Speaker
Description
One of the peculiarities of some space debris materials compared to thermal protection systems is that the ablation of the critical parts of such objects might involve melting and the presence of three phases (gas, liquid, solid). This is the case for glassy and metallic materials. Given the huge properties differences that exist between the gas and the condensed phases and the complex interactions occurring at the interface, the study of this kind of situation is particularly challenging from a numerical point of view.
To complement the available low-fidelity engineering tools, we have been developing at Cenaero two main strategies inside our in-house high-order multiphysics platform, named Argo, based on the discontinuous Galerkin spatial discretization of the governing equations. The first one relies on a loosely-coupled approach in which the gas and the material solvers exchange information across a boundary in a staggered manner. The second approach considers a strongly coupled formulation of the problem by means of a monolithic sharp interface solver in which interface jumps conditions are enforced.
In the framework of the GSTP activity “Validation of Space Debris Demise Tools Using Plasma Wind Tunnel Testing and Numerical Tools” (led by the von Karman Institute), we applied the staggered approach to reproduce ablation experiments on silicate (quartz and Zerodur®) and titanium samples, conducted in the Plasmatron facility of the von Karman Institute. The multispecies reactive gas solver provides to the material solver the shear stress, the heat flux and the pressure at steady state. In the energy balance at the interface, evaporation and re-radiation are also taken into account. The mass balance is exploited to compute the recession velocity of the interface, which is treated as a moving immersed boundary (i.e. unfitted to the underlying mesh). Inside the material volume, enthalpy absorption during the melting process is modeled and the velocity from the liquid to the solid regions is penalized by a Darcy term. On the other hand, the material solver gives the interface temperature to the fluid solver that iterates until steady-state is reached. Exchanges between both solvers are performed at predefined times based on the expected material response.
Comparisons to experimental results revealed that catalytic effects must also be taken into account for silicate materials while passive and active oxidation dominate for titanium in air environment. Finally, shock capturing capabilities have been added to the code such that experiments in supersonic conditions could also be reproduced.
This presentation will cover the modeling and numerical aspects of the staggered and monolithic strategies as well as their application to experimental configurations.
