Effects of tip water injection on near-stall flow structure and performance of a transonic compressor

Abstract

Near-stall operation of transonic compressors is critical for achieving high pressure ratio and efficiency, but it is accompanied by sensitive tip-region flow structures that strongly affect compressor performance. Discrete water injection near the blade tip is investigated as an active flow-control method to modify the near-tip flow field at a representative near-stall operating condition of a transonic axial compressor. Three-dimensional unsteady Euler–Lagrange multiphase simulations are performed for NASA Rotor 37. The carrier phase is solved using the unsteady Reynolds-averaged Navier–Stokes equations, while water droplets are tracked in a Lagrangian framework with two-way coupling of momentum, heat, and mass transfer. Representative spray conditions are used to examine the coupled compressor–spray response. The results show that tip water injection increases the compressor mass flow rate and adiabatic efficiency by approximately 3% and 5%, respectively, with only a minor change in total pressure ratio. Comparisons between evaporating and non-evaporating cases distinguish two concurrent mechanisms: axial momentum addition from the injected droplets and evaporative cooling of the near-tip flow. Together, these mechanisms induce a coupled reorganization of the near-tip flow through droplet momentum exchange and tip-region loading redistribution, which weakens leakage-jet penetration, moderates vortex roll-up and tip separation, and suppresses the near-tip recirculation zone, thereby reducing blockage and aerodynamic loss. Droplet-size analysis shows that breakup and evaporation govern downstream spray evolution and droplet–flow interaction. These findings clarify how discrete tip water injection modifies near-tip flow behavior and promotes a more robust compressor response at the investigated near-stall condition.