Survey of convective blockage for planetary entries

During a planetary entry, the decomposition of the thermal protection system material resin by the pyrolysis process produces strong blowing gases that are injected into the boundary layer. Induced by the blowing gas, the blockage phenomenon has a strong effect on the level of heat-fluxes. For some entries, such as Earth super-orbital re-entries characteristic of sample return missions, blockage is one of the key issues that have to be addressed. Additionally, this phenomenon is strongly linked to turbulence and to the porous aspects of the ablative material. Here, experimental, numerical and flight data available for different missions, involving high level of heat-fluxes, are gathered and discussed. The models for convective blockage found in the literature have been reviewed in order to select a generic way to estimate this phenomenon. It appears from this study that the convective blockage is still not fully understood and that there is no established approach for its accurate modelling since most of the existing correlations possess a high degree of empiricism.

► Survey of experimental, numerical and flight data related to convective blockage for planetary entry.
► Survey of several missions: Galileo, Pioneer-Venus, Apollo, Stardust, Genesis, Hayabusa and Russian missions.
► Review of available models and discussion for convective blockage factor and blowing of pyrolysis gases.
► Interaction of pyrolysis gases with char material as porous media, and with boundary layer turbulence