Numerical Modelling of Primary and Secondary Effects of SLD Impingement

A CFD simulation methodology for the inclusion of the post-impact trajectories of splashing/bouncing Supercooled Large Droplets (SLDs) and film detachment is introduced and validated. Several scenarios are tested to demonstrate how different parameters affect the simulations. Including re-injecting droplet flows due to splashing/bouncing and film detachment has a significant effect on the accuracy of the validations shown in the article. Validation results demonstrate very good agreement with the experimental data. This approach is then applied to a full-scale twin-engine turboprop to compute water impingement on the wings and the empennage. Since the performance characteristics of twin-engine commercial turboprops are such that they operate most efficiently at flight levels where SLD encounters may occur, the goal of this article is to establish a 3D computational methodology to eventually enable a complete study of the impact of FAR 25 Appendix O on the IPS requirements for this class of airplanes. The Appendix O icing conditions used for the demonstration of the methodology are set for a turboprop in a typical holding pattern at 6,000 ft, 190 kts, and 5° angle of attack. The air static temperature is 268 K and the LWC is 0.3 g/m³. Freezing drizzle environments are considered for the MVD > 40-micron droplet distributions. The results for these flight conditions show that inclusion of the secondary impingement due to splashing/bouncing in the simulation accounts for an increased water catch by 4.12% on the wing inboard section and 7.61% on the vertical stabilizer.