Simulation of a Combined Nozzled and Nozzleless Twin-Entry Turbine for Improved Efficiency

This paper discusses the performance and the mass flow characteristics of a twin-entry turbocharger turbine with a fixed nozzle entry and a nozzleless entry for the automotive application. Because the configuration, which is based on a conventional twin-entry nozzleless turbine, has both a fixed nozzle entry and nozzleless entry simultaneously, and the fixed nozzle entry and the nozzleless entry have different rotor incidence angles, stratified flow is formed in the rotor inlet. The numerical simulation results show that the new turbine with double-rotor incidence angles has higher efficiency compared to the original twin-entry nozzleless turbine, especially in low-speed condition, which can greatly improve the low-speed torque of the engine. By investigating the installation locations of the fixed nozzle, it is more beneficial to improve the turbine efficiency when the fixed nozzle is set at the outer scroll near the turbine outlet. The influence of the vane installation angle on the turbine performances is studied in order to optimize the turbine structure and to find out the turbine performance characteristics. It shows that 60 deg is the optimal vane angle. This paper introduces the concept of the double-rotor incidence angles and the details of the configuration optimization.