Internal flow characteristics of a variable mixed flow turbine with partially-rotating vane nozzle

Variable nozzle turbine has advantages of improving engine low-speed performance; thus, it is widely applied in internal combustion engines. The present study analyzed the aerodynamic performance, especially the nozzle endwall leakage flow loss of a mixed flow turbine with variable nozzle, using 3D computational fluid dynamic simulation and test validation. Then, a partially-rotating vane nozzle was proposed to reduce the nozzle endwall clearance leakage flow to improve turbine efficiency. The results showed that at small nozzle opening condition, the front-part-vane rotating design can improve turbine efficiency up to 5.95 %, and the efficiency improvement of the rear-part-vane rotating design is approximately 5.08 %. At large nozzle opening condition, the front-part-vane rotating design has the same efficiency and flow capacity as the origin design, but the rear-part-vane rotating design cannot satisfy the flow capacity requirement. Detailed flow field analysis shows that the front-part-vane rotating design affects the velocity distribution at the rotor inlet due to nozzle endwall leakage flow. The leakage flow between the front part and the rear part of the nozzle causes a pressure jump at the pivoting axis.