The hybrid NS-DSMC method will be used to simulate the lateral jet interaction flow of a RACS system with the rarefied atmosphere in transitional regimes. The open-source DSMC solver under the framework of OpenFOAM, used to solve the rarefied zone of the flow field, will be coupled with an in-house, compressible, finite-volume, structured NS solver that will be used to solve the continuum regime zones of the flow field. The coupling of the two solvers will be accomplished with a state-based method, which implies an exchange of information between a continuum-molecular overlap region. The location of this region will be intercepted and tracked through the local Knudsen number based on the gradients local length (GLL). A campaign of 2D numerical simulations for a lateral Hydrazine (HZ) RACS thruster expanding at high altitude will be carried out with various molecule models (VHS and VSS) to investigate the effect of collisions between the particles and non-equilibrium effects. The results will be used to set up and initialize a campaign of 3D numerical simulations that will be used to highlight the three-dimensional effects of the phenomena under investigation, to shed some light on the complex physical mechanisms that characterize the interaction of the nozzle plume with the rarefied atmosphere, and to study the effects of chemical reactions, vibrational and electronic excitation of the air molecules in the rarefied regimes.
The present project aims to advance the knowledge of RACS thruster plume expanding into a highly rarefied atmosphere to:
1) Characterize the degree of rarefaction and the plume expansion as the altitude increase;
2) Analyze eventual backflow that could hamper the accomplishment of the mission through deposition of particles on the surface of optical instruments and sensors;
3) Analyze the force and torque disturbance generated by the impingement of the plume on the payload surface and the heating of sensitive surfaces.
This will lead to the clarification of the role of the degree of rarefaction, nozzle characteristics, and the type of propellant chosen for these kinds of engines.
A side benefit of this project is the development of a numerical hybrid NS-DSMC solver to perform simulations of these kinds of flows. The outcomes are expected to have a strong impact from the viewpoint of both fundamental science and engineering, bringing advances to a critical research area in the space field and constituting a resource for researchers involved in the study of rarefied flows and improvement of RACS technologies.