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To characterize the performance of icephobic coatings for aerospace applications, various shear-based techniques have been used. Generally, these techniques are conducted in conjunction with comparison tests on metals. In this study, a review of the various approaches for measuring adhesion for static and impact ice for metal and icephobic surfaces was done. This review indicated that many details of the test conditions either varied significantly among studies or were omitted. To address this uncertainty, new measurements were taken to examine in-situ ice-shear-adhesion strength for impact and static ice with various surfaces, using a consistent icing-research-tunnel facility with well-characterized and detailed test conditions. The results for the two different metals tested revealed a significantly higher ice adhesion for static ice compared to that for impact ice. However, the tested self-lubricated icephobic coating significantly reduced ice adhesion strength for both impact and static ice and this performance was retained after multiple icing tests. Based on the methodology review and the current experimental study results, it is recommended that future ice adhesion studies fully characterize the following: the apparatuses for shear measurement, which include protocols and procedures used; the surface chemistry and roughness; the thermal conditions of the air, water, and surface; and for impact ice, the droplet conditions such as velocity and size in order to ensure repeatability within a study and comparison across studies. [ABSTRACT FROM AUTHOR]

A comprehensive review of all relevant experimental data was completed, including recent data for the drag coefficient for a sphere in supersonic and hypersonic flows. The primary characterization parameter included the relative Mach, Knudsen, and Reynolds numbers based on the relative velocity, the sphere diameter, and other parameters. This review of data showed that the previously proposed nexus at a Reynolds number below 45 was not strictly met, and it instead included a weak transonic bump, which was identified numerically for the first time with the present simulations. New continuum-gas and rarefied-gas simulations were conducted and were combined with the expanded experimental dataset to improve the quantitative description of the drag coefficient in this region. The results indicated that a quasi nexus bridges the rarefaction regime and the compressible flow regimes. The comprehensive dataset was then used to develop new empirical models for the drag coefficient that showed improved robustness and accuracy as compared to previous models. These models are limited by the critical Reynolds number associated with boundary-layer transition on the sphere, which was found to increase substantially with the sphere Mach number. [ABSTRACT FROM AUTHOR]