Molten Liquid Layer Oscillation Analysis of SiO2f/SiO2 Composite under Arc-Jet Environments

This paper is devoted to the theoretical analysis of the molten liquid layer oscillation phenomenon in a SiO2f/SiO2 composite plate model under arc-jet environments. The physical model can be abstracted into a problem of a weak viscoelastic liquid film with a moderate Reynolds number flowing under the effects of constant external air-flow shear and gravity. A set of evolution equations was presented based on integral theory. The results show that both the constant external air-flow shear and viscoelasticity can destabilize the liquid film, and the effect of the external air-flow shear is much more evident. When the friction of the external air-flow shear exceeds certain thresholds, high-frequency fluctuations become markedly drastic. Alternatively, to preliminarily investigate the wave generation mechanism, constant initial and boundary conditions are applied. The results show that no wave generation occurred under constant initial boundary conditions and zero air friction. However, when air friction is present, waves are generated, and wave instability increases with air-flow shear. Thus, while viscoelasticity increases the instability of the liquid film, it is not the cause of wave generation; rather, external air-flow shear is responsible for wave generation and significantly enhances instability. Furthermore, the simulated variation trend of wave frequency along the streamwise direction coincides with the results of the arc-jet experiment. With the imposed periodic perturbation at the inlet and the initially imposed perturbation wave, it can be concluded that both air-flow shear and viscoelasticity increase the traveling speed of the waveform, and larger air-flow shear and viscoelasticity lead to greater oscillations and reduced amplitude, and capillary number, which equals bigger surface tension, can suppress fluctuation. Additionally, the Reynolds number also influences the wave-transfer velocity, which increases with a smaller Reynolds number.