The Deliverable D10.4 summarizes the activities conducted within the WP10 of the ICE-GENESIS project related to the snow numerical capabilities. Further details on the activities are given in the Deliverables D10.1 [1], D10.2 [2], D10.3 [3], including the description of the experimental, modelling and numerical activities. It is noteworthy to mention that these activities are tightly associated to those of the WP5 “Instrumentation for snow and microphysical properties” and WP7 “Snow test capability“ and have led to a fruitful collaboration with the partners involved in these WPs.

Most of the efforts in WP10 have been devoted to the transport models and, more specifically, the drag and thermal models for snow particles. On the drag part, at first, several academic experiments have been performed within ICE-GENESIS considering real and artificial snowflakes in order to get the estimation of the free fall speed. The next step consisted in assessing and down-selecting several physical models versus this experimental data, using 2D numerical solvers. This led to retaining the Hölzer-Sommerfeld model [4]. On the thermal part, the same process has been employed and the down-selection process has led to retain an adaptation of the HAIC model [5] based on the melting time of a snow particle. In any case, for these two models, the geometrical description of the snow particle is based on the oblate spheroid approximation. An additional conclusion of the work is that 2D geometrical descriptors are relevant and could be also used. Both drag and thermal models have been implemented into the 3D numerical tools and successfully assessed with respect to the experimental data and the 2D numerical results.

On the accretion part, the HAIC models concerning the sticking efficiency and the erosion have been employed and assessed versus two experiments performed within ICE-GENESIS at CSTB and RTA IWTs on a NACA0012 airfoil. A first objective has consisted in evaluating the influence of the experimental uncertainties on the experimental LWR, TWC values on the numerical results. In a second time, an optimization process has been performed, trying to define optimal values for some parameters of the HAIC sticking and erosion models. The objective function of this process was based on the ice shape. While this process has been quite successful for most of the cases, the variations of the parameters are questionable from a physical point of view. Such a fact indicates that a better modelling is required or that the objective function used for the optimization process is not adapted.

Finally, some additional experimental and modelling activities have been realized to describe the snowflake impact. A model for the break-up threshold has been proposed and matched with the HAIC model for Ice Crystals [6]. The experimental data has also conducted to propose a probability density function describing the size of the snow particles emitted after an impact.

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