Francis Turbine: Acoustics Analysis

Francis Turbine Acoustics Analysis, ANSYS Fluent CFD Simulation Training

Description

Francis turbines are a type of water turbine capable of harnessing both kinetic and potential energy simultaneously for power generation, owing to the specific arrangement of their blades. Water flows into the turbine's spiral chamber, where the circular arrangement of the blades requires the incoming fluid to adopt a rotational flow pattern as it collides with them, improving overall operational efficiency. This rotational flow is then directed onto the turbine runner blades at a defined flow rate, driving their rotation and producing the desired mechanical work, with water ultimately exiting the runner blades in an axial direction.

This simulation models water entering the turbine's inner chamber at a mass flow rate of 1.996 m/s, with the runner blades rotating at 158 rpm.

The geometry was designed in Design Modeler around two main components: fixed walls carrying stationary vanes set at fixed angles, and moving walls carrying the rotating runner blades. The domain was meshed in ANSYS Meshing using an unstructured grid totaling 4,914,404 elements, with finer mesh resolution applied near the blade surfaces to capture the more complex local flow behavior.

Methodology

Blade rotation within the chamber, and the resulting rotational flow field around the blades, was captured using the Moving Reference Frame (MRF) approach — the water flow region surrounding the blades is treated as rotating relative to the blades themselves, while the blades are assigned zero rotational speed relative to this rotating reference frame. Acoustic behavior was modeled using the Broadband Noise Sources model.

Conclusion

Since this simulation builds on an established turbomachinery configuration already characterized in prior hydraulic analysis, the acoustic investigation here proceeds directly from those same flow settings. The results show that the rotating runner blades contribute the larger share of sound generation within the system, exhibiting notably higher acoustic power in the corresponding contour compared to the stationary components.

The linearized Euler equations' contour further illustrates how sound propagates through the space between the rotor and stator, offering insight into the acoustic wave transmission pathway within the turbine's internal geometry — information directly relevant to understanding and potentially mitigating turbine noise in real-world hydroelectric installations.