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Accretion and shedding of ice layers is a serious problem for various engineering applications. In particular, ice layers growing due to ice crystal impingement on warm parts of an aircraft jet engine pose a severe hazard since they seriously affect safe operation of an aircraft. The material properties, and in the first place the strength of an ice layer, are crucial for the mechanisms leading to, and taking place during, both accretion and shedding of an ice layer. In the present study, the apparent yield strength of dry granular ice layers is examined employing a novel rigid-body-penetration approach. Dynamic projectile penetration into granular ice layers of varying porosity and ice grain size is experimentally investigated for different projectile impact velocities using a high-speed video system and post-processing of the captured video data.

Icing is a major hazard for aviation safety. Over the last decades an additional risk has been identified when flying in clouds with high concentrations of ice-crystals where ice accretion may occur on warm parts of the engine core, resulting in engine incidents such as loss of engine thrust, strong vibrations, blade damage, or even the inability to restart engines. Performing physical engine tests in icing wind tunnels is extremely challenging, therefore, the need for numerical simulation tools able to accurately predict ICI (Ice Crystal Icing) is urgent and paramount for the aeronautics industry, especially regarding the development of new generation engines (UHBR = Ultra High Bypass Ratio, CROR = Counter rotating Open Rotor, ATP = Advanced Turboprop) for which analysis methods largely based on previous engines experience may be less and less applicable. The European research project MUSIC-haic has been conceived to fill this gap and has started in September 2018.

Premature and uncontrolled flame initiation, called pre-ignition (PI), is a prominent issue in the development of spark-ignited engines. It is commonly assumed that this abnormal combustion mode hinders progress in engine downsizing, thus inhibiting development of more efficient engines. The phenomenon is primarily observed in highly turbocharged spark ignited (SI) engines in the full load regime at low engine speeds. Subsequent engine knock induces extremely high peak pressures, potentially causing severe engine damage. The mechanisms leading to this phenomenon are not completely understood; however, it is quite plausible that a multiphase process is responsible for the pre-ignition. One effect could be the interaction between injected fuel drops and the oil film on the cylinder liner. Under certain conditions, droplets of oil or oil/fuel mixture can detach or splash from the film, leading to pre-ignition at the droplet surface towards the end of the compression phase.

Airframe icing caused by supercooled large droplets (SLD) has been identified as a severe hazard in aviation. This study presents an investigation of impact of a supercooled drop onto superhydrophobic and partially wettable substrates. Drop impact, spreading and rebound were observed using a high-speed video system. The maximum spreading diameter of an impacting drop on partially wettable surfaces was measured. The temperature effect on this parameter was only minor for a wide range of the drop and substrate temperatures. However solidification hindered receding when both the drop and substrate temperatures were below 0°C. The minimum receding diameter and the speed of ice accretion on the substrate were measured for various wall and drop temperatures. The two parameters increased almost linearly with the decrease of the wall temperature, but eventually leveled off beyond a certain substrate temperature.

Numerical experiments have been presently conducted aiming at studying the influence of the surface energy on the crystallization process of supercooled water in terms of the supercooling degrees. The mathematical model consists primarily of the equation governing the thermal energy field solved independently in both phases in accordance with the two-scalar approach by utilizing the Stefan condition at the interface to couple both temperature fields. The computational algorithm relying on the level-set method for solid-liquid interface capturing has been appropriately upgraded aiming at accuracy level increase with respect to the discretization of the thermal energy equation and the normal-to-interface derivative of the temperature field. The model describes the freezing mechanism under supercooled conditions, relying on the physical and mathematical description of the two-phase moving-boundary approach.