Pioneer Venus Large Probe Stagnation Point Entry Heating with Coupled Ablation

The objective of this work is to reconstruct thermocouple temperature measurements taken at the stagnation point of the Pioneer Venus large probe using uncoupled and coupled ablation calculations. The time history of the large-probe forebody entry heating was obtained from a trajectory-based analysis that employed a material response solver to model equilibrium and finite-rate ablation chemistry at the surface. For the uncoupled approach, equilibrium ablation chemistry was assumed in the material response calculations, but the material response outputs were not returned to the flowfield solver. Therefore, the effects of char and pyrolysis gas injection into the boundary layer due to ablation (e.g., convective blockage and radiative energy absorption) did not influence the flowfield solutions. For the coupled approach, finite-rate ablation chemistry was modeled, and the material response outputs were returned to the flowfield solver. Therefore, the effects of char and pyrolysis gas injection into the boundary layer were included in the flowfield solutions. The effects of modeling uncoupled and coupled ablation on the stagnation-point heating environment are described. The reconstructed thermocouple temperatures from the two ablation approaches are within 10% of the flight measurements throughout the entry heat pulse, but the coupled results compare more favorably with the measurements. The reconstructed temperatures in this work are improved results compared to prior reconstructions for the large probe.