A three-dimensional unsteady flow separation in the straight diffuser of a model bulb turbine is investigated using tuft visualizations, unsteady wall pressure sensors, and particle image velocimetry (PIV). Experimental results reveal a link between the flow separation zone extension and the sudden drop in turbine performances. The flow separation zone grows as the flow rate increases past the best efficiency operating point (OP). It starts on the bottom wall and expands azimuthally and upstream. It deviates and perturbs the flow far upstream. Despite high unsteadiness, a global separation streamline pattern composed of a saddle point and a convergence line emerges.
Investigation of Flow Separation in a Diffuser of a Bulb Turbine
Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received September 9, 2014; final manuscript received July 7, 2015; published online September 3, 2015. Assoc. Editor: Bart van Esch.
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Duquesne, P., Maciel, Y., and Deschênes, C. (September 3, 2015). "Investigation of Flow Separation in a Diffuser of a Bulb Turbine." ASME. J. Fluids Eng. January 2016; 138(1): 011102. https://doi.org/10.1115/1.4031254
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