Three-Dimensional Investigation of Flow in Centrifugal Impeller with Straight-Radial Blades

The flow through the passage of rotating impellers with single and double shrouds (full shrouds) has been studied experimentally by means of a test rig, so designed that it is possible to measure directly the relative velocity, flow direction, total and static pressure on several points in the passage while the impeller is rotating. On the other hand, the theoretical analysis was made under the assumption of two-dimensional potential flow, and the calculated results are compared with the measured results in terms of relative velocity under the given operating conditions. The velocity distribution and the flow direction obtained in the experiments indicate that secondary flows in the boundary layer tend to shift the low-energy air toward the negative surface (Suction surface) of the blade in the passage. In case of single shrouded impeller, there is observed a counter effect along the casing surface apparently caused by the leakage through the clearance space between the blade and the casing. This results in a voltex flow in the passage. It can be concluded that the secondary flows consequently dominate the flow condition, and make it so complicated that it is impossible for us to conjecture it by means of theory.