14th European Conference on Turbomachinery Fluid dynamics & Thermodynamics
Low-speed fans for automotive cooling systems are large-scale products that have peculiar geometries dictated by their particular installation. A typical feature is the rotating shroud, i.e., a ring connecting the blade tips. Furthermore, due to absence of a cylindrical shroud upstream of the rotor, the incoming fluid typically flows on a flat surface with a 90-degrees turn from radial to axial. This may yield a complicated interaction between the two flows which affects both performance and radiated noise. The pressure rise strongly influences such an interaction, since the pressure rise has opposite effects on the main flow rate and on the leakage one. In a previous paper, ETC 2019-368, the same authors showed that different kinds of flow separation may yield, both upstream of the rotor and on the rotating shroud. However, that paper mainly focussed on the noise generation and a limited number of operating point were surveyed. In the present work, the flow in the gap region has been studied by means of 2D PIV measurements taken in the meridional plane at 12 different static pressure rise values. At free-discharge conditions, the flow smoothly turns from radial to axial. As the pressure rise increases, a small separation bubble forms close to the gap whose size increase and, at a certain value of the pressure rise, the jet leaving the gap penetrates the main flow, resulting in a centrifugal flow. At larger pressure rise values, a separation bubble forms on the ring, which may lead the blade tip region to stall.