Stability improvement in high pressure-ratio centrifugal impeller with self recirculation casing treatment

In order to explore the mechanism of stability improvement, numerical investigations are performed to examine the role of the self recirculation casing treatment and a recirculation device in which upstream slot is sealed in the enhancement of operational range of a centrifugal impeller with high pressure-ratio. The numerical results approve that self recirculation casing treatment not only can suspend the stall effectively but also can improve the impeller efficiency and total pressure ratio appreciably in the near of stall region. The detailed analysis of the flow field at the blade tip shows that it reduces the blade loading in the impeller tip region. And hence the velocity of tip leakage flow exiting the bleed slot becomes lower compared with that without the self recirculation device. All these effects induced by the recirculation device are considered to lead to the suppression of the extension of blockage and to contribute to the enhancement of the impeller operating range.