Implementation of thermionic emission boundary conditions in a five-moment multifluid plasma model

Abstract: Traditional expressions for the thermionic emission of electrons from hot surfaces, such as the Richardson-Dushman equation (Richardson 1924) provide only the current (equivalently, mass flux) of electrons from the surface as a function of the surface temperature and material-dependent work function. We have recently extended the theory of Young (1959) and Murphy and Good (1956) to derive additional analytical expressions for the electron normal momentum and energy fluxes from the emitting surface. Our multi-fluid plasma code, Cerberus enables simulating complex domains through the use of adaptive mesh refinement (AMR) and embedded boundaries (EB). In this paper, we describe the implementation of these thermionic electron fluxes on the embedded boundaries within a Cerberus simulation. The target application of this work is modelling of sheath structures for flow conditions where thermionic emission from hot leading edges of hypersonic vehicles may result in a significant cooling effect a process known as electron transpiration cooling (ETC). Keywords: multifluid plasma, cfd, boundary conditions