Numerical Simulation of Ice Crystals Growth in Turbofan Engines

A series of high-altitude turbofan engine malfunctions characterized by flameouts and sudden power losses have been reported in recent years. The cause of these incidents has been hypothesized to be the ingestion of ice crystals in the engine core which have been lifted to high altitudes by strong convection cells. Crystal icing in the engine core has posed a significant potential threat to operational aircraft safety. Therefore, understanding and mitigating the associated risk is paramount to engine manufacturers. Its importance has motivated considerable research and development efforts from industry and academia to characterize and quantify the phenomena, determine the onset of accretion on a given engine component and characterize the local conditions causing it. To help understand the phenomenon using simulation, a CFD methodology that characterizes the potential ice accretion due to melting crystals will be presented. Fundamental validation studies on an unheated cylinder and NACA0012 airfoil provide a basis for more complex validation studies on an experimental rotating rig. A complex 3D turbomachinery geometry will then be used to demonstrate ice crystal accretion in a high-fidelity workflow where important thermodynamic effects, such as crystal melting, their contribution to evaporation and the vapor phase, and interactions with the surface that include post-impact re-entrainment will be considered. In addition, a multishot icing analysis is included to improve the accuracy of the ice accretion and better represent the ice blockage between vanes. Finally, the change in engine performance parameters, such as core total pressure ratio, mass flow rate, bypass ratio, and stage efficiency will be calculated as an indicator of engine risk.