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Endoscopic Stereoscopic PIV Measurements Within An Enclosed And Tight Area Of A Hydraulic Turbine

Araz Rezavand Hesari, Anthony Munoz, Maxime Coulaud, Sébastien Houde, Yvan Maciel

Heki, Université Laval, Québec, Canada


The increasingly common utilization of hydraulic turbines in off design operating conditions in recent years have affected their lifetime due to damaging fluid-structure interactions. To decrease the downtime associated to more frequent maintenance of these turbines, a thorough understanding of the damaging flow phenomena is required. This may eventually lead to the development of mitigation strategies. However, measuring velocity at the entrance of the rotor of Francis turbines is difficult because of the confined spaces and limited optical access. This paper presents a stereoscopic PIV methodology enabling measurements at the inlet of a reduced-scale Francis turbine, along with multiple novelties developed to make accurate measurements possible. It elaborates on the solutions devised to address the challenges of performing optical measurements in highly confined spaces. The measured velocity fields cover the vaneless space and a large section of the interblade channels. In the phase-averaged velocity fields, three circulation zones are detected at the speed-no load operating point, representing the combined effect of numerous vortices and flow structures observed in the instantaneous velocity fields. The flow is characterized by a significant backflow within the runner, extending to the leading edge of the runner blades and overflowing into the vaneless space.

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