Mean Velocity Characteristics behind a Forward-Swept Axial-Flow Fan

Detailed measurements in the flow behind a highly forward-swept axial-flow fan at three operating conditions were performed using three-dimensional LDV system. Various phenomena related to the leakage flow, leakage vortex, hub vortex and wake were investigated. At the design condition, where no distinct leakage vortex appears behind trailing edge, the leakage flow interacts with the boundary layer of the pressure side inside the blade passage, which directly influence the wake characteristics behind the trailing edge. At the low loading condition, the leakage vortex has the characteristics of the velocity defect and this vortex induces radially inward flows at both the suction and pressure sides in the wake near the tip region. As the loading increases, radially-outward velocity component increases and the position of the maximum value in the wake is closer to the tip region. At the design and high loading condition, hub vortex induces radially inward flow at the pressure side and wakes near the hub region decays very quickly due to the interaction with the large hub vortex.