THREE-DIMENSIONAL VANELESS DIFFUSER ROTATING STALL NUMERICAL STUDY

摘要

Centrifugal compressor efficiency is the key to increasing incomes from its operation. There are several flow instabilities which can negatively affect a compressor, one of them being the rotating stall, as it decreases efficiency and mass flow while it can also lead to a surge. Among others, this can occur in the vaneless diffuser. A thorough understanding of this phenomenon and the ability to model its behaviour can lead to a robust protection system assuring high efficiency even at lower mass flow rates. In this paper, the simulated flow was viscous and compressible. Much attention was devoted to providing boundary conditions that would not affect flow conditions at the diffuser outlet. The transient simulation was conducted in order to observe sequential stages of the VDRS onset and growth. Pressure signals from different points in the diffuser have been analysed with the CWT method in the purpose of detecting oscillations frequency change in time. Results have shown that the complex structure and time evolution of the VDRS indeed require the application of three-dimensional methods. As the mass flowrate was continuously decreased a sudden change in number of the rotating stall cells was observed together with an appearance of new strong peak of the pressure oscillation.