Abstract
This work is concerned with the development of a novel, accurate equation of state for describing partially ionized air plasma in local thermodynamic equilibrium. One key application for this new equation of state is the simulation of lightning strike on aircraft. Due to the complexities of species ionization and interaction, although phenomenological curve fitting of thermodynamic properties is possible, these curves are intractable for practical numerical simulation. The large difference in size of the parameters (many orders of magnitude) and complexity of the equations means they are not straightforward to invert for conversion between thermodynamic variables. The approach of this paper is to take an accurate 19-species phenomenological model and use this to generate a tabulated dataset. Coupled with a suitable interpolation procedure, this offers an accurate and computationally efficient technique for simulating partially ionized air plasma. The equation of state is implemented within a multiphysics methodology which can solve for two-way coupling between a plasma arc and an elastoplastic material substrate. The implementation is validated against experimental results, both for a single material plasma and an arc coupled to a substrate. It is demonstrated that accurate, oscillation-free thermodynamic profiles can be obtained, with good results even close to material surfaces.
Highlights
Numerical simulation of air plasma interacting with solid substrates provides insight into the physical mechanisms which lead to structural damage due to lightning strike, which is a key safety concern for aircraft[1]
To accurately understand the physical effects at this attachment, an accurate description of the ionisation processes within the plasma arc is essential. This requires an equation of state (EoS) which can account for the complex thermodynamic and electromagnetic effects arising from partially ionised material
Radial profiles with the oscillatory component V current are shown in Figure 4 for values are compared to the publicly available data of the equation of state developed by Villa, denoted as EOS115,36
Summary
Numerical simulation of air plasma interacting with solid substrates provides insight into the physical mechanisms which lead to structural damage due to lightning strike, which is a key safety concern for aircraft[1]. To accurately understand the physical effects at this attachment, an accurate description of the ionisation processes within the plasma arc is essential This requires an equation of state (EoS) which can account for the complex thermodynamic and electromagnetic effects arising from partially ionised material. The multiple atomic species comprising an air plasma are each governed by different characteristic ionisation energies, governing their initial emergence and further ionisation This leads to a non-linear relationship between intensive thermodynamic variables within the EoS for an air plasma. Computation of these quantities, which on a continuum scale model of a plasma are local physical properties, and are independent of system size, must still take into account transport properties arising from molecular interactions between the different species present
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