Heat and Mass Transfer Characteristics of Water Droplets in Wet Compression Process

Abstract

Wet compression technology is an economic and effective approach to improve the performance of gas turbine. In the process of wet compression, the gas turbine engine will ingest a certain amount of water, which can influence the overall performance of the engine. Thermodynamic process and performance of compressor are influenced significantly by heat and mass transfer of the injected water droplets. This study is a new research of investigating theoretically the water droplets effects on the heat and mass transfer characteristics. It focuses on the aerodynamic and thermodynamic effects of the two-phase flow in the compressor stage. The application of Computational Fluid Dynamics (CFD) is the basic method to examine the details of the flow in an axial compressor stage and how it is affected by the presence of water, especially by the water droplets. The computation of water droplets characteristics, are provided by a simulation model of the code named CFX. Considering the change in aerodynamics and thermodynamics feature due to the water droplets, the compressor stage’s performance variations are analyzed. The movement and the evaporation of the water droplets in a compressor stage are simulated and analyzed by using unsteady numerical methods under different water injecting conditions in this paper. The movement characteristics of water droplets in compressor passage are investigated to understand the flow mechanisms responsible for wet compression formation process. The investigation of water droplets in compression can help to understand some phenomenons by using wet compression technology. The flow of water droplets between rotor blades are analyzed by using computational fluid dynamics method. Full coupling between gas and water droplets are adopted, allowing gas and water droplets to affect each other. Many motion parameters of water droplets are researched, such as slip velocity, Weber number and Reynolds number. The forces acting on water droplet are also discussed. Aerodynamic breakup of water droplets and interactions between water droplets and wall are taken into consideration at the same time. The results indicate that: (1) The motion of water droplets in compression areor mainly controlled by drag force. The motion parameters of water droplets changes mostly at the entrance of flow passage between rotor blades, and the turbulence intensity and breakup strength of water droplets reaches their maximum at the entrance. (2) The flow angle of water droplets is bigger than gas in rotor region due to their inertia, which can explain why water droplets have bigger separation degree and are easier to flow toward blade pressure surface. (3) The motion of water droplets in stator region is also important to be investigated for wet compression, and the motion analysis of single water droplets between blades is still needed to be developed, so more investigation will be carried out.