Research on unsteady flow characteristics of turbocharger turbine stage with coupling inlet and exhaust casings

The inlet and exhaust casings of marine turbochargers are closely coupled to the axial flow turbine. These are crucial parts that work with the axial flow turbine and have the ability to raise the power plant’s output power even higher. Their final stage of the axial flow turbine and the exhaust casing’s complex flow due to their close relationship will have a significant effect on each other’s aerodynamic performance. However, most existing studies have not paid sufficient attention to this coupled transient interaction. In this paper, the flow interaction between the axial flow turbine and the inlet and exhaust casings is studied. Particular attention is paid to the study of the coupled flow characteristics under design and variable operating conditions. This study is carried out using coupled computational fluid dynamics (CFD) simulation. The computational domain consists of an inlet casing, 28 stator blades, 43 rotor blades, and an exhaust casing. The commercial CFD software ANSYS CFX solver and the SST turbulence model are used to simulate the unsteady flow field of the turbocharger axial turbine coupled to the inlet and exhaust casings. In this paper, the turbine flow field and the inlet and exhaust casings flow fields are analyzed, and the influence of the exhaust casing on rotor surface pressure fluctuation is discussed. In addition, the flow field distribution and performance parameters of the axial flow turbine coupled with the inlet and exhaust casings under three different operating conditions have been calculated and analyzed. The results show that the inlet casing affects the circumferential distribution of the stator leading edge pressure, while the asymmetric back pressure caused by the exhaust casing flow field causes the low-frequency pressure fluctuation at the rotor blade surface. At the trailing edge of the suction surface, the complex flow separation and vortex structure in the exhaust casing are the main factors causing rotor-stator interaction. The low-frequency fluctuation amplitude caused by the exhaust casing is greater than that caused by the high-frequency fluctuation of the rotor-stator interaction. Moreover, as the flow coefficient increases, the low-frequency fluctuation amplitude is much greater than the high-frequency fluctuation amplitude.