CFD Analysis Of The Twin-Screw Supercharger

According to China’s urban transportation speed, often in low-speed range, long idle time, and engine condition alternate frequently, twin-screw supercharger has a huge market potential because of excellent low speed torque characteristics and good transient response. Foreign twin-screw supercharger manufacturers have mature models and R&D means. The domestic twin-screw superchargers are in its beginning, which basically rely on the introduction of foreign models for simple processing and assembling. Thus independent analysis of the twin-screw supercharger has practical significance.Return shocks, exhaust pressure pulsation, leak and flow loss and other issues, which seriously affect the performance of the twin-screw supercharger. It’s hard to obtain the flow details of twin-screw supercharger through theory and test. CFD research method is a good way to obtain the twin-screw supercharger’s flow characteristics. This paper obtains the flow characteristics by the three-dimensional unsteady numerical simulation analysis.This paper simulates twin-screw supercharger’s unsteady multi-conditions through eight mesh models and dynamic mesh models. Command file makes the simulation efficient. Analysis results show the overall distribution of twin-screw supercharger is regular. Through the introduction of the concept of un-homogeneity and the analysis of the discharge pressure pulse curves, the discharge pressure has the same rotor angle as cycle at the different speed and pressure ratio, and the rotor speed is higher, the higher the pulse frequency. Eddy which resulted from the gas leakage has a direct impact on the intensity of the exhaust pressure pulsation. Pressure ratio and rotor speed has an important influence on the exhaust pressure pulsation.The gap is a prerequisite for safe operation of the twin-screw supercharger, but also the important factors that affect the the turbocharger volumetric efficiency and adiabatic efficiency. The gas leakage through the gap under the impact of the pressure difference between the working volumes, resulting in lower volumetric efficiency, complicated distribution of the flow field, and contributed to the formation of a considerable number of vortex. The vortex formed due to leakage is a major component of the supercharger’s flow loss through the analysis of the flow characteristics of the supercharger.When the rotational speed is constant, the pressure difference between the various working volumes larger and leakage further increased which making the volumetric efficiency of the supercharger to reduce with the pressure ratio increases, through the analysis of the characteristics curves of the twin-screw supercharger. Under a certain pressure ratio, improving the speed can make up the low volumetric efficiency by the gap caused. Supercharger’s adiabatic efficiency with the speed change was first increased and the decreased, which peaks of approximately45%in about7000r/min.