Ablation evolution of a new light weight silicon based thermal protection material in high temperature gas flow

High silicon oxygen/phenolic aldehyde (VSF/PR) ablative heat-proof material is widely used as resin-based heatproof system for long-term aircraft. Understanding the generation and flow process of the surface droplets during high temperature is key to improving the thermal stability, and prior to which, a direct visualization of the surface evolution is required. Here we use optical imaging technique to in-situ and real time record the surface evolution of a flat plate subjected to thermal ablation at 1700 degrees C in wind tunnel. Based on the experimental results processed using image processing method and by combining the fluid theory in high temperature wind tunnel, we explained the distribution of the surface temperature and surface liquid droplets, the velocity field, and the movement of the liquid droplets on the plate surface. Results show that the distribution of the liquid droplets was correlated to the temperature distribution. A verification experiment for the merging process of two liquid droplets shows that droplet with high viscosity would generate a great friction force and cause the droplet to move forward in a rolling manner. The chasing and merging process of the liquid droplets with high viscosity is rather an entrainment process than a spontaneous merging process normally induced by surface tension. These findings help to understand the flow behavior of the liquid droplets during thermal ablation.

Automated summary

In this study, the surface evolution of liquid droplets at high temperatures on a flat plate was recorded in situ and in real time using optical imaging technique. By combining fluid theory in high temperature wind tunnel, the relationship between surface temperature and droplet distribution, as well as the merging process of high viscosity droplets were explained. The findings suggest that the behavior of high viscosity liquid droplets during thermal ablation is more of an entrainment process rather than a spontaneous merging process induced by surface tension.