Ice crystal icing in gas turbine engines

Numerous turbofan power loss events have occurred in high altitude locations in the presence of ice crystals. Ice crystals enter the engine core, partially melt in the compressor and then accrete onto components that are initially warmer than freezing. The ice accretion causes blockage of the flow path, and if it later sheds can damage downstream components and potentially cause flame-out alongside other issues. Numerical models are currently required for the design and certification of next-generation engines to fly within ice crystal icing conditions. They have successfully predicted ice growth on simplistic geometries, but are often fine-tuned to a single condition or geometry due to the high level of empiricism. In this thesis a review of the current literature is presented, areas of missing research are indicated, some of which form the basis of the PhD. First, a new method for spatially resolving the three-dimensional ice accretion profile was developed and tested in an ice crystal icing wind tunnel. Historical measurement techniques were either two dimensional or could only be applied after the accretion had formed. This new technique provides transient, three-dimensional, non-intrusive measurement of the accretion during the ice exposure. Such measurements are deemed essential for the development of complex three-dimensional ice accretion models. The second set of work was the development of the ice crystal icing numerical model, ICICLE. The most notable development was the inclusion of the ability to update the flowfield based on the numerically predicted accretion profile. This change in geometry alters the potential field, leading to changes in the predicted particle trajectories and resultant accretion. The new capabilities of the code were tested using two test pieces: a single compressor stator, and a triple NACA airfoil linear cascade. The results showed that certain conditions require the update of the flowfield for accurate estimation of both the shape and volume of the accretion.