Design and analysis of a nozzle-less twin-entry turbine volute for automobile application

Abstract

Due to the increasing demand for improved fuel economy in passenger cars, recent internal combustion engines come with a turbocharger. Turbochargers are a method of engine downsizing that forces more compressed air into the combustion chamber, enabling a high power density. Two main types of turbines are commonly adopted in turbochargers; single-entry and multiple-entry. The multiple-entry type includes twin-entry and double-entry volutes. A twin-entry volute consists of two inlets with a divider that feed the entire circumference of a rotor whereas a double-entry volute has two separate inlets that feed the rotor separately. A twin-entry volute's design is based on a single-entry volute by merely placing a divider into the volute. The conventional design approach of a twin-entry volute gives relatively little consideration to the design aspects such as the divider's length, the divider's width, and the cross-sectional shape of the volute. The above-mentioned design aspects of a twin-entry volute have an impact on the performance of a turbine. This paper intends to design a new twin-entry volute with a specified divider length and width. The volute's profile is based on a single-entry volute. In addition, the performance of this twin-entry turbine is compared with the asymmetric double-entry turbine. The comparison of these configurations relies on consistent criteria, including the A/R ratio, mixed-flow rotor, and cross-sectional of the volute. The simulation was executed at two different turbine speeds; 30k RPM (50 %) and 48k RPM (80 %). The validation simulation shows great agreement with the experimental data with a Root Mean Square Error of less than 5 % for both speed lines. Based on the results obtained, the twin-entry turbine shows a lower swallowing capacity than the asymmetric double-entry turbine at both operating conditions. At both speed lines, the twin-entry turbine's efficiency begins to fall toward the end. The incidence angle of the twin-entry turbine is 24.4° at 50 % operating speed and -3.72° at 80 % operating speed. In both turbines, entropy generation reduces as the speed line increases, and both turbines exhibit a similar entropy generation at both speed lines. The existence of a horseshoe vortex near the hub surface and the tip leakage vortex near the shroud region of the blade substantially influence both the turbines' performance.