The introduction of intermittent renewable energy sources, such as wind and solar power, to the power grid, demands some hydraulic turbines to operate at unfavorable operating conditions not initially designed for. Strong swirl develops at loads below the best efficiency point, (BEP) due to angle mismatch between the guide vanes and the fixed runner blades typical for Francis and Propeller turbines. A rotating vortex rope (RVR) is developed at part load (PL) operation as a consequence of the strong swirl exiting the runner for the aforementioned turbines. The RVR is associated with harmful pressure pulsations, decreasing turbine efficiency, and increasing maintenance time. Thus, it is of great interest to develop and investigate methods to mitigate the RVR. Methods to mitigate the adverse effect associated with the RVR at PL are studied in the presented research. An active mitigation method was numerically studied for a down-scaled propeller turbine, named "injection of pulsating momentum" (IPM). IPM aimed to locally disrupt the RVR by injecting pulsating momentum horizontally into a local part of the quasi-stagnant region in the draft tube. Numerical results indicate a significant reduction of the pressure pulsations associated with the RVR using approximately 5% of the runner flow. A passive mitigation method was also studied on a numerical model of the Porjus U9 Prototype using stationary rods radially protruded into the draft tube flow field. Solid rod protrusion aims to alter the mean flow properties in the draft tube cone, disrupting the formation of the RVR. Numerical results of stationary rod protruding to the RVR shear layer region indicates a complete reduction of the RVR plunging component and a significant reduction of the RVR rotating component due to an increased swirl at the draft tube center.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:ltu-89952 |
| Date | January 2022 |
| Creators | Holmström, Henrik |
| Publisher | Luleå tekniska universitet, Strömningslära och experimentell mekanik, Luleå |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Licentiate thesis, comprehensive summary, info:eu-repo/semantics/masterThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | Licentiate thesis / Luleå University of Technology, 1402-1757 |
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