Unified Kinetic Approach for Simulations of Gas Flows in Rarefied and Continuum Regimes

During trans-atmospheric flight, a spacecraft passes through both rarefied and continuum flow regimes, which are often described by different physical models. This project aims to develop a unified computer code that can automatically switch betweenkinetic and continuum models while maximizing computational efficiency and ensuring numerical stability. The efficiency of the method will be attained by using similar computational techniques for kinetic and continuum solvers, and employing intelligentdomain decomposition algorithms. Direct Numerical Solvers (DNS) of the Boltzmann transport equation (BTE) will be adopted for description of multi-dimensional flows at moderate and low Knudsen numbers. DNS allows the BTE to be solved using spatiallynon-uniform computational grids. In the Knudsen layers, the grid size is smaller than the characteristic mean free path while in the continuum domains it is much larger than the mean free path. DNS offers unique advantages compared to DSMC methods whichrequire computational cells smaller than the mean free path even in the continuum flow domains. Kinetic schemes of gas dynamics will be used to facilitate the automatic domain decomposition and coupling of BTE with Navier Stokes or Euler equations. Theadvantages of this new methodology will be demonstrated by comparison against more traditional approaches. The computational tool that results from this work would be a significant advancement in reliable and efficient modeling techniques fortrans-atmospheric flight. It could be used by both government and industry researchers to help design and analyze trans-atmospheric vehicles, new micro-propulsion systems, plumes, etc. Besides aerospace applications, the software will find numerousapplications for several