Secondary flow phenomena in diagonal flow impellers

The measurements of flow fields have been performed by changing tip clearance and flow rate for two diagonal flow impellers with different vortex types, a free vortex type and a vortex type of constant tangential velocity. This paper presents overall behaviors of the secondary flow in the diagonal flow impellers to offer available data for modeling of spanwise mixing due to the secondary flow. The characteristics of the secondary flow are that, in comparison with axial flow impellers, the leakage vortex roll-ups are not seen clearly and the low energy region caused by the tip leakage flow is larger. As the tip clearance increases, the low energy region near the casing becomes larger and shifts toward the suction side of the blade. The low energy region tends to move from the pressure side to the suction side with decrease of the flow rate. For the impeller with a vortex type of constant tangential velocity, there exists a strong secondary flow due to the spanwise loading distribution.