Potential assessment study as a basis for deciding

on refurbishment measures for a vertical Kaplan turbine

We are currently working on a CFD-based potential assessment study for a well-known German energy supplier. The results and findings of this study will serve as a basis for decisions on the implementation of refurbishment measures.

Initial situation

The plant, which went into operation in 1961 and whose two vertical Kaplan turbines are still more or less in their original condition, is to undergo extensive renovation next year.

Due to significant cavitation damage to the runner blades and the outer ring, the following two optimisation options are available:

• Option 1: Blade optimisation while retaining the existing hub and the existing contour of the turbine casing – this could simply be refurbished.

• Option 2: Blade optimisation while retaining the existing hub, but in combination with a NEW, extended contour of the turbine casing.

As a starting point for the investigation, the flow contour of the entire turbine was measured on site using a 3D scanner and modelled accordingly based on the scan data. In the next step, a 3D CFD study of the existing turbine configuration was carried out to identify the shortcomings of the current situation – see flow visualisations in the figure below.

Further procedure

For both optimisation options, optimised Kaplan runners are currently being developed, which will be used to numerically investigate the performance curves at nominal head.

In the next step, the predicted annual working capacity and the percentage increase compared to the current situation are determined with the help of the annual hydrograph and production data from previous years.

This approach serves as the basis for decision-making regarding the most economical renovation measures for the existing hydropower plant.