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Ice accretion is a purely unsteady phenomenon that is presently approximated by most icing codes using quasi-steady modeling. The accuracy of ice prediction is thus directly related to the arbitrarily prescribed time span during which the impact of ice growth on both flow and droplets is neglected. The objective of this work is to remove this limitation by implementing a cost-effective unsteady approach. This is done by fully coupling, in time, a diphasic flow (interacting air and droplet particles) with the ice accretion model. The two-phase flow is solved using the Navier-Stokes and Eulerian droplet equations with dual-time stepping in order to improve computational time. The ice shape is either obtained from the conservation of mass and energy within a thin film layer for glaze and mixed icing conditions, or from a mass balance between water droplets impingement and mass flux of ice for rime icing conditions. The iced surface being constantly displaced in time, Arbitrary Lagrangian-Eulerian terms are added to the governing equations to account for mesh movement. Moreover, surface smoothing techniques are developed to prevent degradation of the iced-surface geometric discretization. For rime ice, the numerical results clearly show that the new full unsteady modeling improves the accuracy of ice prediction, compared to the quasi-steady approach, while in addition ensuring time span independence. The applicability of the unsteady icing model for predicting glaze ice accretion is also demonstrated by coupling the diphasic model to the Shallow Water Icing Model. A more rigorous analysis reveals that this model requires the implementation of local surface roughness and that previous quasi-steady validations cannot be carried out using a small number of shots, therefore the need for unsteady simulation.

Even though the power of supercomputers has increased extraordinarily, there is still an insatiable need for more advanced multi-disciplinary CFD simulations in the aircraft analysis and design fields. A particular current interest is in the realistic three-dimensional fully viscous turbulent flow simulation of the highly non-linear aspects of aero-icing. This highly complex simulation is still computationally too demanding in industry, especially when several runs, such as parametric studies, are needed. In order to make such compute-intensive simulations more affordable, this work presents a reduced order modeling approach, based on the "Proper Orthogonal Decomposition", (POD), method to predict a wider swath of flow fields and ice shapes based on a limited number of "snapshots" obtained from complete high-fidelity CFD computations. The procedure of the POD approach is to first decompose the fields into modes, using a limited number of full-calculations snapshots, and then to reconstruct the field and/or ice shapes using those decomposed modes for other conditions, leading to reduced order calculations. The use of the POD technique drastically reduces the computational cost and can provide a more complete map of the performance degradation of an iced aircraft over a wide range of flight and weather conditions.

A detailed study is proposed for understanding the use of aircraft deicing and anti-icing fluids (ADAF) and optimal use of these fluids in airport operations. A detailed literature review of past and current technologies is conducted and possible opportunities to improve the use of ADAF and relevant recommendations are derived. Mathematical optimization models (e.g. MINLP with binary variables) based on a variety of objectives, which deal with exhaustive sets of system constraints are formulated, developed and applied to case studies. One real-life case study area which routinely carries out aircraft deicing is used for testing the mathematical optimization formulations for optimal use of fluids under budgetary and environmental compliance constraints. Based on the recommendations from one of the best optimization model formulations it is hoped that it will be used for a real-time implementation. Results from these formulations show the models to be robust and applicable. / by Scott E. Ornitz. / Thesis (M.S.C.S.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.

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