Laser-based Measurements connected to Fish Migration

Sammanfattning: Hydropower is one of the main sources for Sweden’s energy, which is clean and renewable. It is a clean energy source because no fuels are burned which does not pollute the air and it is a renewable energy source as it only uses natural water cycle for generating energy. However, hydropower has some consequences in nature, such as creating dams in rivers and changing water flow directions, which lead to some problems for migrating fishes. These fish migration problems are mostly studied from a biological point of view but more detailed studies are required from a fundamental fluid mechanics point of view. Fish migrates when ecological imbalance is created and one of the reasons for this imbalance is having dams for hydropower. Some dams have fishways or fish ladders to allow fish to migrate past the dam and during swimming or passing this fishway or fish ladder, fish has to tackle some sort of flow obstructions like, turbine intakes, stones and concrete structures etc. Fluid flow characteristics in fish ladders or fishways during fish migration is crucial for designing effective fishways to migrate fishes effectively. Flow characteristic measurements can provide quantitative information of the velocity distribution in fish ladders, which has strong correlation with the attraction of of fish. Recent research suggests that turbulence also has a large effect on fish migration. This is why obtaining flow information from well-defined turbulent flows, such as flow past cylindrical objects is the prime aim of these measurements.Particle Image Velocimetry (PIV) and Laser Doppler Velocimetry (LDV) have become the most popular and promising techniques for these types of non-contact measurements. PIV techniques are used to visualize and measure the flow characteristic in a selected area while LDV techniques are suited for point-based measurement. The works included in this thesis are reviewing PIV techniques previously used in fish movement related studies, LDV measurements both at upstream (bow wake) and downstream wake of cylindrical obstructions and finally Computational Fluid Dynamics (CFD) for validation of experimental measurements. The results find relatively acceptable agreement between CFD and experiments with some disparities.