximize net energy output and peak power generation while maintaining highest degree of safety​. 
• Address challenges that are unique to tidal applications and explore environmental impacts for design of high-capacity, durable tidal turbines.
• Ensure structural integrity of the turbines can be optimized for both operating conditions and extreme events​, and increasing durability will in turn reduce maintenance and replacement costs.

Another area of innovation in R&D for tidal turbines is the development of floating turbine systems. Traditional tidal turbines are fixed to the seabed, which limits their deployment to shallow waters. Floating turbines, on the other hand, can be deployed in deeper waters, opening up new areas for tidal energy extraction. For these applications, it is required to analyze the effects of waves, currents, and other environmental loads on the moorings, as well as on the stability of tidal turbine structures. Here, it must be defined whether viscous-dominated problems are of interest (such as breaking waves and turbulence). The images below present an example in which the loads (left) are defined to calculate the pressure (middle) that is transferred to FEA (right).

Ultimately, investing in R&D for tidal turbines is important for the growth of the renewable energy sector and the transition towards a more sustainable and clean energy future. The future of tidal turbine technology looks promising, with CFD playing a significant role in its development. As computational power and modeling techniques continue to advance, the accuracy and speed of CFD simulations will improve, enabling more detailed and reliable predictions of turbine performance.

Success Case

An earlier generation of experimental marine power generators used a shrouded propeller with blades that were supported only where they connect to the shaft. However, resulting stresses on the blades led to failures, and the search for solutions has resulted in the use of expensive materials. Gilmore Engineers Pty Ltd was contracted to optimize the design of a new generation of tidal current power generators in which the outer diameter of the rotor blades is connected to the shroud to reduce those stresses on the blades. Below are outlined the most important points.

CAD model of the marine power generator and the CFD results (Pressure on the surface of the power generator with velocity streamlines).

CFD: Technology capabilities

• Engineers then simulated the blades in steady-state mode using the Ansys CFD frozen rotor model to connect the rotating components to the optimized shroud design.
• Ansys CFD software was used to simulate about 30 sizes and shapes of the shroud in a week, focusing on the diffusor or draft tube region, to determine the design that provided the lowest pressure while maintaining flow attachment to the wall.
• Further analysis was then performed on the best-performing shapes by varying the size, shape and number of slots and taking into account production costs.
  
  

Results: Design improvements

• The design optimized by CFD generated 3,892 W, an improvement of nearly 150% over the initial design.
• The complete design optimization took 96% less time than would have been required using the build-and-test method. 
• The initial design of this tidal current power generator was limited because it produced so much turbulent kinetic energy (left). Using Ansys CFD, engineers optimized the final design to generate power much more efficiently (right).