Approaches to construction the grid spatial model of low-flow centrifugal compressor stages for simulation the viscous flow

The paper presents the problem of defining the flow part computational domain with computational fluid dynamics (CFD) RANS-method of a viscous gas on a low-flow centrifugal compressor stage. The conditional flow coefficient Φ of investigated stage is 0.008. Several variations of computational domain are considered: the main flow path; including the inlet pipe and fairing; accounting of cavities and labyrinth seals regions with full connection with flow path and one-sided connection at the impeller exit; computational domain with friction surfaces of large work disk base. It is shown that in the case of axial stage suction the inlet pipe and fairing do not have significant effect on flow parameters upstream the impeller and gas dynamic characteristics of the stage. The simulation without account of disk friction and leakage through labyrinths seals have unacceptable qualitative and quantitative result. The most relevant option to account disk friction and leakages is the full two-sided connection of work and shroud disk cavities with flow part, since the one-sided connection simulate only the disk friction and leakages well, but do not account the influence on the impeller flow. In some cases, it is important to take into account additional regions involved in friction losses. In addition, the influence of total pressure measuring tools placed in three section along the diameter is evaluated. It is concluded that the measuring tools have a minor effect compared to the other types and sources of low-flow stage losses. The task of flow path and cavities grid independence is considered. The cavities grid independence is important not less than the main flow path and blade rows. The influence of the dimensionless wall distance y+ of the first near-wall layer for low-Reynolds turbulence model Spalart-Allmaras is estimated.