Water Wheel (Pelton)

Water Wheel (Pelton Wheel), ANSYS Fluent CFD Simulation Training

Description

This project simulates the performance of a water wheel — a classic example of a Pelton turbine — using ANSYS Fluent.

Most water wheels are mounted vertically on a horizontal axis, though horizontal mounting on a vertical shaft is also possible. The fluid flow equations are solved using the averaged form of the Navier-Stokes equations within ANSYS Fluent.

The turbine has a diameter of 0.7 m, with the free surface boundary positioned 0.2 m below the wheel's center. Water velocity ranges between 3 and 5 m/s, depending on average river conditions, from which the turbine's rotational speed is determined to avoid drag or disruption in the flow — in this simulation, the turbine rotates at 60 rpm.

Methodology

The wheel's blades are positioned perpendicular to specific turbine sections to reduce friction and increase nozzle thrust, while a portion of the turbine remains outside the water. As a result, the wheel operates across two distinct phases — water and air — as it rotates about its axis, modeled using the VOF (Volume of Fluid) multiphase model.

The turbine geometry was designed in SOLIDWORKS and divided into smaller sections to improve both geometric detail and mesh quality. The model was split into two rotating (Rotor) regions and one stationary (Stator) region: the rotor comprises the turbine itself along with a surrounding cylinder, while the static region encloses this rotating cylinder.

Meshing was performed in ICEM CFD. The rotor section was meshed using an unstructured grid, with finer mesh density applied at the turbine's leading edge to capture the complex flow behavior and high gradients present in that region. The stationary zone used a structured mesh, which reduces overall element count while maintaining high mesh quality. The two separately meshed regions were then coupled together to form the complete domain.

Impeller rotation was applied incrementally, with 3 degrees of rotation per time step — a value that should be reduced further for higher simulation accuracy. This motion was handled using the Mesh Motion approach, with the static and rotating mesh regions sliding relative to one another across a shared interface boundary.

Conclusion

The results clearly capture the wheel's continuous rotational motion as it interacts with the incoming water stream, with velocity and pressure contours highlighting how the flow strikes each bucket in sequence to sustain the wheel's rotation. The VOF-based volume fraction contours trace the air-water interface as it deforms around the submerged buckets, showing the free surface dipping and recovering as each bucket enters and exits the water.

Pathlines around the turbine illustrate how incoming flow is redirected by the curved bucket geometry, transferring momentum to the wheel and producing the torque that drives its rotation. Together, these results confirm that the coupled rotor-stator mesh motion setup successfully reproduces the expected physical behavior of a Pelton-type water wheel operating at the free surface, providing a validated basis for evaluating design changes such as bucket geometry, submersion depth, or rotational speed in further studies.