Self-induced vibrations on blades/foils that come from eddy currents are a well-known problem in several industries, including the hydropower industry.

It is best known that this problem can occur on stay vanes in hydropower turbines, but the phenomenon can also occur on guide vanes and impeller vanes.

These errors are so rare that it is difficult to gain experience with them, but when they occur it can be critical and lead to a greatly reduced lifetime of the components.

Kristian Sagmo has, in his PhD-work, examined the possibility that rounded serrations on the blades can help dampen vibrations that are formed by current eddies in the water. In addition, he investigated whether the use of vortex generators at the drain edge of the vanes had an effect.

The results from the experiments indicate that vortex generators can dampen the structural vibrations in the interference area, but the "price" you pay for that is increased pressure loss, which in turn can reduce the power production.

The experiments showed, however, that the serrations on the trailing edge can actually amplify the vibrations in the area where the vibrations are formed (the interference area), even if they break up the vortices outside the interference area.

Can lead to increased lifetime in turbines

The results have been tested in the Hydropower Laboratory at NTNU and are currently at an early stage. After any further development, the result can be implemented with turbine suppliers for new deliveries, but also improvements to existing hydro power facilities.

The method has commercial potential as the design methodology can lead to an increased lifetime for turbines and pumps. The methodology can also be delivered as a service for improving existing facilities.

The method has been made available through the publication of several research articles and a doctoral thesis: Trailing edge vortex shedding in hydraulic turbines and the effect of stream-wise vorticity on vortex induced vibrations