Preliminary simulation of Porjus U9 turbine at speed no load
Abstract: Hydropower plants are shifting towards operating at off-designed conditions, meaning that the number of start-stop cycles and maintenance time due to cavitation increases. The speed no-load condition is the moment before magnetization of the generator, i.e., no load, low flow, constant runner rotational speed, guide vane and runner blade angle. Since no load is applied, the water dissipates its energy in forms of highly recirculating and turbulent flow. This master thesis aim is to simulate the speed no-load condition on the Porjus U9 turbine and validate numerical values against experimental ones. ICEM CFD was used to mesh the domains and ANSYS CFX was used to perform the simulation. The setup was split into two zones, Zone 1 and Zone 2, and an intermediate zone overlapping both zones. Zone 1 consists of the penstock and spiral, the intermediate zone consists of the spiral and distributor passages and Zone 2 consists of a distributor passage, runner and draft tube. Streamlines in the runner and draft tube show highly recirculating flow from the draft tube back into the runner. The numerical values did not correspond well against the experimental. This is deemed most likely due to an overall low pressure over the runner blades. It is recommended as a first step to increase the quality of the runner and distributor mesh to get the simulation running with the cavitation model implemented.
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