Ventilatore centrifugo : Effetto de gioco all'apice della pala

A detailed flow field investigation was performed in an unshrouded centrifugal fan model by means of LDV and pressure measurements. The purpose of this work is to understand the development and the evolution of the separated and secondary flows along the whole blade channel with detailed spanwise and pitchwise velocity profiles for different tip clearances (5%, 12.5 %, 37.5 %, 100% of the blade height). Different clearances cause, at channel rotor outlet, different jet&wake flows with different extension and intensity. In the clearance region a weak backflow is present. At the maximum tip clearance the wake is quite negligible and a spanwise non-uniform flow field is present: this is the main difference on the flow field caused by different tip clearance. Maps of secondary flows show the presence of strong vortices at rotor inlet and outlet due to the tangential component of the backflow. The wake generates strong secondary flows which depend on the radial position inside the rotor. A strong dependence of the slip factor from tip clearance width has been also shown.