Comparison of Transport Properties Models for Flowfield Simulations of Ablative Heat Shields

The goal of this study is to evaluate the effects of different models for calculating the mixture transport properties on flowfield predictions of ablative heat shields. The Stardust sample return capsule at four different trajectory conditions is used as a representative environment for Earth entry. In the first part of the study, the results predicted using Wilke's missing rule, with species viscosities calculated using Blottner's curve fits and species thermal conductivities determined using Eucken's relation, are compared to the results obtained using Gupta's mixing rule with collision cross-section data. The heat transfer to the vehicle predicted using the Wilke/Blottner/Eucken model is found to be larger than the value obtained using the Gupta/collision cross-section model by as much as 60%. The Wilke/Blottner/Eucken model also produces a larger mass blowing rate due to the oxidation of bulk carbon by as much as 25% compared to the Gupta/collision cross-section model. In the second part of the study, the effects of the mass diffusion model are assessed using the Fick's, modified Fick's, self-consistent effective binary diffusion, and Stefan-Maxwell models. The results show that the flowfield properties calculated using the modified Fick's, self-consistent effective binary diffusion, and Stefan-Maxwell models are in good agreement. However, the Fick's model produces a larger heat transfer and mass blowing rate compared to the other diffusion models by as much as 20%.