Abstract
To simulate aircraft thermal anti-icing systems and solve the conjugate heat transfer of air-droplet flow and solid skin, the heat and mass transfer model of the runback water on the anti-icing surface was combined with the heat conduction equation of the skin by loosely coupled methods. According to the boundary conditions used for the runback water conservation equations, two loose-coupling methods for the heat exchange between the runback water and the solid skin were developed based on surface heat flow and surface temperature, respectively. The anti-icing and ice accretion results of a NACA 0012 electro-thermal anti-icing system were obtained by the two loose-coupling methods. The heat flow-based method directly solves the thermodynamic model of the runback water without any extra assumptions, but the convergence rate is relatively slow. On the other hand, the temperature-based method achieves higher calculation speed, but the freezing point is extended to an artificial temperature range between water and ice phases. When the value of the artificial temperature range is small, the results obtained by the temperature-based method are consistent with those of the heat flow-based method, indicating that the effect of freezing point extension can be ignored for thermal anti-icing simulation. Furthermore, the solutions of the two methods are in acceptable and comparable agreement with the experimental and simulative results in the literature, confirming their feasibility and effectiveness. In addition, it is found that the ice thicknesses and ice shapes rise obviously near the runback water limits as a result of the transverse heat conduction of the solid skin.
Highlights
When an aircraft flies in the cloud under icing conditions, its windward surfaces collect super-cooled water droplets, and ice accretion may occur [1]
Since the effects of surface temperature and ice shape on external air flow and water droplet impact can be neglected, the convective heat transfer coefficient is assumed unchanged during the iteration process [11], and the anti-icing simulation is reduced to the coupled analysis of the runback water thermodynamics and the internal heat conduction
Due to the parameters offered to the heat and mass transfer equations of the runback water, the two loose-coupling methods below were developed with different solution procedures
Summary
When an aircraft flies in the cloud under icing conditions, its windward surfaces collect super-cooled water droplets, and ice accretion may occur [1]. To predict the temperature distribution on the anti-icing surface and analyze the system performances, a coupling method is necessary for the conjugate heat transfer of the external air flow, the internal skin heat conduction and the thermodynamics of the runback water on the aircraft surface. Since the effects of surface temperature and ice shape on external air flow and water droplet impact can be neglected, the convective heat transfer coefficient is assumed unchanged during the iteration process [11], and the anti-icing simulation is reduced to the coupled analysis of the runback water thermodynamics and the internal heat conduction. The coupling methods are critical for thermal anti-icing simulations to ensure the convergence of both temperature and heat flow at the runback water film-solid interface. According to the parameters transferred between the water film and solid domains, various approaches, with different computational stabilities and convergences, have been established to implement the heat flow-based method for thermal anti-icing simulations. One should be the parameter provided by the adjacent solid skin domain, and the other is the constraint between the freezing point and the phase state of runback water
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