Kaplan Turbine: Hydrodynamic Performance and Wake Evaluation

Kaplan Hydro Turbine Evaluation, ANSYS Fluent CFD Simulation Tutorial

Description

This project evaluates a Kaplan hydro turbine using ANSYS Fluent. The Kaplan turbine is a propeller-type water turbine featuring adjustable blades, classified as an inward-flow reaction turbine — meaning the working fluid undergoes a pressure change as it passes through the turbine, giving up its energy in the process. Power is recovered from both the hydrostatic head and the kinetic energy of the flowing water, with the Kaplan design combining characteristics of both radial and axial turbines.

This project studies the turbine's hydrodynamic behavior, with the rotor set to an angular velocity of 16.5 rpm. Boundary conditions include a constant mass flow rate of 1000 kg/s at the inlet, zero gauge pressure at the outlet, and symmetry conditions applied to all side walls, given their distance from the region of primary interest. The study also evaluates turbine performance through the resulting drag force.

The geometry — a small-scale Kaplan turbine — was designed in Design Modeler and meshed in ANSYS Meshing using an unstructured grid totaling 9,861,922 cells.

Methodology

Turbine rotation was modeled using the MRF (Moving Reference Frame) approach via the Frame Motion option, treating the fluid surrounding the turbine blades as rotating rather than the blades themselves. Given the turbomachinery nature of this simulation, a dedicated cylindrical zone was separated from the broader computational domain, with the fluid within this zone assigned a rotational velocity matching the turbine's own, implemented through the MRF tool within Cell Zone Conditions.

Conclusion

Results include 2D and 3D contours of pressure, velocity, and surface pressure, along with velocity vectors and streamlines illustrating the fluid's rotational motion around the turbine blades.

The lowest pressure occurs at the turbine's leading edge, consistent with the highest velocity values occurring at the blade tip. Velocity contours further show that rotational velocity — and the influence of the associated source terms — increases with distance from the turbine axis. The pressure distribution along the turbine walls forms two distinct regions: a high-pressure zone upstream, before the flow interacts with the turbine, and a corresponding low-pressure zone downstream, behind the turbine geometry.

The flow vectors also capture the wake region's resolved behavior — a central challenge in aerodynamic simulation of this kind — revealing a suction mechanism active at the turbine's lower sections and a blowing mechanism at the upper sections. A core vortex adjacent to the turbine body is likewise captured, offering insight into how the flow field is reshaped in close proximity to the rotating walls.