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Section: New Results

Kinetic modelling of rarefied gases and space reentry

  • Participants: Giorgio Martalò, Luc Mieussens, Julien Mathiaud

  • Corresponding member: Luc Mieussens

After the end of the post-doc of Giorgio Martalò, a paper has been published [2], in which as presented the derivation of modified boundary conditions for the compressible Navier-Stokes equations to take into account rarefied flow effects. Another paper, related to some numerical aspects, should be submitted soon. Moreover, a paper written by J. Mathiaud and L. Mieussens [7]. This is an extension of their previous work on the modelling of collisions in gases by Fokker-Planck model to polyatomic gases.

Finally, Baranger et. al [53] have presented a way to obtain correct numerical boundary conditions for the approximation of the Boltzmann equation to take into account collisions of gas molecules with solid boundaries. Standard second order finite volume schemes degenerate to first order close to solid walls, but it has been shown in [53] that a suitable use of extrapolation and slope limiters can give second order accuracy. This greatly improves the computation of the heat flux on solid boundaries for atmospheric re-entry flow simulation, for instance.

Finally, the project of numerical and physical modelling of the liquid ablation (for atmospheric re-entry flows) has been concluded by the defense of Simon Peluchon in November 2017. So far, one paper has been published on this subject [8], but at least another one should be submitted soon. Note that Simon Peluchon will be hired in the CEA as a researcher-engineer in January 2018. This subject might induce new collaborations between the CEA and Cardamom, in particular for the use of unstructured grids.

We have developed some activities concerning the application of UQ analysis to aerospace problems. First, we have illustrated in [44] how to perform a Bayesian calibration of the free stream parameters of a hypersonic high-enthalpy flow around a cylinder, exploiting active subspaces for the reduction of the dimensionality of the input space. The configuration taken into account was the HEG I configuration, known in literature as a validation test-case for hypersonic CFD. The goal of the Bayesian inversion was to show the feasibility in using measurements of pressure and heat flux at the stagnation point for rebuilding freestream velocity and density.

Then, we have realized several studies concerning ablation and the characterization of ablative materials. In particular, in [16] and [15], we have illustrated a proof-of-concept of the coupling between a thermo-chemical ablation model and modern uncertainty quantification techniques with the aim of rebuilding the ablative material tests performed in the inductively coupled Plasmatron facility at the von Karman Institute. Finally, in [14], we have shown how an approach that uses uncertainty quantification methodology can be used in order to rigorously compute error bars on numerically rebuilt values of enthalpy and catalycity from the Plasmatron facility.