Abstract
The study presents the simulation results of the viscid gas flow in low flow coefficient centrifugal compressor stages. The problem is solved in a stationary formulation using the Ansys CFX software package. The numerical simulation is carried out on three ultrahigh-pressure model stages; two stages have blades of the classical type impeller and one stage is of the bodily type. The value of the conditional flow coefficient is 0.0063 to 0.015. As part of the study, block-structured design meshes are used for all gas channel elements, with their total number being equaled as 13–15 million. During the calculations a numerical characteristic was validated with the results of tests carried out at the Department of Compressor, Vacuum and Refrigeration Engineering of Peter the Great St. Petersburg Polytechnic University. With an increase of inlet pressure as a result of a numerical study, it was found that for a given mathematical model the disk friction and leakage coefficient (1 + βfr + βlk) is overestimated. The analysis of flow in labyrinth seals has shown an increase of total temperature near the discs by 30–50 °С, nevertheless this fact did not influence gas parameters in the behind-the-rotor section. The calculation data obtained with finer design mesh (the first near-wall cell was 0.001 mm) is identical to those obtained with the first near-wall cell 0.01 mm mesh.
Highlights
Low flow coefficient centrifugal compressors are used to obtain high and ultrahigh gas pressures, which is necessary for modern gas transport systems
As a result of this are narrow flow sections, small hydraulic diameters, and low Reynolds numbers. This fact was confirmed in works [1, 2, 3], related to the thermo-gasdynamic principles ultrahigh-pressure centrifugal compressors design and experimental studies
Low flow rates with small channel sizes require increased manufacturing accuracy and minimal surface roughness, which leads to additional cost increases
Summary
Low flow coefficient centrifugal compressors are used to obtain high and ultrahigh gas pressures, which is necessary for modern gas transport systems. As a result of this are narrow flow sections, small hydraulic diameters, and low Reynolds numbers. This fact was confirmed in works [1, 2, 3], related to the thermo-gasdynamic principles ultrahigh-pressure centrifugal compressors design and experimental studies. The unsteady nature of the gas flow in the stage of a centrifugal compressor plays an important role. In the work [4] showed that the amplitude of the pressure change in the peripheral sections of the impeller reaches 4 MPa. According to the results of calculating the unsteady flow in the work [1], a conclusion was made about the undesirability of using traditional design blade diffusers. Low flow rates with small channel sizes require increased manufacturing accuracy and minimal surface roughness, which leads to additional cost increases
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