Electrical & Power: Francis Turbine

Description

This project simulates the water flow through a Francis hydraulic turbine using ANSYS Fluent. As a cornerstone of hydroelectric power generation, a water turbine is a turbomachine that converts the kinetic energy of flowing water — or the potential energy stored in a head (height) difference — into mechanical rotational motion, which is subsequently transformed into electrical power by a coupled generator.

The Francis turbine is one of the most widely deployed turbine types in power plants because the arrangement of its blades allows it to harness kinetic and potential energy simultaneously, making it highly effective across a broad range of head and flow conditions.

In operation, water first enters the volute (spiral casing), whose circular geometry imparts a rotational (swirling) component to the incoming flow. This swirl ensures the fluid strikes the blades at the correct angle, maximizing operational efficiency. The flow is then delivered at a controlled rate to the runner blades, where the momentum of the water drives the runner and produces useful mechanical work. Finally, the water exits the runner in an axial direction.

In the present case, water enters the turbine's inner chamber at a mass flow rate of 1.996 kg/s, with the runner blades rotating at 158 rpm.

Methodology

The rotation of the blades is modeled using the Multiple Reference Frame (MRF) approach, also known as frame motion. In this method, the fluid region surrounding the blades is assigned a rotational motion, while the blades themselves are held stationary relative to that rotating frame — effectively reproducing the rotational flow field around the runner without physically moving the mesh.

The geometry was built in Design Modeler and consists of two main components: fixed walls carrying stationary vanes at fixed angles, and moving walls carrying the rotating vanes.

Meshing was performed in ANSYS Meshing using an unstructured grid of 4,653,160 elements, with local refinement applied near the blades to better capture the flow behavior in these critical regions.

Conclusion

On completion of the solution, two- and three-dimensional contours of pressure, velocity, path lines, and velocity vectors were extracted. As expected, the peak velocity occurs in the immediate vicinity of the rotating blades. A full set of performance results can be derived from the simulation, including a pressure drop of approximately 2.3 × 10³ Pa across the turbine.