This thesis presents a numerical calculation of the characteristic of a small unregulated axial water turbine using computational fluid dynamics in the Ansys CFX software environment. An already created geometry and structured numerical mesh were used. The SST and SAS-SST models were used for turbulence modelling, while three methods were used to model the interaction between the rotating and stationary domain: frozen rotor, mixing plane, and transient rotor-stator. The turbine characteristic was calculated over a range of average inlet velocities from 0.8 m/s to 2.4 m/s using steady-state and transient calculations, with the transient calculations serving as a reference. It was found that the relative deviation of the torque and pressure drop calculated with the steady-state methods decreases with increasing flow rate, with the deviation in torque on the runner amounting to 80% at the lowest flow rate and less than 2% at the highest. In the flow analysis using the SAS-SST turbulence model, the resolution of turbulent structures was observed in the region behind the runner, similar to the LES model, which led to more accurate results at the lowest flow rate compared to using the standard SST model.
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