Ice Crystal Icing: Particle Impact, Accretion and Shedding

Ice-crystal icing in gas turbines is governed by two coupled scales: the impact and breakup of individual microscopic ice particles, and the accretion and shedding of macroscopic ice layers formed from ice-crystal clouds. These transient interactions strongly influence engine performance, yet key processes—especially restitution of non-spherical particles and accretion on heated surfaces under glaciated conditions—remain insufficiently quantified. This dissertation presents a unified experimental investigation across both scales using shared wind-tunnel facilities adapted for continuous, size-conditioned particle injection, together with automated multi-view image analysis for fragment and kinematic extraction. The first part examines single-particle impact mechanics. High-speed multi-view recordings of spherical and non-spherical ice particle impacts on aluminum and ice substrates produced a large dataset spanning 50 µm – 1500 µm particles with impact velocities of 0 m/s – 80 m/s and particle temperatures of -20 °C to – 10 °C. A new restitution framework was derived that incorporates particle size, temperature, and the effective substrate–particle elastic modulus into a consistent scaling. Normalizing the impact velocity by a critical fragmentation velocity Uc and the restitution by a quasi-elastic plateau eqe collapses all available spherical-particle datasets—literature and new—onto a single curve, rendering aluminum and ice substrates indistinguishable within this normalization. Within this reduced-velocity framework, the largest-fragment diameter follows a universal and substrate-independent transition curve that captures the progression from intact rebound to progressive comminution. Using the same normalization, an energy-based analysis decomposes the rebound of the largest fragment into normal, tangential, and rotational kinetic energy fractions. A global transition model then quantifies how this energy redistribution changes with impact severity, providing a consistent reference for spherical particles and revealing the additional geometry-driven coupling introduced by non-spherical impacts. A complementary oblique-impact campaign with non-spherical particles shows that normal restitution remains nearly angle-independent, whereas tangential response and rebound angle increase with incidence angle. By conditioning the analysis on fragmentation severity, the combined influence of impact angle and breakup on rebound behavior is captured. The second part investigates mixed-phase and fully glaciated ice accretion on heated NACA 0012 airfoils. A broad matrix of engine-relevant airspeed, temperature, particle size, ice-water content, and heat flux was tested, with particular emphasis on negative wet-bulb conditions on warm substrates. The results show that substantial accretion and shedding occur even for fully glaciated clouds, and that substrate heat flux is the dominant regulator of ice-layer growth, structure, and stability. Two distinct shedding regimes were identified: melt-film-driven runback at positive wet-bulb temperatures, and cyclic detachment of semi-solid blocks at negative wet-bulb temperatures. Combining these data with prior work yields a global accretion limit in particle-size–velocity space that separates accreting from erosion-dominated conditions. Together, the results provide a physically grounded description of both microscopic impact behavior and macroscopic ice-layer evolution. The datasets, scaling laws, and physical interpretations form a basis for improved numerical modeling and mitigation strategies for aircraft and engine icing.