This experimental study determined the degradation in performance of large axial fans caused by close inlet walls. Three fans with hub to tip ratios of 0.39, 0.49, and 0.74 were each tested at four blade angles and over the flow rate range of wide open to near shutoff. The closest walls, 0.5D front clearance and 0D side clearance, caused only modest loss in flow rate, up to 3½%, and less than a 5% loss of efficiency in the 0.49 H/T fan. The other two fans had only minor decreases in flow rate and in efficiency for the closest walls. No significant losses were found for any of the test fans when tested with clearances larger than the minimum.

Units: Dual