Suppression of inducer stall based on inlet recirculation in a centrifugal impeller (2nd report, numerical analysis of stall suppression effect)

The ring groove arrangement was proposed to improve surge margin in a centrifugal blower. The inlet recirculation formed by the arrangement at small flow rates resulted in a significant decrease in the flow rate of the unstable flow inception at a small expense of the delivery pressure drop. The effect of inlet recirculation on the main through-flow in the impeller and the unstable flow suppression is analyzed by the 3-D turbulent flow calculation, and the calculated results are compared with the experimental ones. The critical flow incidence is about 7 degrees for the separation bubble formation at the blade-leading edge. In the tested impeller, the separation bubble on the blade suction surface extends along the blade leading edge from the blade root to a radial position of the root-mean-square radius at the stall limit flow rate. It is found that the surge suppression is mainly due to decrease in flow incidence at the blade-leading based on the inlet recirculation flow.