CC BY 4.0Schwarz, JohannesJohannesSchwarzAxelsson, KristjanKristjanAxelssonAnheuer, DanielDanielAnheuerRichter, MartinMartinRichterAdam, JohannaJohannaAdamHeinrich, MartinMartinHeinrichSchwarze, RüdigerRüdigerSchwarze2023-05-032023-05-032023https://publica.fraunhofer.de/handle/publica/441288https://doi.org/10.24406/publica-129810.1016/j.softx.2023.10137810.24406/publica-1298Classical continuum methods fail in predicting gas flows with higher Knudsen numbers. Several models have been derived in the past which extend the classical Navier-Stokes equations (CNSE) in order to capture the particle character of the medium. One approach takes into account the kinetic theory of gases. Accordingly, an additional self-diffusive mass flux can occur, which is a result of strong temperature and pressure gradients. These effects led to the derivation of the so called extended Navier-Stokes equations (ENSE). Under rare conditions they can be treated analytically. However, in most cases numerical methods are necessary. Usually the Finite-Volume-Method is utilized for numerically solving the CNSE, which is why the present work uses the well-known open-source-tool OpenFOAM as a foundation for developing an ENSE solver. It is pointed out that the advantage of being able to discretize certain terms implicitly and define additional diffusion face-flux fields leads to a huge performance gain in this case. Using a simple microchannel test case, the results are verified against analytical formulas.enExtended Navier-Stokes equationsOpenFOAM solverComputational fluid dynamicsMicrochannel flowDDC::500 Naturwissenschaften und Mathematikjournal article