Aerothermodynamic modelling of meteor entry flows in the rarefied regime

Abstract

Due to their small size and tremendous speeds, meteoroids often burn up at high altitudes, above 80 km, where the atmosphere is rarefied. Ground radio stations are able to detect the free electrons concentration in the meteoroid wake, which is produced by hyperthermal collisions of the ablated species with the free-stream. The interpretation of radio data, however, currently relies on phenomenological methods, derived under the assumption of free molecular flow, hence, poorly accounts for the dynamics of the vapour, chemistry, and diffusion in the meteor trail. In this work, we aim to provide a detailed description of the flowfield around a meteoroid by means of Direct Simulation Monte Carlo and to obtain the evolution of the free electrons in the meteor wake via an extended trail simulation. An evaporation boundary condition is developed in the framework of an open source DSMC software. The material is assumed to be composed by a mixture of metal oxides which are typically present in ordinary chondritic meteorites. The transport properties of the ablated vapour are computed following the Chapman-Enskog theory and the DSMC phenomenological parameters are retrieved by fitting the collision integrals over a wide range of temperatures. As a last step, chemical and diffusion processes in the trail are computed. Starting from the baseline DSMC solution, our approach marches in time along the precomputed streamlines, calculating chemistry and radial diffusion for metals and free electrons. As study case, the flow around a 1 mm evaporating meteoroid is analysed at different altitudes. A high level of thermal nonequilibrium is appreciated in the head of the meteor, whereas in the trail, after a few diameters, the flow equilibrates. At lower densities, the vapour can travel upstream without interacting much with the incoming jet. On the other hand, at lower altitudes, re-condensation plays a significant role in the stagnation region. Finally, a trail, several meters long and formed by metallic species, generates behind the body. Ionization of sodium turns out to be the dominant process in the production of free electrons, whereas radial diffusion seems to prevail over recombination as depletion mechanism.

Lagrangian diffusive reactor for detailed thermochemical computations of plasma flows

“…62,63 Extended trail simulations of meteors is an ongoing work performed by means of the Lagrangian solver, including ablation products. 64 where the source term for the electron heavyparticle translational energy transfer and chemistryenergy coupling is introduced as follows, 44 where P = − (i,j)∈S BB Λ ij (h f j −h f i )n j A ji expresses energy lost through bound-bound transitions from an upper electronic energy level j of argon to a lower level i, denoted by the set S BB , with the escape factors assumed to be Λ ij = 0 for transitions to the ground state (optically thick) and 1 for all the others (optically thin); and A ji the Einstein coefficient for the transition. The term P e = i∈S31 (h f Ar + − h f i )n i R i −1.42 ×…”

“…62,63 Extended trail simulations of meteors is an ongoing work performed by means of the Lagrangian including ablation products. 64 where the source term for the electron heavyparticle translational energy transfer and chemistryenergy coupling is introduced as follows, 44 Ω e = ρ e [e T e (T ) − e T e (T e )]/τ ET + r∈R ∆h r τ r + e t e ω e . The set R ⊂ R comprises the electron-impact ionization and excitation reactions.…”

“…The calculation of the free electron concentration in hypersonic trails was also discussed in this paper, which can easily be applied to the fields of telecommunication blackout and the radio-detection of meteors during atmospheric entry [64,65]. Extended trail simulations of meteors is an ongoing work performed by means of the Lagrangian solver, including ablation products [54]. where k is the index of streamline considered.…”

“…, where quantity α is a non-negative constant. The Lagrangian reactor could retrieve the analytical solution up to numerical precision [54].…”

Study of Iron and Stony Meteorite Ablation Based on Simulation Experiments in an Arc Heater

“…Comprehensive data on the ablation process, surface temperature, and surface morphology after ablation have been obtained in several experiments (Bronshten 1983). Numerical models have been established to predict ablation (Johnston & Stern 2017;Bariselli et al 2018). Recently, using advanced measurement techniques and employing the powerful simulation capabilities of novel test facilities, simulation tests have been conducted for several meteorite materials.…”