The study of y+ influence on the results of nozzle flow numerical simulation in the centrifugal compressor inlet chamber

The efficiency of compressor machines for refrigeration needs is characterized by the efficiency coefficent. Increasing the efficiency of the stage is necessary, especially for centrifugal compressor machines. In this paper, the study of the centrifugal compressor inlet radial chamber, which directly affects the efficiency of the entire stage, is carried out. A mathematical model has been selected for conducting a numerical experiment with its subsequent validation with a full-scale experiment. The selection of the mathematical model included grid independence study, boundary conditions selection, and the study of the y + wall function influence for a specific turbulence model. y + is an important factor in numerical experiments, and its incorrect choice can lead to a non-physical flow pattern. There are certain recommendations for the y + value for different turbulence models. However, as this study is shown, the existing recommendations are not universal for different centrifugal compressors flow parts. Recommendations on the value of the y + parameter for inlet chambers with different nozzle values at different Reynolds number values are investigated and given in this paper. To determine the losses dependence function form on the average y + value, the results of calculations are summarized in separate graphs and approximated by separate functions. Approximation dependence is obtained based on the numerical experiment results of the average y + value influence, the chamber nozzle coefficient and the Reynolds number on the losses of the inlet radial chamber. The obtained dependence was used to determine the optimal value of y + mean and the wall layer for experimental studies of chambers. The results of the numerical experiment are compared with the results of the full-scale experiment and experimental dependences are obtained. The results obtained will simplify further work on modeling the inlet radial chambers.