Abstract
Two kinds of passive control devices are successfully combined for suppression of unstable flow at small flow rates in a centrifugal blower. The one is the inlet ring groove arrangement and the other is the low solidity cascade diffuser. By applying the inlet ring groove arrangement, the tip leakage flow and the reverse flow in the inducer is sucked through the ring groove located near the inducer tip throat, and the flow incidence was effectively reduced. The pressure rise at the impeller exit was successfully improved by the ring groove arrangement, but the pressure rise in the vaneless diffuser was decreased. The CFD analysis showed that the tangential component of absolute velocity at the impeller exit was decreased. Then, the decreased centrifugal force must be a main reason why the pressure rise in the diffuser became small. By applying the low solidity cascade diffuser as well as the ring groove arrangement, the blower pressure rise was improved around 6%, however, the surge margin was deteriorated a little.
