CFD simulation of wind turbine rotor aerodynamics and droplet impingement on blades
Välimäki, Valtteri (2023)
Välimäki, Valtteri
2023
Ympäristö- ja energiatekniikan DI-ohjelma - Programme in Environmental and Energy Engineering
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Hyväksymispäivämäärä
2023-01-27
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202301111333
https://urn.fi/URN:NBN:fi:tuni-202301111333
Tiivistelmä
In a transition to more sustainable energy production, wind power has been playing a growing role. It is appealing to build wind farms in the offshore, where there are good wind conditions. The trend is to build turbines with larger swept areas to maximize the power output of one turbine. With longer blades, the blade tip speeds increase as well as the impact speeds of impurities in the air. These impurities can start to erode the blade. Wind turbine leading edge erosion is a significant problem since it affects the aerodynamics of the wing and therefore it has impact on the energy produced. Erosion of the blades also increases the maintenance costs, which can be especially high in the offshore conditions. In this thesis work a water droplet impingement on wind turbine blades is investigated with CFD (Computational Fluid Dynamics) simulations. The main goal is to study droplet trajectories and impact speeds on a wind turbine blade in 2D and 3D simulations and to produce impingement data which can be used in a wind turbine erosion model developed in VTT research center in Finland. The goal is to investigate the differences between 2D and 3D droplet simulations. All the simulations are done with ANSYS Fluent software using a steady state solver.
To ensure the accuracy of the droplet calculations, air flow simulations in 2D and 3D are validated. This is done by comparing simulated results for forces and moments acting on a blade to existing wind tunnel data. The simulation models used in the validation cases are selected based on the models used in similar studies found in literature. After the validation of the simulation results, the droplet trajectories are calculated in the postprocessing of a converged flow solution of 15 MW IEA (International Energy Agency) reference wind turbine (RWT). Droplets are released in the flow field by injections using DPM (Discrete Phase) model.
From the validation cases it can be concluded that the forces and moments can quite accurately be simulated with CFD tools. However, the simulation results compare well with the experimental result only when there is no excessive flow separation from the wing. In the 3D validation cases the simulated torque values of NREL (National Renewable Energy Laboratory) phase VI rotor were in very good agreements with the experimental results with the wind speeds of 7 m/s and 10 m/s with the error percentage of around 5 %. With the wind speeds of 13 m/s and 15 m/s the difference increased to around 25 % due to flow separation. By comparing the impact speeds and trajectories of different sized droplets it can be concluded that the trajectories of bigger droplets behave more like a straight line whereas smaller droplets are adapted by the surrounding flow nearly instantly. The difference between in 2D and 3D simulations was that the impact speeds of droplets were lower in 3D simulation than in 2D simulation. The difference was emphasized with smaller droplets. For future work, the reasons behind the different impact speeds in 2D and 3D simulations could be studied. Also, different particle diameters and densities could be investigated.
To ensure the accuracy of the droplet calculations, air flow simulations in 2D and 3D are validated. This is done by comparing simulated results for forces and moments acting on a blade to existing wind tunnel data. The simulation models used in the validation cases are selected based on the models used in similar studies found in literature. After the validation of the simulation results, the droplet trajectories are calculated in the postprocessing of a converged flow solution of 15 MW IEA (International Energy Agency) reference wind turbine (RWT). Droplets are released in the flow field by injections using DPM (Discrete Phase) model.
From the validation cases it can be concluded that the forces and moments can quite accurately be simulated with CFD tools. However, the simulation results compare well with the experimental result only when there is no excessive flow separation from the wing. In the 3D validation cases the simulated torque values of NREL (National Renewable Energy Laboratory) phase VI rotor were in very good agreements with the experimental results with the wind speeds of 7 m/s and 10 m/s with the error percentage of around 5 %. With the wind speeds of 13 m/s and 15 m/s the difference increased to around 25 % due to flow separation. By comparing the impact speeds and trajectories of different sized droplets it can be concluded that the trajectories of bigger droplets behave more like a straight line whereas smaller droplets are adapted by the surrounding flow nearly instantly. The difference between in 2D and 3D simulations was that the impact speeds of droplets were lower in 3D simulation than in 2D simulation. The difference was emphasized with smaller droplets. For future work, the reasons behind the different impact speeds in 2D and 3D simulations could be studied. Also, different particle diameters and densities could be investigated.