Development of a High-Resolution Simulation Methodology for In-Situ Tidal Turbine Performance
— Modeling of Clean Current Tidal Turbines to be placed in the Grand Passage, Nova Scotia —
Kevin W. Wilcox
Jian Tao Zhang
Stanley John
Andrew G. Gerber
Tiger L. Jeans
Department of Mechanical Engineering, University of New Brunswick, Fredericton, NB, Canada
Power and Force Prediction
Realistic Flow Conditions
Bathymetry Where it Counts
In-Situ Turbine Modeling
Blade Element Model
Synthetic Turbulence Generation
Hybrid Immersed Boundaries
Overset Meshing
Modeling rotating turbine blades as part of an in-situ CFD simulation is time
consuming and impractical. Using radial varying lift and drag coefficients determined
by experiment, the Blade Element Model can determine the turbine loading and
power extraction without modeling the individual turbine blades. This greatly
simplifies CFD turbine simulations, making in-situ turbine modeling using real-world
bathymetry a practical endeavour.
The Ocean is not a towing tank. Real-world flows are complex, containing highly
turbulent structures and their effect on loading and power generation needs to be
quantified before installation.
Real-world bathymetry is complicated. Some regions of a domain can significantly
complicate the meshing process and at the same time are not critical to the region of
interest.
Reliable turbine prediction requires modeling turbines in-situ. This is a momentous
task which is complicated by needing a new mesh for each permutation on turbine
position and direction.
Synthetic turbulence introduces spatially and
temporally varying turbulence at the resolved
scales into the flow domain of LES and DES
simulations. This can significantly reduce the size
of the upstream region required for turbulence
development and can allow real-world conditions
to be applied to turbine only simulations.
The hybrid immersed boundary method models the ocean floor in the region of
interest in the traditional method, however, in the non-critical regions, a coarser
In overset meshing the turbine and ocean meshes are developed separately. During
simulation, the two or more meshes are linked through interpolation inside the solver
Good agreement can be seen between the
tow tank experiments and CFD simulations
of the 1.5m Clean Current turbine for ondesign tip speed ratios.
Magnitude of the inlet velocity perturbation field
due to synthetic turbulence at the inlet and
streamlines through the turbine.
Current work injects synthetic turbulence into
turbine simulations with the goal of determining
the effect of turbulence on turbine loading and power generation.
Future work will look to improve the offdesign high tip speed ratio results and
investigate alternate yaw angles.
Bathymetry of the Grand Passage, Bay of Fundy, Nova Scotia. The mesh shaded in blue follows the natural bathymetry present in
the region. In the red shaded regions near the shore the bathymetry is carved out of a structured grid as shown in the call-out.
structured mesh is used where the approximate topology
is carved out of the mesh based on the bathymetry.
Velocity and pressure for the 1.5m Clean Current turbine. A
sharp step in pressure can be observed where the blade
element model extracts energy from the system. RANS
simulation, 5M nodes, structured mesh, 0.005s timestep.
Forces on the blades of the 5m turbine calculated using
the Blade Element Model.
Forces on the hub and shroud of the 5m turbine.
The hybrid immersed boundary meshing method
greatly simplifies mesh generation for complex
Turbine Location
near-shore ocean flows.
Clean Current 1.5m turbine mesh (red) overset on a coarser background mesh (black). Flow freely passes between mesh systems.
at the iteration level. Overset mesh
has been successfully proven with
the Clean Current turbine and
current work will see these turbines
placed in-situ in the Grand Passage
ocean model.
Clean Current 5m turbine shown in-situ in the Grand Passage mesh.
Project Acknowledgement
Velocity plot of the 5m Clean Current turbine wake with an inlet synthetic turbulence boundary condition. The complexity of the
wake is significantly greater than the wake shown to the left for the 1.5m simulation using a constant inlet flow. DES simulation,
5M nodes, structured mesh, 0.005 timestep.
Velocity and direction of flow at the turbine location.
Velocity, 5m depth in the Grand Passage. DES simulation,
24M nodes 2m x 2m horizontal resolution throughout, 0.5m
x 0.5m horizontal resolution in turbine placement region.
The authors would like to acknowledge funding support
provided under a Government of Canada ecoENERGY
Innovation Initiative (ecoEII) with a project titled
“Reducing the cost of in-stream tidal energy generation
through comprehensive hydrodynamic site assessment”.