Generic Properties of Flows in Low-Speed Axial Fans Operating at Load-Controlled Windmill.

This paper aims at underlining the existence of some generic properties of windmilling flows, partially spread in the literature but never clearly stated. Two kinds of axial machines are investigated from compressor mode to highly loaded windmill: a conventional fan with poor turbine performance and an optimized fan able to reach high efficiencies in both compressor and windmilling operations. Both simulations and experiments are used to perform the analysis. Three particular behaviors were identified as typical of fans operating at windmill: the inverse stacking of the speed lines visible in (π, Q_m^-) turbine maps, the appearance of a slope change on the loading-to-flow coefficient diagram at windmill, and a threshold effect occurring at highly loaded windmill. [ABSTRACT FROM AUTHOR]