| Popis: |
Numerous supercooled droplets and/or ice crystals exist in a cloud. When an aircraft passes through a cloud, they impinge on the aircraft wing and fuselage, and also they enter into the jet engines. Such impinging droplets and ice crystals can form ice layers on the surfaces. This phenomenon is referred to “icing.” Apparently, the icing adversely affects the performance of an aircraft by reducing the lift and thrust, and it may cause a crash. To predict and understand the icing, a number of major research institutes and companies have been investigating the icing both experimentally and computationally. However, the icing is still one of major issues in the research and development processes of an aircraft and a jet engine because of the complicated interactions among various physical and weather conditions. In a jet engine, the main icing components are the fan blade, the fan exit guide vane (FEGV), the nose cone, the splitter, and the low-pressure compressor. Recently, the ice crystal icing in the high-pressure compressor attracts much attention because the ice crystal icing has been known as one of the major causes of engine power loss events in flight. The mechanism of the ice crystal icing is as follows: the ice crystals partially melt as they pass through the fan and the low-pressure compressor where the static temperature varies approximately from −30 to 100 (°C); the ice crystals impinge on the wall and create a water film on the warm surface of the components; the water film traps additional ice crystals, and the surface is cooled below the freezing point; the additional ice layer is build up on the surface. However, since the physics is so complicated, the ice crystal icing has not been predicted satisfactorily. In the present study, first, melting behavior of an ice crystal passing through a fan and a compressor of a jet engine was investigated. Since the ice crystal icing tends to occur in a high-bypass ratio jet engine, GE90 was selected as the target engine. In the simulations, thermal conduction, heat transfer, and evaporation were taken into account. The influences of ice crystal diameter and cruising altitude were focused to discuss the melting process of ice crystals under actual operational conditions. Second, using the computational results, we numerically investigated the possibility whether ice crystal icing actually occurs or not in the compressor. Icing on a two-dimensional compressor stator blade in a high-temperature environment was computed. Following conditions were assumed: the cruising altitude is 6000 (m), the material of blade is aluminum, and the diameter of an ice crystal is 100 (μm). We confirmed that the ice crystals that are half melt impact to the stator blade, cool it to the temperature lower than the freezing point, and form an ice layer on the leading edge. |
