Numerical Simulation of In-flight Icing by Water Droplets with Elevated Temperature

When conducting experiments in icing wind tunnels (IWTs), a significant question is to what extent the temperature of the water droplets generated by the spray system has converged to the static air temperature when the droplets impinge on the test object. This is a particularly important issue for large droplets, since the cooling rate of droplets decreases sharply with increasing diameter. In this paper, on the one hand, realistic droplet temperature distributions in the measurement section of the Rail Tec Arsenal IWT (located in Vienna) are computed by means of a numerical code which tracks the paths of the droplets from the spraying nozzle to the measurement section and simultaneously calculates their cooling rates. On the other hand, numerical icing simulations are performed to investigate to what extent the deviation of the droplet temperature from static air temperature influences icing and thermal anti-icing processes. For this purpose, three selected cases are analyzed – two unheated cases and one heated case. Besides providing important information to the operators of Rail Tec Arsenal’s IWT (and, possibly, also other IWTs), the current research can be helpful in the layout and design process of new (vertical) IWTs operating in the regime of Supercooled Large Droplets: The approach presented in the paper can provide valuable information about the expected deviations of icing test results depending on the spatial distance between the spray system and the measurement section of the IWT being analyzed.