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- Computational Modeling of Water Droplets Under Cooling and Freezing ConditionsPublication . Meireles, Rúben D. S. O.; Magalhães, Leandro; Silva, A. R. R.; Barata, Jorge M MThe crystallization of water droplets is a ubiquitous phenomenon, which plays afundamental role in many natural and artificial processes. This phenomenon gainedparticular interest in the aeronautical industry due to ice accretion on lifting surfaces andengine intakes. A performance study is made of several models for predicting cooling and freezing phenomena, ranging from one- and two-way coupling to full-fledged four-stage freezing methodologies. First, a performance study is made of the one- and two-way coupling methodologies in the portrayal of the interaction of the particles and the surrounding gas on free-falling water droplets with diameters ranging from 3 to 6 mm and relative humidity ratios of 0.29, 0.36. 0.52 and 1.00. Then a generalized four-stage freezing model is implemented, where the temperature evolution of a suspended water droplet is tracked, adding to the cooling in the free-falling conditions, the recalescence and solidification stages. The results indicate that, for high relative humidity ratio, the interaction particles-medium is preponderant and needs to be accounted for, which does not take place for low relative humidity ratios, where one-way coupling seems to be suitable approximation. Lastly, the full stage freezing model was able to capture the experimental trend of recalescence and solidification stages.
- Characterization of a Two-way Coupling Approach for the Simulation of Fluid Flows under Cryogenic ConditionsPublication . Meireles, Rúben D. S. O.; Magalhães, Leandro; Silva, A. R. R.; Barata, Jorge M MIce formation at lifting surfaces and engine intakes is a significant issue affecting regular aircraft operation. The icing on a wing’s leading edge perturbs the airflow around the wing, contributing to a decrease in lift and increasing drag. A step towards the understanding of droplet dynamics under cryogenics is made in the present work. An in-house developed tool is used to study the impact of droplet diameter and air humidity ratio in free-falling water droplets’ flow dynamics. The 3D Navier-Stokes equations are solved in a RANS-based two-way coupling model, which considers that the carrier fluid properties are modified by the presence of a dispersed phase, accounting for mass exchange momentum and energy between them. A Lagrangian/Eulerian formulation is employed to model each of the considered phases. The results obtained are compared with a one-way modeling approach and experimental data to infer the interacting phases’ effect in the overall process dynamics. In this way, it is possible to conclude that for high humidity content, this interaction is predominant and, consequently, needs to be taken into consideration. However, for low humidity ratios, the one-way coupling is a sufficient approximation to the experimental data.
- Numerical Modeling Of Freezing Water DropletsPublication . Magalhães, Leandro; Meireles, Rúben D. S. O.; Silva, A. R. R.; Barata, Jorge M MThis work enhances the understanding of droplet dynamics under cryogenics conditions through an in-house developed analytical tool used to predict the supercooling of water droplets. The physical process is based on a full-scale four-stage supercooling process in which the recalescence stage is assumed instantaneous and the crystallization kinematics of the droplet neglected. The transition temperature of each stage is obtained, resorting to a theoretical balance for the droplets internal energy against the heat loss to the environment. In this way, the representation for the droplets temperature curves alongside the time. The droplets are considered spherical, and the internal motion is so vigorous that complete mixing occurs. The droplets convective effects are accounted for using the Ranz-Marshall classical formulation.