Effect of Characteristic Phenomena and Temperature on Super-Cooled Large Droplet Icing on NACA0012 Airfoil and Axial Fan Blade

Icing simulations involving super-cooled large droplets (SLDs) on a NACA0012 airfoil and a commercial axial fan were performed considering the characteristic behavior of SLD icing (i.e., splash-bounce, deformation, and breakup). The simulations were performed considering weak coupling between flow field and droplet motion. The flow field was computed using the Eulerian method, wherein the droplet motion was simulated via the Lagrangian method. To represent the ice shape, an extended Messinger model was used for thermodynamic computation. The ice shape and collection efficiency of the NACA0012 airfoil derived using the icing simulation exhibited a reasonable agreement with the existing experimental data. The icing simulation results for the axial fan, in terms of distribution of ice on the blade and its influence on the flow field, indicated that flow separation occurred, and the mass flow rate of the flow passage decreased. Moreover, the splash and bounce phenomena considerably influenced the icing process; however, the effect of the deformation and breakup phenomena was negligibly small. In terms of the effect of the SLDs on the icing phenomena, it was noted that, with the decrease in the SLD temperature (from −5 °C to −15 °C), the number of adhering SLDs increased, whereas the number of splashing and bouncing SLDs decreased.

Effect of Chemical Vapor Deposition Process Parameters on Graded SiC-SiO2 Coating

The effect of the chemical vapor deposition (CVD) process parameters on the structure of graded SiC-SiO2coating was studied through thermodynamic computation. The addition of enough hydrogen into the carrier gas is necessary for the synthesis of the graded SiC-SiO2coating. Both high deposition temperature and low deposition temperature make the change of the composition of the coating abrupt with the change of the composition of CVD atmosphere, which is harmful to the process control of the coating. A low concentration of reactants is preferred according to the thermodynamic computation but the deposition rate is too low at a low concentration of reactants. When hydrogen is the carrier gas and the concentration of SiCl4is between 1 – 2 vol%, the graded SiC-SiO2coating with a suitably graded distribution of SiC and SiO2can be easily obtained through gradually changing the flow rate ratio of methane and water vapor at 1100 - 1200 °C.