Collaborative research center 1667 ATLAS
At VLEO altitudes, the atmosphere is rarefied but still dense enough to affect satellite operations. The primary atmospheric constituent at these altitudes is atomic oxygen. These particles interact with the satellite’s surface, which leads to Drag, surface erosion and thermal effects.
Direct Simulation Monte Carlo (DSMC) is a computational method used to model gas flows in rarefied conditions, such as those found in VLEO. It provides accurate models of gas-surface interactions, helping engineers design more resilient and efficient satellites.
This project is part of the Collaborative Research Centre (CRC) 1667 “Advancing Technologies of Very Low Altitude Satellites (ATLAS)”.
Gas-Surface-Interaction Mechanisms
The most common scattering models in DSMC are the Maxwell and Cercignani-Lampis-Lord (CLL) models.
- The Maxwell model assumes that gas particles striking a surface can either be specularly reflected or diffusely reflected with a certain probability.
- The CLL model provides a more detailed representation by considering the accommodation coefficients for both tangential and normal momentum components. As a result, it can take into account quasi-specular reflections and allows a more realistic simulation.
However, realistic accommodation coefficents used as input to these models are not available for virtually any material. In addition, these coefficents are dependent on surface roughness, temperature, impact angle, velocity etc..
Atomic oxygen (AO) plays a significant role as a chemically active radical in the flow conditions of VLEO. It is known that AO deposits on the surfaces of the satellite which naturally also changes the reflection behaviour of the surface and thus may strongly change the properties of the wall interaction towards a more diffuse scattering.
To date, there has been little work looking at surface reactions in DSMC simulations in VLEO.
Advanced GSI-Model in VLEO
Given the aforementioned limitations in GSI modeling, optimizing a satellite has become nearly impossible due to insufficient modeling and the heavy reliance on uncertain input parameters such as accommodation coefficients.
Therefore, this project seeks to utilize microscopic data from molecular dynamics simulations to develop and incorporate a more detailed gas-surface interaction model into DSMC simulations. This will be done in close collaboration with ATLAS Project A01, which focuses on simulating interactions between atomic oxygen and metals at the atomistic level.
The use of molecular dynamics scattering data and data-driven approaches for modeling gas-surface scattering in DSMC simulations marks a significant improvement over traditional scattering methods. By employing techniques like the Distribution Element Tree Method or Machine Learning-Based Models (like the Gaussian Mixture Model), it is possible to achieve more accurate and efficient simulations.
Extensions of the GSI-Model within the DSMC method will be developed and implemented to facilitate surface reactions such as adsorption, desorption, Eley-Rideal, and Langmuir-Hinshelwood reactions. Rate coefficients from Project A01 will be utilized for this purpose. Subsequently, a more detailed chemistry model for the surfaces will be developed, which functions similarly to a coarse-grained lattice kinetic Monte Carlo model.
Contact
Miklas Schütte
M.Sc.Research Associate
