Aerodynamic optimization of subsea counter-rotating compressors based on parametric dimensionality reduction method

Abstract

This study addresses the challenge of achieving efficient deep-sea (500–1500 m) pressurization through the aerodynamic optimization of subsea wet-gas axial compressors based on a counter-rotating design. A novel aerodynamic optimization framework is introduced, integrating parametric dimensionality reduction with a multi-objective genetic algorithm. Six key dimensionless parameters, hub-to-tip ratio, span-to-chord ratio, m-to-l ratio, chord length stacking ratio, stagger angle stacking ratio, and camber angle stacking ratio are defined, together with four fundamental design parameters: number of blades, shroud diameter, stagger angle at hub and camber angle at hub. This formulation reduces the number of design variables from 78 to just 10, thereby streamlining the design process and minimizing the occurrence of unrealistic geometries during sampling. Sensitivity analysis indicates that the hub-to-tip ratio exerts a dominant influence, accounting for over 50% of the variation in both pressure ratio and polytropic efficiency. Following optimization, compressor performance under gas-liquid two-phase flow conditions improved substantially. Compared with the initial design, the optimized configuration achieved a 12.04% increase in polytropic efficiency (from 76.4% to 85.6%) and a 4.04% increase in pressure ratio (from 1.09 to 1.134). Notably, this performance gain enables the target pressurization range of 22–27 bar to be achieved using only 10 counter-rotating stages, satisfying all design requirements. Flow field analysis indicated that the performance degradation in the original design was primarily attributable to a detrimental horseshoe vortex formed at the trailing edge of the second-stage rotor blade, which led to liquid accumulation near the shroud and obstructed downstream flow. The optimized design successfully eliminated this vortex and promoted a more uniform axial distribution of the liquid phase, demonstrating enhanced wet-gas handling capability. Additionally, stress analysis confirmed the stable operation of the optimized blades. Together, these results establish an efficient and reliable design methodology for counter-rotating compressors intended for deep sea applications.