# Parameter Study for the Ice Adhesion Centrifuge Test
## 2 Materials and Methods
Roughness data \(\mathrm{R_{a}}\) (arithmetic average value of the roughness profile) and \(\mathrm{R_{z}}\) (maximum height of the profile) were determined using a Perthometer M2 (Mahr GmbH, Gottingen, Germany). The four selected materials represent a reasonable range of wettability and roughness properties (from smooth to rough and hydrophilic to hydrophobic). Surface parameters are expressed in Table 2 as the means of 6 measurements from 3 test samples. Tests started 21 days after coating application, at the earliest. Prior to each test, samples were cleaned using isopropanol and soft tissue. Between the tests, samples were stored in a dry and dark environment at room temperature. Ice adhesion centrifuge tests were conducted in the Fraunhofer IFAM ice lab with an integrated ice wind tunnel (Figure 1). The ambient temperature during the ice formation and adhesion tests was kept constant at \(-8\)\(\,{}^{\circ}\mathrm{C}\). This temperature was selected as it is low enough to prevent unstable icing conditions (these may occur close to 0 \(\,{}^{\circ}\mathrm{C}\)). Additionally, at \(-8\)\(\,{}^{\circ}\mathrm{C}\), different ice types can form in the ice wind tunnel, depending on the air velocity. Prior to the ice formation process, test samples were pre-conditioned to this test temperature. Four different scenarios were defined for the assessment of the ice adhesion depending on the ice types and velocities (Table 3). Static ice was produced by inserting each test sample into a silicone mold that allowed defined ice formation in the required area (Figure 2a). Three milliliters of de-ionized water were filled into the mold and allowed to freeze onto the test surface. After 90 min, the silicone mold was removed, and the sample was stored for a minimum of 15 min at the test temperature without any mechanical disturbance prior to the installation into the centrifuge. Figure 1: View inside the Fraunhofer IFAM ice lab (**a**) and scheme of the closed-loop ice wind tunnel (**b**) with a fan drive system (1), turning vanes (2), heat exchanger of refrigeration system (3), humiditystat (4), water spray bar (5), water reservoir and pumps (6), test section entrance (7), test section (8), and diffusor (9). For impact ice, the pre-conditioned test sample was mounted onto a custom-made sample holder that allowed the positioning of the test surface in the center of the ice wind tunnel test section for a defined time (Figure 2b). After impact ice formation, the sample was removed from the ice wind tunnel and kept in the specimen holder for 10 min at a constant temperature of \(-8\)\({}^{\circ}\)C. After disassembly from the specimen holder, the test sample was stored for an additional five minutes prior to the installation in the centrifuge for testing of the ice adhesion. The four icing scenarios resulted in the formation of different ice types and shapes (Table 4). For static ice, compact glaze ice was produced in a well-defined area. Impact ice that was produced at 40 and 60 m/s also appeared as clear glaze ice but with a rough surface. Water droplets in the ice wind tunnel section hit the surface and were frozen at the test surface rather instantly. However, the following water droplets could run over this first icing layer before freezing, resulting in ice formations also at the test sample sides (also covered with the test materials). This phenomenon was not observed for impact ice accreted at a 95 m/s wind tunnel velocity. Short freezing times led to ice growth towards the wind direction instead of ice formations at the sample sides. The ice started to develop a milky appearance and was defined as mixed ice (mixture of glaze and rime ice). For ice adhesion tests, a custom-made centrifuge with a modified rotor to place and fasten the prepared test samples was used as already described elsewhere [16]. Opposite the ice is a counterweight that can be adjusted, according to the ice mass, to reduce vibrations (see Figure 3).