Effects of droplet loading and size on droplet–particle interaction and loss mechanisms in a CAES-oriented transonic compressor

Compressors are core components of compressed air energy storage (CAES) systems, where aerodynamic efficiency and fouling resistance directly influence charging power consumption and overall energy storage performance. Under humid and polluted ambient intake conditions, compressors may ingest airborne droplets and solid particles simultaneously, leading to flow distortion, blade fouling, and additional aerodynamic losses. Understanding the coupled multiphase mechanisms governing these effects is therefore essential for improving compression efficiency and operational reliability in CAES systems. In this study, droplet–particle interaction and loss mechanisms in a CAES-relevant transonic compressor (NASA Rotor 37) are numerically investigated using a hybrid Euler–Euler–Lagrangian multiphase framework that simultaneously resolves gas–droplet momentum exchange, particle transport, and particle–wall interactions. The results reveal that droplet ingestion significantly modifies transonic flow structures and compressor loss characteristics. Large droplets (10 μm) intensify the interaction between the tip-leakage vortex (TLV) and the passage shock, strengthening shock-induced separation and increasing entropy generation in the tip region. As a result, the peak pressure ratio decreases by approximately 6.6% near stall, while isentropic efficiency drops by about 4%. In addition, larger droplets increase particle impact velocity and incidence angle, producing deposition rates up to 250% higher than those under dry conditions. In contrast, smaller droplets (3 μm) partially mitigate deposition by dissipating particle kinetic energy and suppressing severe wall impacts. These findings demonstrate that droplet-modified TLV–shock interaction is the dominant mechanism linking aerodynamic loss and particle deposition under humid pollutant conditions, providing useful guidance for intake-condition management and fouling-resistant design of compressors.