An experimental study of the unsteady characteristics of tip-leakage flow of axial fans with circumferential skewed blades at off-design conditions

The unsteady characteristics of tip-leakage flow in axial fans with circumferential skewed blades were investigated at off-design conditions using particle image velocimetry (PIV) and wall pressure test. Two circumferential skewed fans, with the blade skew angles at 8.3° forward and backward, respectively, were investigated in this study. The instantaneous flow field in tip clearance region was measured using PIV at peak pressure condition. The static pressure fluctuations near blade tip were captured at off-design conditions using pressure sensors mounted on casing wall. From the measured results, the structure and instantaneous characteristics of tip-leakage flow in circumferential skewed fans were analysed. The tip-leakage vortex instability and its relation with circumferential skewed blades, to expand stall-free operation range of axial fans, were discussed. The forward-skewed blade is found to be effective in controlling tip-leakage flow to expand stall-free operation range at off-design conditions.