Experimental and numerical studies of spallation particles ejected from a light-weight ablator

During atmospheric entry, thermal protection material (ablator) is strongly heated by aerodynamic heating. Due to this fact, micro-order particles are generated and ejected from an ablator surface, which is called 'Spallation'. In the previous ground experiments in an arc-heated facility, the presence of spalled solid particles has been confirmed upstream of a detached shock wave or a stagnation-point boundary layer. Spallation phenomena are considered to be a possible cause of increasing heat-transfer rates on an ablator surface in the downstream region. To estimate the effect of a spalled particle on an ablator, correct values of particle parameters (e.g., size, flight velocity, position) are needed. Therefore, we carried out the heating experiment for a trial manufactured light-weight ablator, and then detailed parameters for each particle were analyzed directly from the visualized pictures. As for the visualization method, the in-line holography method, that uses a recorded hologram pattern appearing behind of an illuminated particle by a collimated laser beam, was applied to evaluate the particle parameters. Moreover, the flight path of a single spallation particle was also numerically analyzed in the present study. As a result, some particles ejected from an ablator surface were visualized in the upstream region and their parameters were evaluated successfully. This fact indicates the availability of the in-line holography method for evaluation of spallation-particle parameters. By using the obtained particle parameters, the effect of a spalled particle on an ablator surface was estimated.