NUMERICAL ANALYSIS AND EXPERIMENTAL VERIFICATION OF INLET RECIRCULATION FOR UNSTABLE FLOW SUPPRESSION IN A CENTRIFUGAL BLOWER

摘要

A ring groove arrangement is proposed to suppress unstable flow in a centrifugal blower. The ring groove arrangement connects the impeller inlet upstream and the inducer throat tip, and forms an inlet recirculation through a bypass for the two regions. The inlet recirculation at small flow rates results in a decrease in the flow rate of unstable flow inception. An up to 8% improvement in surge margin was obtained by the ring groove arrangement at a small expense of the delivery pressure drop. A 3-D turbulent flow calculation was conducted to investigate effects of the inlet recirculation on the main through-flow and unstable flow suppression in the impeller. The calculated results were compared with the experimental ones. It is found that the critical flow incidence is about 7.4 degrees for separation bubble formation at the blade leading edge, and the surge suppression is mainly due to decrease in flow incidence at the impeller leading based on the inlet recirculation flow.