Stall Margin Improvement of an Axial Flow Fan with End Wall Injection and Suction. 2nd Report. A Study of Stall Recovery Margin Improvement.

Abstract

This paper presents the experimental results of stall recovery margin improvements. Studies have been conducted on a low speed axial flow fan to investigate the stall cessation flow rate with several kinds of injection or suction holes on the end wall. First of all, the fan characteristics for the solid wall have been measured. The hysteresis loop has been observed, but the size of hysteresis loop was not large, so that the stall cessation flow rate was about 17% smaller than the stall onset flow rate for several rotor speeds. Stall recovery margin improvements for both injection and suction were about 3 to 5% larger than stall margin improvements. For the case of injection, the position of maximum stall recovery margin improvements has moved to downstream direction a little from the position of maximum stall margin improvements. For the case of suction, the largest improvement was found at the position of just upstream of leading edge of blade. And negative improvement was not found except very large suction. For the case of injection, comparing with stall recovery margin improvements and stall margin improvements, both values are almost the same with regard to the injection momentum relative to the chordwise.