Performance degradation characteristics of subsea gas–liquid multiphase compressors based on loss breakdown analysis

This study presents the design of a novel counter-rotating axial wet gas compressor tailored for the operating conditions of deepwater gas fields in the South China Sea. Through high-fidelity numerical simulations and experimental validation, the performance evolution characteristics and underlying mechanisms of the compressor under gas–liquid two-phase flow conditions are investigated. Crucially, the presence of wet natural gas is found to exert a pronounced detrimental impact on the compressor's performance, causing an approximately linear decrease in polytropic efficiency as the liquid mass fraction (LMF) increases. When the inlet pressure is 25 bar, and the LMF is 7%, the efficiency decreases by 2.5% points; when the inlet pressure is 1 bar and the LMF is 7%, the efficiency decreases by 4.38% points. The mechanism of performance degradation lies in the fact that droplets migrate toward the blade tip under centrifugal force and impinge on the leading-edge region, forming a localized accumulation. This accumulation reduces the mainstream Mach number through a drag effect, enlarges the wake region, and enhances vorticity and turbulent kinetic energy, ultimately triggering significant flow separation and unsteadiness, which leads to performance degradation. Further loss breakdown analysis shows that the total entropy generation rate continues to increase after the introduction of the liquid phase, rising from 1.29 × 107 W/K under dry conditions to 1.92 × 107 W/K when the LMF is 7%. In addition, the loss structure also changed significantly: the proportion of end wall loss decreased, while the proportion of profile loss (from 3.46% to more than 11%) and leakage loss (from 16.53% to 20.72%) increased significantly, indicating that the interaction between droplets and the wall is the key mechanism that exacerbates flow dissipation. In summary, droplets significantly increase irreversible flow losses within the compressor, particularly over the blade surfaces and in the leakage regions, through processes such as inertial impaction, aggregation and breakup, and enhanced gas–liquid mixing and momentum exchange, leading to a decline in overall compressor performance. This study provides an important theoretical basis for the optimal design and stable operation of a deep-sea gas–liquid mixed-transport rotary compressor.