On the pressure losses due to the tipclearance of centrifugal blowers

The pressure distribution along the shroud is measured for three types of centrifugal impeller at seven different values of tip clearance each.The change of input power due to a change of tip clearance is related to theeffective blockage at the impeller tip. Since the change of input power is little for the test cases, the variation of local pressure gradient along theshroud is mostly attributed to the change of local pressure loss. The local pressure loss is related to the local tip clearance ratio and to the local pressure gradient based on the deceleration of relative velocity in the impeller. Since the local pressure gradient is largest near the throat of the impeller, for many impellers the clearance ratio at the throat is used as the representative value. The tip clearance loss is related to the clearance ratio and the pressure rise based on the deceleration of relative velocity in the impeller. A good correlation is observed in all cases at various flow rate.