The lightning swept stroke along an aircraft in flight. Part I: thermodynamic and electric properties of lightning arc channels

During a lightning strike to an aircraft in flight, the lightning channel b ecomes deformed in the airflow and displaced along the aircraft, a so-calle d swept stroke. The deformation and the displacement are caused by the inte raction between the aerodynamic flow and the plasma properties of the chann el together with the properties of the surface. The main part of the lightn ing current is a continuous current with a magnitude of hundreds of amperes and a duration of hundreds of milliseconds. The objective of this article is to analyse the properties of the Lightning channel during this continuou s current phase in order to parametrize them: this parametrization is used in a companion paper (Larsson et al J. Phys. D: Appl. Phys. 33 1876-83) for complete swept-stroke simulations. A model of the thermodynamic evolution of a lightning channel during its continuous current phase is developed and numerically solved, in this model, the channel is assumed to have axial sy mmetry. A quantitative analysis of the influence of failing axial symmetry is also included. The main conclusions are that the steady-state conditions are rapidly reached and that the channel can be considered to he a free-bu rning are subjected to increased thermal losses due to transverse aerodynam ic flow.