Effect of Water Injection on Turbofan Engine Compressor Operation and Aerodynamics

Abstract Water injection (WI) can potentially remedy aircraft-related nitrogen oxide (NOx) pollution around airports and substantially extend the hot section’s life. No high-fidelity study exists examining the effects of deploying compressor water injection (CWI) on turbofans — an engine type dominating the civil aviation market. The available analytical work is bound to several limitations, such as uniform droplet size distribution, simplified droplet transport and no phase coupling. Effects of local changes in the gas composition, interaction of turbulence with dispersed phase and the underlying loss production mechanism of wet compressions are neglected and thus remain unquantified. The present work investigated the effect of WI on key performance and aerodynamic parameters in a fully integrated compressor of a generic turbofan engine using Computational Fluid Dynamics (CFD) analysis. The compressor layout comprised a fan stage and two core stages called booster. Water was injected behind the fan rotor at the inlet to the booster. Take-off operation was simulated at dry conditions and a range of wet scenarios with 1% and 2% water-to-air mass injection rates and varying droplet diameters from 10 to 20 microns. Effects on the stage-by-stage compressor performance are discussed in detail, including water distribution, mass flow, temperature, pressure ratio, and efficiency. Particular attention was paid to the aerodynamic effects, which are impossible to obtain based on analytical results. Furthermore, the detailed droplet evolution inside the compressor was scrutinised, including particle residence time, change in size and distribution due to evaporation and interaction with compressor flow and components. The outcomes showed that water injection can result in favourable conditions for compressor operation. Furthermore, a reduction in compressor delivery temperature of up to 40 degrees Kelvin was predicted if finely atomised water was injected.