An unsteady tightly-coupled icing model is established in this paper to solve the numerical simulation problem of unsteady aircraft icing. The multi-media fluid of air and droplets is regarded as a single medium fluid with variable material properties. Taking the droplet concentration as the phase parameter and the droplet resistance coefficient as the interphase force, the mass concentration distribution of the droplet is obtained by solving the Cahn–Hilliard equation. Fick’s law is introduced to improve the Cahn–Hilliard equation to predict the droplet shadow zone. On this basis, the procedure of the unsteady numerical simulation method for aircraft icing is established, including grid generation, the dual-time-step method to realize the unsteady calculation of the air and droplet tightly-coupled mixed flow field, and the improved shallow water icing model. Finally, through the comparative analysis of numerical examples, the effectiveness of the new model in predicting the droplet impact characteristics and the droplet shadow zone are verified. Compared with other icing models, the ice shapes predicted by the unsteady tightly-coupled model were found to be the most consistent with the experiments. In the icing comparison conditions in this manuscript, the prediction accuracy of the ice thickness at the stagnation point of the leading edge was up to 35% higher than that of LEWICE.

Icing phenomena are one of the hot issues in the aviation field, which has attracted the attention of many manufacturers. The physical process of water film flow determines the position and amount of icing. In this paper, the flow process of water film on a rough surface is studied. An experimental platform was built in a wind tunnel, and the digital image processing (DIP) technology was used to measure the water film flow. The water film flow under different roughness conditions of the plate was obtained in the experiments. The correction model of interfacial shear coefficient is established, and the influence of roughness on water film flow is deduced. The relationship obtained in this paper can provide data support for the study of gas-water coupled flows on rough surfaces.

A series of experimental studies were conducted to explore the fluctuation characteristics of the water film under the air flow condition with the research background of the anti-icing system. The dynamic measurement of the water film on the surface of the aluminum-based plate was achieved using the digital image projection measurement technology. The influence of diverse wind speeds and Reynolds numbers on the average water film thickness, fluctuation intensity, and velocity of the liquid film was analyzed. The piecewise characteristics of the wind speed and Reynolds number for the fluctuation characteristics of the water film were analyzed innovatively. The fluctuation characteristics and formation principle of each stage were also examined. The results had a significant impact on establishing and modifying the mesoscopic models of aircraft icing to improve the design methodology of the anti-icing process.

Multi-Zone Ice Accretion and Roughness Models for Aircraft Icing Numerical Simulation - Volume 8 Issue 5 - Chengxiang Zhu, Chunling Zhu, Tao Guo

Icing phenomena occur on aircraft and unmanned aerial vehicles (UAVs) under extreme weather conditions. Ultrasonic detection technology is an effective method for measuring ice formation while maintaining the shape of the structure. However, current ultrasonic sensors, which are large and inflexible, are unsuitable for irregular UAV bodies, limiting their applications in real scenarios. For the detection of icing on curved structure, this study proposes a novel flexible ultra-thin ultrasonic transducer (FUTUT). The transducer exhibits excellent flexibility, making it suitable for use on high-curvature wings. Firstly, the FUTUT was designed based on the material properties of the airframe and the sensitivity requirements for ice detection, following the design guidelines for 1-3 type piezocomposites. The fabrication process for the FUTUT was then investigated, and its flexibility and low-temperature resistance were tested. Finally, icing detection experiments were conducted in an icing wind tunnel (IWT), where the FUTUT of 9.82 MHz demonstrated an ice-thickness-detection sensitivity of 0.29 mm. Experimental results indicate that the FUTUT possesses superior flexibility and exhibits excellent stability in low-temperature environments. These results underscore the FUTUT’s promise for applications in ice detection on curved structures.

Ice accretion on the inner surface of a fuel tube can fall off and potentially block the filters and small orifices, which thereby restricts the fuel flow to the engines during the long flying of the aircraft in cold conditions. This might cause the engines to shut down and pose a catastrophic safety threat. In this pursuit, the present study evaluates the effects of fuel temperature, entrained water concentration, and duration on the accretion of ice in flowing super-saturated RP-3 aviation jet fuel. A methodology for the quantitative mixing of water mist with fuel for accurately controlling water concentration was proposed. The different kinds of accreted ice, ‘fluffy’ and ‘pebbly’, were observed. As the distance of flow increased, a non-uniform distribution of ice on the cross-sectional area was noted. The amount of ice accretion increased with a decrease in the temperature from −2 °C and −12 °C, and with an increase in entrained water concentration. Besides, the amount of ice accretion showed an increasing trend as time went on and became stable after 2 h. Our experimental results can assist to gain a better understanding of the ice accretion process in flowing super-saturated fuels and may serve as a basis for the design of the aircraft fuel system and airworthiness certification.