Effects of variable vaned diffuser on compressor performance and aerodynamic noise in a marine diesel engine turbocharger

Abstract

The variable vaned diffuser has been used to widen the operating range of turbocharger compressors under high-pressure-ratio conditions. The effects of variable vaned diffusers on compressor performance and aerodynamic noise are investigated with the numerical approach in this paper. First, the numerical approach is validated using the compressor with a fixed diffuser. Then, a variable diffuser features three rotating centers, each with a distinct rotation angle. Finally, the aerodynamic performance, fluctuation pressure characteristics, and aerodynamic noise of the compressor with variable vaned diffuser are analyzed. The results indicate that the use of a variable vaned diffuser shifts compressor operating range toward lower flow rates with positive rotation angles, while negative rotation angles shift the operating range toward higher flow rates. The diffuser can effectively expand the compressor’s operating range within a rotation angle range of 0°–5° without significantly affecting its pressure ratio and efficiency. Compared to the rotation angle, the movement of the rotation center from the leading edge to the trailing edge has a relatively small impact on the compressor’s performance. Additionally, the rotation center affects the compressor’s noise, likely due to changes in the diffuser inlet and outlet radii caused by the rotation center, which influence the dynamic-static interference between the diffuser, volute, and impeller. Although the variation in the rotation center interferes with the results of the rotation angle’s effect on the compressor’s aerodynamic noise, a general trend can still be derived. Specifically, the variable-rotation angle diffuser with positive rotation angles increases the compressor’s sound pressure level (SPL), while negative rotation angles generally reduce the compressor’s noise. This is because the diffuser with positive rotation angles increases fluctuating pressures in the inlet duct, impeller passage, and diffuser passage, while negative rotation angles reduce fluctuating pressures in the inlet duct and impeller passage.