Numerical simulation of ducted and non-ducted tidal turbines using actuator line method
University of New Brunswick
Electricity generation using tidal turbines is a relatively new technology in the renewable energy field. These turbines, due to their harsh and complex operational environment, must be engineered to operate with low maintenance and high efficiency. Therefore, significant research and development is being undertaken to achieve these operational goals, and high fidelity numerical tools such as CFD are being applied to the problem. However, tidal flows are very site-specific and only in-situ simulations can give a reliable estimate of a turbine's performance and the imposed forces on its components. In this thesis, the actuator line (AL) method is investigated as a method feasible for in-situ simulation of tidal turbines in high resolution CFD simulations. The AL method does not require a detailed treatment of the turbine blade geometry but incorporates its rotational effects on the flow. It therefore becomes more computationally efficient while also maintaining the ability to include dynamic loads and wakes. Therefore, in this work the AL method has been developed in a heterogeneous CPU/GPU parallel architecture and its implementation has been validated by simulating a well-studied non-ducted tidal turbine at different tip speed ratios (TSRs) in straight and yawed flows and investigating the turbine's parameters and wake. Next, considering the popularity of the ducted design in tidal turbines, and the fact that presently there appears to be no study on applying the AL method to ducted turbines, an important goal of this work has been to extend the AL method for simulations of ducted turbines. This has been done by investigating two ducted tidal turbines and revising the method based on the unique features of ducted turbines. This in particular includes using the grid-based distribution of blade elements and the cylindrical projection of the imposed force on each blade element. Improving the projection process by using the local chord length as the length scale for the projection factor and providing a guideline for choosing this factor have also been carried out. This thesis also includes comprehensive discussions on generated wakes and predicted power and thrust coefficients for these two turbines in different conditions.