The results of computational investigation of the influence of a gas labyrinth seals, oil end seals with floating rings and oil journal bearings lubricating layer stiffness coefficient on centrifugal compressor rotor critical speed are presented and analysed. The main principles of a method for axial forces acting on centrifugal compressor rotor calculation are listed. The method has been developed at the compressor, vacuum and refrigeration technologies department of SPbSTU. In addition, the estimation of method applicability in engineering calculations is given.

The article presents the results of a numerical study of the effect of equivalent sandgrain roughness on the characteristics of a low-flow centrifugal compressor stage. Low-flow stages are widely used in high-pressure compressors as the last stages. These compressors are used for natural gas booster compressor stations, as well as in technological processes for the production of methanol, ammonia, high - pressure polyethylene, etc. The efficiency of the low-flow stages is lower than that of medium-and high-flow centrifugal compressors stages. Stages operate at high pressure and have low gas volume flow rates. For this reason they have narrow channels of the flow part, significant friction and leakage losses. The study was conducted in the Ansys CFX 19.2 software package. In the first part of the study, the low-flow stage numerical model is validated with the test results. Full-scale tests of the stage were carried out at the LPI-SPbPU earlie. In the second part of the study, impeller equivalent sand-grain roughness numerical study carried out. As a result, the characteristics of the stage were obtained at four different values of equivalent sand-grain roughness ks. The impeller losses were estimated. It is established that when the ks values increase, the polytropic head and efficiency values do not decrease equally over the entire characteristic. Characteristics are significantly reduced in areas of high expenditure and change slightly with minimal expenditure. The internal head coefficient varies slightly depending on ks.

The paper presents the results of numerically investigating viscous gas flow in a simulated low-discharge stage of a super high-pressure type compressor, using the ANSYS CFX software package. We studied the low-discharge centrifugal compressor stage prototype designed and tested at the Compressor, Vacuum and Refrigerating Technology Department of Peter the Great St. Petersburg Polytechnic University. In order to conduct the numerical experiment, we performed a mesh independence study. We compared the properties obtained in the numerical investigation to the experimental data. In our mathematical simulation the magnitude of the axial clearance between the covering disc of the runner and the compressor body varies in the range of 1--5.5 mm; we estimate the effect that varying this number has on the loss complex characteristic 1 + βfriction + βleakage

The article presents the results of a numerical study of the influence of the theoretical head coefficients on the characteristics of a low-flow stage of a centrifugal compressor. The study was conducted in the Ansys CFX 19.2 software package. As a result of a numerical study, it was found that the drop in the efficiency of the compressor stage with an increase in the theoretical head coefficient is associated with a decrease in the efficiency of the stationary elements due to the increased absolute speed behind the impeller. At the same time, an increase in the theoretical head coefficient leads to a decrease in losses associated with the coefficient 1 + β1k + βfr and therefore, an increase in the polytropic efficiency of the impeller is observed at values of the theoretical head coefficient ψt ≤0.64.