A modified implementation of actuator line method for simulating ducted tidal turbines

In this numerical study, the standard actuator line method is modified for simulating ducted tidal turbines and validated against experimental data for two turbines with different geometries. The necessary modifications, which are based on the unique features of ducted turbines, include using a grid-based distribution of blade elements, employing the local chord length as the length scale for the projection factor, and implementing a cylindrical projection. This study also provides a guideline to facilitate choosing the projection factor, the only parameter in the actuator line method which is chosen empirically. The first ducted tidal turbine studied in this work is the Cresswell turbine, the operation of which is simulated at its design tip speed ratio in axially aligned and yawed onset flows. The second turbine, developed by Clean Current Power Systems, is simulated over a range of tip speed ratios in axially aligned onset flow. In order to study the effect of the turbulence model on the actuator line method's predictions, for this turbine, both the detached eddy simulation and k to turbulence models are employed and the results are compared. Importantly, the actuator line methodology presented here is implemented in a heterogeneous CPU/GPU architecture making in-situ simulations of tidal turbines feasible.