Numerical simulations of the pressure time method in a full-scale turbine
Abstract: Efficiency measurements are an important part of operating and maintaining a hydroelectric turbine. In order to calculate the efficiency, one need a method to accurately measure the flow rate. The pressure time method is a way to calculate the flow rate from pressure measurements, which are done during a transient. This master thesis aims to evaluate the possibility to implement the pressure time method in prototype turbine with variable intake cross-section. To this end, numerical simulations of the method on a prototype situated in Porjus were performed. The work was compared against experimental data obtained on the machine. Three operating points were evaluated, and two different numerical simulations were done for every operating point, with and without guide vanes. For the simulation without guide vanes, the deacceleration stems from the control of the flow at the outlet. The curve for the mass flow at the outlet was calculated with the pressure time method with data from the experiments. For the simulation with guide vanes the deacceleration stems from the guide vanes closing. The results from the simulations gives a reasonable fit to the experimental data. There is a difference between the simulations with and without guide vanes, though both are on the same magnitude. The largest differences between the simulations and experimental data is theorized to be due to either the assumption of an axisymmetric flow or the outlet boundary conditions.
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