Marine: Water Turbine, Horizontal Axis

Description

This study investigates water flow over the blades of a Horizontal Axis Water Turbine (HAWT) using ANSYS Fluent, with the goal of examining the velocity and pressure distribution across the blade surfaces. Turbines of this kind are central to marine and hydrokinetic energy engineering, where they harness the kinetic energy of moving water to generate power.

Two regions are defined around the blades: a cylindrical zone immediately surrounding them, and a larger domain enclosing that cylinder. In the outer domain, the water behaves as an ordinary free stream, while in the inner cylindrical region the rotational motion of the blades induces a swirling, rotational flow.

Several assumptions underpin the simulation. The analysis is steady-state, since the turbine is of the horizontal-axis type and time therefore has no bearing on the drag and lift forces. A pressure-based solver is used, and gravitational force is neglected.

Methodology

The model was built in 3D, with the blade cross-section based on an S814 airfoil whose coordinates were taken from the Airfoil Tools website and exported as a text file. Because the airfoil section scales up or down along the blade span, Excel was used to define the coordinates at each spanwise station. Each section was then drawn in SOLIDWORKS at the appropriate angle and position and imported into Design Modeler to construct the blades and turbine shaft. Within Design Modeler, the rotational water region around the blades and the larger free-stream domain were both created.

Meshing was performed in ANSYS Meshing using an unstructured grid. To improve accuracy, a boundary-layer mesh was applied to the blade surfaces, and the final cell count reached 4,270,222.

The rotation of the blades is modeled using the Frame Motion (MRF) method. The turbine blades rotate at 191 rpm while the surrounding water is treated as stationary; under this approach, the blades are held fixed and the water region around them is assigned a rotating frame turning at the same 191 rpm about the Z-axis. Because the simulation is steady-state, the Mesh Motion option is disabled — it applies only when time-dependent effects must be captured, whereas here the objective is simply to impose the rotational speed on the blades.

The solution setup is summarized below:

Viscous model — SST k-omega

Boundary conditions — velocity inlet at 1 m/s; pressure outlet at 0 Pa gauge; all walls set as stationary

Solution methods — SIMPLE pressure-velocity coupling; second-order upwind discretization for pressure, momentum, turbulent kinetic energy, and turbulent dissipation rate

Initialization — standard method, with an initial velocity of −1 m/s in the Z-direction

Conclusion

On completion of the solution, the velocity and pressure distributions over the turbine blades can be examined in detail through the corresponding contours. These results reveal how the water loads the blade surfaces and how the rotational flow develops within the cylindrical zone, providing the basis for evaluating the hydrodynamic performance of the horizontal-axis water turbine.