Eulerian method for ice crystal icing in turbofan engines

摘要

The newer generations of high-bypass-ratio engines are susceptible to the ingestion of small ice crystals which may cause engine power loss or damage. The research presented in this thesis focusses on the development of a computational method for in-engine ice crystal accretion. The work has been carried out in the framework of project High Altitude Ice Crystals (HAIC), co-funded by the European Union. The developed ice accretion method is split in the numerical simulation of three distinct parts of the process: particle trajectories towards an object, particle impact on the object's surface and evolution of the ice layer on the surface. An Eulerian method has been applied to calculate the trajectories of the (melting) ice crystals. The trajectory method includes models which account for the effects of the shape of the ice crystal on its trajectory and on the heat transfer to and from the particle as well as phase change along its trajectory. On impact with a surface the ice crystals can either bounce from the surface, break-up into a number of smaller fragments or stick to the surface. An impact model has been applied which relates the impingement characteristics to the amount of water that is present in the form of (supercooled) droplets or melted ice crystals. In the last part of the method the mass flux of impinging ice crystals is used to determine the ice layer by solving the mass and energy balance in control volumes along the surface along with accounting for erosion caused by the impinging ice crystals. The method for ice crystal icing has been validated employing available experimental data. The computation of the change of the particle phase has proven to be accurate. The method for ice accretion has proven to be fairly accurate in both glaciated (cloud with ice crystals) and mixed-phase (cloud with ice crystals and liquid droplets) icing conditions.