Cold Soaked Fuel Frost Roughness Evolution on a Simulated Integrated Fuel Tank with Aluminum Skins

Cold soaked fuel frost (CSFF) is frost that forms on aircraft wing surfaces following a flight because of cold excess fuel remaining in integrated fuel tanks. Previous investigations by Zhang et al. (2021a) and Zhang et al. (2021b) have focused on experimental measurements and correlation development for frost observed using a small frost wind tunnel employing a thermo-electric cooler to impose a surface temperature for a range of environmental conditions. To model the CSFF approach in more detail, an experimental facility was developed and described by McClain et al. (2020) using a thermal model of an integrated wing fuel tank placed inside of a climatic chamber. In this paper, experimental measurements of CSFF are presented using two aluminum wing skins. One of the skins was created using an aluminum rib structure, and the other skin was created without the rib. An automated, photogrammetric approach was used to characterize the roughness evolution on each surface when exposed to a set of environmental conditions. The measurements were then used to explore the correlation of Zhang et al. (2021b) when considering the convection through the surrogate fuel fluid and the conduction through the aluminum skin. The correlations of Zhang et al. (2021b) capture the trends of the root-mean-square (RMS) roughness and the relative magnitudes of the RMS roughness when comparing the effect of different air temperatures on frost evolution. However, the sand-grain roughness predictions using the correlation of Zhang et al. (2021b) indicate that the present model implementation is underestimating the frost surface temperature generally leading to predictions of excessive equivalent sand-grain roughness values.