The velocity profiles, radial and circumferential components, were measured at the tip of a forward curved centrifugal fan. Three sets of measurements are presented. Two at peak efficiency for different rotational speeds and a third at the lower rotational speed and for a reduced flow rate.
A reverse flow region was formed near the hub, and almost in the middle, between pressure and suction sides of the blade. Near the shroud a high velocity region was observed and a low one near the suction side, picture similar to the jet-wake structure found in the literature.
At the lower rotational speed and low flow rate the flow was affected mainly by the system rotation. A “wake” was formed along the suction side of the blade. Increasing the flow rate blade curvature effects became more dominant.
Increasing the rotational speed and for the same flow coefficient the system of two vortices observed in the previous case disappears and a single vortex takes its place. In this case the wake is positioned on the hub.
Corner vortices also affect the main flow by changing the turbulence intensities. A corner vortex observed on the pressure side reduced the turbulence intensities in the region and a wake was formed locally. However, another corner vortex on the suction side caused an increase to the local turbulence intensities and consequently a high local velocity.