Original Article Effects of water ingestion on the tip clearance flow in compressor rotors Lu Yang, Hai Zhang and Aqiang Lin Abstract The tip region of compressor rotors may be filled with water when aircraft is flying in heavy rain environment. In order to explore the effects of water ingestion on the compressor performance and the characteristics of tip clearance flow, the Euler–Lagrange method has been utilized to simulate the two-phase flow inside a transonic rotor (NASA rotor 35). The typical trajectory of water droplet in compressor has been introduced firstly to simply understand the situation of water ingestion and to verify the reliability of some special droplet breakup models. The simulation results show that water droplets will change the distribution of airflow parameters along the span direction, which leads to the decrease of mass flow rate and the increase of attack angle at the tip region, as well as the separation of boundary layer on the suction surface. Furthermore, the momentum losses caused by droplet impingement and breakup directly causes a sharp increase in the static entropy at the blade tip region. On the other hand, the ingestion of droplet brings an external disturbance to airflow, and although it has some dissipated effects on the turbulence kinetic energy, it aggravates the unsteady characteristics of turbulent flow seriously at the tip region. Finally, by comparing the compressor performance under wet and dry states, it can be concluded that the pressure ratio and adiabatic efficiency of compressor decrease after water ingestion, and the compression efficiency drops by 1–2% on the whole while the operating point moves forward and the stable working boundary becomes narrow. Keywords Water ingestion, tip clearance flow, wet compression, numerical simulation, transonic rotor Date received: 11 November 2017; accepted: 14 November 2018 Introduction Modern aircraft have always been required to possess the ability of flight in all weather conditions. As a consequence, the aero-engine has to deal with the challenges caused by a series of inclement weather, for instance, the engine may encounter a critical amount of liquid water during its intake process. 1,2 Unfortunately, the degree of concentration of liquid water is always greater than its normal value when the engine is operating at low engine speeds and high air- craft velocity conditions. This is called as the scoop effect in which the inlet area of airflow is relatively less than that of liquid water. 3 In addition, the existence of liquid water in the engine will pose some threats to the operational stability of compressor, combustion chamber, and turbine, which leads to local tempera- ture reduction, pressure losses, mechanical losses, surge, and even flame-out. 4–7 It is obvious that the ingestion of water droplets will move together with the main airflow to the com- pression component. 8 Following the movement of water droplets in compressor, the heat and mass transfer processes between water and the surrounding air are constantly occurring, which changes the work- ing environment of the compression system. 9,10 Although most droplets broken into smaller particles qualified for a better flow characteristic under the action of aerodynamic force and droplet–wall inter- action, the phenomenon of radial migration still occurred on part of droplets due to the centrifugal force. 11,12 On the other hand, droplets impinging on compressor blades will form a liquid film on them, and then it moves toward the casing due to centrifugal force and forms a thin liquid film again by the accu- mulation of water near the end wall. 13–15 However, the tip region of compressor rotor is a sensitive area that has a great influence on the com- pressor performance. 16 There are some complex flows Proc IMechE Part G: J Aerospace Engineering 0(0) 1–12 ! IMechE 2018 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/0954410018817688 journals.sagepub.com/home/pig Institute of Turbomachinery, Department of Power and Energy Engineering, Harbin Engineering University, Harbin, China Corresponding author: Hai Zhang, Institute of Turbomachinery, Department of Power and Energy Engineering, Harbin Engineering University, Harbin 150001, China. Email: zhanghai83821@163.com