THE EFFECTS OF RADIALLY DISTORTED INCIDENT FLOW ON THE PERFORMANCE OF AXIAL-FLOW FANS WITH FORWARD-SKEWED BLADES

In this study, the experiments and simulations have been carried out to evaluate the effects of radially distorted incident flow on the performance of axial-flow fans equipped with forward-skewed blades. These fans were manufactured with different forward-skewed angle, such as 3 degrees, 6 degrees and 12 degrees respectively. Based on the experimental and numerical results, it is found that under the uniform inlet condition the fan with the 12 degrees forward-skewed angle manifests the most excellent performance, and its peak efficiency is increased by 6.27% and 3.41% respectively in comparison with those of two other fans. However, when a hub-covered screen is mounted and then the uniform inlet condition is consequently destroyed, the peak efficiency of all three fans is decreased by more than 2.8%. Under the third inlet condition, as the main stream is compelled towards blade hub by a tip-covered screen, the effect of forward-skewed blades on the fan performance is reinforced and fan performance is improved. In order to get further understanding, contours of the loss coefficient and the axial velocity at exit have also been studied both at the design point and the lower mass rate point. All results exhibit that there are beneficial effects of forward-skewed blades on fan performance and the performance is quite sensitive to radially distorted incident flow. Furthermore, rotating stall has been observed by use of three dynamic pressure sensors. The instantaneous results reveal that when the fans are operated with different kinds of incident flow, pressure fluctuations with time have different modes as the fans are sliding down into rotating stall.