PIV measurement of the flow in the vaneless space of a Francis Turbine

As the demand for green energy increases, so does the investment into clean energy sources. Especially the amount of solar and wind energy produced are growing at a rapid pace. While their cost is decreasing, they remain what is referred to as unreliable energy sources. This might emphasise hydropower s role as a power grid balancer, forcing turbines to operate at transient conditions. Both in the form of reoccurring start-stop cycles as well as part-load operations. The most frequently used hydropower turbine, the Francis turbine, is sensitive outside of its design condition. Not only do minor changes quickly reduce efficiency, it also has a history of causing fatigue, noise and cracks in internal components. Several of these issues originate from pressure pulsations and vibrations stemming from distinct regions of the turbine. Among these are the Rotor-Stator Interaction (RSI) and shedding frequency. There has previously been performed both pressure measurements and simulations throughout the Francis rig in the Waterpower Laboratory at NTNU. The area of interest in this thesis is the vaneless space, located between the guide vanes and turbine runner. The velocity field in the vaneless space was measured using Particle Image Velocimetry (PIV) equipment. There is currently no available research using PIV equipment in this section of a Francis turbine. Consequently, a major part of this thesis was designing a full equipment setup procedure, as well as a measurement campaign. The solutions used is showcased throughout this project paper. The velocity field was successfully measured for a range of guide vane openings, but due to time constraints the focus of this thesis is the Best Efficiency Point (BEP). For this operating condition the velocity field was compared to computational fluid dynamics simulations. Additionally, both RSI and shedding frequency was identified in the vaneless space. A clear relation between these fluid phenomena was not found for BEP conditions