Forced and natural aeration for pressure fluctuation mitigation in a 250 MW Francis turbine: prototype-scale experimental assessment
摘要
Hydraulic instabilities within Francis turbines during part‑load operation are often responsible for the development of draft‑tube vortex ropes, severe pressure pulsations, and cavitation events, narrowing down the operational flexibility. Despite recent research in the laboratory on using aeration as one mitigation method, limited prototype‑scale evidence exists to quantify the comparative effects of natural and forced aeration on pulsation attenuation. This paper fills this knowledge gap by providing an experimental study on a prototype Francis turbine to investigate how dual‑mode aeration affects the dynamic pressure field and vortex‑rope suppression. A custom designed under runner aeration structure allowed for both natural suction and controlled forced air injection, and thus enabled systematic testing for three operating conditions: (i) non‑aerated, (ii) natural aeration, and (iii) forced aeration. Pressure pulsations were monitored along the penstock and draft tube for head of 147 m using synchronized high frequency sensors. Results show that aeration strongly reduces pressure fluctuations (peak relative pulsation amplitude