A casing treatment is one of the efficient devices for suppression of unstable flow at small flow rates in axial compressors and blowers, but not always common in centrifugal compressors, ft was verified experimentally as well as numerically by the authors that the implementation of an inlet ring groove arrangement was fairly efficient for suppression of unstable flow occurring at small flow rates in a centrifugal impeller integrated with inducer. According to the authors previous study based on the numerical simulation, the recirculation flow is formed from the ring groove located near the inducer tip throat to the blower inlet through the annular bypass, and both the tip leakage flow and the reverse flow near the inducer tip are sucked into the ring groove, resulting in the unstable flow suppression. In this case, a large-positive flow incidence is reduced successfully due to not only the increased incoming flow rate but also the pre-whirl induced by the recirculation flow.
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