A tip-leakage loss reduction method using a front-loaded blade profile for the high-pressure rotor of a vaneless counter-rotating turbine

To reduce tip-leakage losses, this paper presents a front-loaded blade profile design method for the high-pressure (HP) rotor of a highly loaded vaneless counter-rotating turbine (VCRT). The method is to decrease the blade exit angle and increase the stagger angle with unchanged throat area to obtain front-loaded blade profiles at both the tip-leakage vortex upper and lower boundaries. As the relative exit Mach numbers in the tip region of the VCRT's HP rotor are all over 1.5, the shearing of the high-speed leakage jet and passage flow near the trailing edge is very strong. To reduce the shearing losses, decreasing the blade exit angle of the HP rotor is adopted to reduce the tip loading near the trailing edge. This means the leakage jet mass-flow rate and speed near the trailing edge are reduced. Hence, the shearing strength and losses of the leakage jet and passage flow near the trailing edge are lower. Since decreasing the blade exit angle of the HP rotor results in increased throat area, increasing the stagger angle is employed to maintain unchanged throat area. Increasing the stagger angle also reduces the tip loading near the trailing edge, leading to reduced high-speed leakage jet mass-flow rate. Thus, the shearing strength and losses of the high-speed leakage jet and passage flow near the trailing edge are further reduced. The efficiency of the HP rotor and VCRT are raised by 0.45% and 0.53% respectively.