Thermal ablation and radiation modeling of meteor phenomena

Meteoroids provide Earth’s primary source of extraterrestrial materials from the various nebular and planetary environments of the Solar System and beyond. These naturally delivered samples bring 50 to 100 tons of material daily. A community of researchers devotes themselves to study meteors. Their interest lies in a quest for answers in aeronomy, astronomy, geophysics, and planetology. The understanding of meteor phenomena usually derives from the correlation between observations and simplified models. However, these models lump most of the physics, incapacitating an in-depth comprehension. For instance, the Chelyabinsk event in 2013 raised awareness within the scientific community and urged them to improve the legacy models. Meteor phenomena are complex since they involve many physical aspects, such as multi-phase and non-equilibrium flows. Up to date, the most detailed simulations are incapable of coping with all these physical features. This thesis aims to build models that accurately describe a meteoroid entry and compare the results obtained with observations. We leverage engineering models developed for reentry space vehicles and extend them to meteoroid applications. We focus first on the flow analysis – high-temperature effects and radiation – and then on the material – evaporation and shear ablation. These models are valid within the continuum regime, meaning that they can be employed to derive flow characteristics of fireballs and to study bolide ablation. Chapter 2 presents state-of-the-art physico-chemical models relevant to meteoroid entry conditions. We review the necessary data to compute the metallic species thermochemical properties. These data are essential to understand the flow features and strengthen the accuracy of the meteor ablation description. We integrate the required metals data into the open-source Mutation++ library, which is coupled to a Computational Fluid Dynamics solver to provide thermochemical closure to the governing equations. In Chapter 3, we improve the engineering-based models to study meteoroid degradation and develop kinetic based evaporation models. The former models consider chemical equilibrium at the gas/liquid interface, whereas the latter account for chemical non-equilibrium and rarefied gas effects due to the presence of the Knudsen layer. We observe a significant deviation between both models under strong evaporation conditions and a considerable temperature jump at the interface due to rarefied effects. The high heating load on the meteoroid during entry leads to a phase-change of the material. As the material melts, the aerodynamic forces drive the removal of the molten layer. This behavior was observed on several ground experiments based on real meteorite samples. In Chapter 4, we apply an enthalpy method and solve the material thermal behavior to study the phase-transition phenomenon. We extend a shear ablation model developed for glass materials to meteoroids. We make a comparison between the results obtained with our models and the experiments carried out at NASA Ames Research Center on a Tamdakht H5 ordinary chondrite. For those conditions, our results show that evaporation is negligible compared to the molten layer removal. The presence of alkali metals in the flow, due to the evaporation, causes the bright light that observed during a meteor entry. This light is owed to the radiation of the chemical species within the flow. Coupling the flow field with thermal radiation is a complicated task due to the inherent high computational cost. In this work, we employ the Hybrid Statistical Narrow-Band model, which is accurate and efficient in previous studies for the reentry of space vehicles. In Chapter 5, we compare the spectral measurements carried out in the VKI Plasmatron with the numerical results and observe a good agreement between the spectral measurements and the simulated spectra regarding the emission of Fe and K. Unfortunately, it is not possible to analyze the Na intensity due to a spectral saturation from the experiment. Chapter 6 combines all the models developed in the previous chapters to study the Lost City bolide event. We couple radiation, flow, and evaporation to reproduce the luminosity at different altitudes. The numerical outcome is compared with the observations; a good agreement is found. The simulated spectra lack the presence of refractory element Ca, which is usually detected during meteor entry. We suspect that the presence of Ca results from droplet evaporation sheared away from the main body. The coupling between the flow and material suggests that the primary source of material degradation is due to the removal of the molten layer, for most of the trajectory. Below a certain altitude, radiative heating increases substantially, leading to more substantial evaporation. This analysis is made only in a small segment of the trajectory due to the complexity inherent to the coupling. In this work, we could shift from the 0D correlations or legacy models to predictive engineering models, allowing us to describe meteor phenomena in fair agreement with the observations. The outcome of this thesis can also be applied to study man-made space debris degradation in Earth’s atmosphere, in particular, to detect their radiative signature during reentry phase.