A new method of drilling through-holes near the blade suction surfaces in the shroud of a centrifugal impeller is proposed

where pressurized air in the volute casing generates jet flows to directly supply additional energy to the flow characterized by low velocity or separation inside the impeller. Consequently the jet-wake flow caused by secondary flows in the impeller is weakened

and the often encountered problem of dust or ash accumulated on the blades under partial loads is expected to be solved to some extent. The computational results show that the total pressure rise of the fan with holes in the shroud increases by 2% and efficiency over 1% at designed flow rate while the increase in the total pressure rise reaches to 1.5% and efficiency 2.1% at lower flow rate. Furthermore

the change of the internal flow fields indicates that the separated flows at the exit of the impeller are improved obviously due to the jet flows through the holes at designed and lower flow rates. In addition

the area with low velocity and the peak values of the radial velocity as well as the radial velocity gradient are also reduced reasonably

which leads to weakened jet-wake flows at the exit of the impeller. Along the blades the separation regions become smaller and the increases in the static pressure become more regular. As a result

better performance of the shrouded impeller and of the fan can be achieved by drilling through-holes in the shroud

and this new method can be used in combination with other adaptive boundary control technique in the centrifugal impeller to totally improve the performance of the fan.