Investigation of clearance flows in deeply scalloped radial turbines

The tip clearance, backface clearance, and backface cavity clearance flows in deeply scalloped radial turbines are numerically investigated in this article. The secondary flow structures in the rotor passage with the three clearance flows are shown and their influences on the distribution of aerodynamic parameters at the rotor outlet are analyzed. It is found that the migration of the tip clearance flow is constrained near the tip corner, and the region influenced by the tip clearance flow is mainly located at the upper span. With the largest mass flow rate, the tip clearance flow has the greatest impact on the outlet parameters among the three clearance flows. The backface clearance flow enters the mainstream from the blade backface and migrates toward the blade tip due to the centrifugal force. And it mainly affects the distribution of outlet parameters at the mid-span. The backface cavity clearance flow is injected into the mainstream from the disc rim. It moves toward the blade tip and stays close to the suction surface. With the smallest mass flow rate, the impact of the backface cavity clearance flow on the outlet parameters is the lowest.