Characterization of high-current pulsed arcs ranging from 100--250 kA peak

In this paper, we present the laboratory study on three experimental setups that produce a free arc channel subjected to the transient phase of a lightning current waveform. This work extends the high-current pulsed arc characterization performed in previous studies for peak levels up to 100 kA. Eleven high-current waveforms with peak value ranging from 100--250 kA with different growth rates and action integrals are studied, allowing the comparison of different test benches. These waveforms correspond to standard lightning ones used in aircraft certification processes. Hydrodynamic properties such as arc channel evolution and shock-wave propagation are determined by high-speed video imaging and the background-oriented Schlieren method. The arc diameter reaches around 90mm at 50 $\mu$s for a current of 250 kA peak. Space- and time-resolved measurements of temperature, electron density and pressure are assessed by optical emission spectroscopy associated with the radiative transfer equation. It is solved across the arc column and takes into account the assumption of non-optically thin plasma at local thermodynamic equilibrium. For a 250 kA waveform, temperatures up to 43000K are found, with pressures in the order of 50 bar. The influence of current waveform parameters on the arc properties are analyzed and discussed

Modeling and simulation of sparking in fastening assemblies.

This paper deals with modeling and simulation of sparking occurrence in fastening assemblies. The principle consists to calculate in three dimensions the distributions of current density and temperature in the structure over time, and to derive some physical criteria to estimate the possibility of sparking occurrence. Simulations are performed with a Finite Volume Method in time domain and an unstructured mesh. Low frequency assumption is considered for the calculations of electromagnetic quantities (quasi static assumption). The contact resistances between each elements of the structure are also considered, assuming a uniform distribution of the resistance on the interfaces. The two main mechanisms involved in the non-linear behavior of the fastener during high current components are also modeled. First, dielectric breakdowns of sealant layers are simulated with their dielectric strength. Two different situations are simulated. In the case of a direct attachment of the lighting arc on the fastener, the current enters the assembly through the bolt. In the case of conduction, the current (fraction of D component) passes from the skin to the rib through the bolt. The results of simulations bring to light the role of the contact resistances between the bolt and other elements (rib, skin, nut...) on the occurrence of sparking. In some case, computations indicate some important reinforcements of the current density of more than 10kA/mm², resulting to a strong local heating of the bolt and a possible sparking occurrence

Numerical investigation of the surface effects on the dwell time during the sweeping of lightning arcs

International audienceDuring a lightning strike in flight, the arc sweeps back along the aircraft surface by jump under the effects of the aerodynamic flow. This mechanism is called swept stroke. The dwell times at each attachment point vary according to the nature of the surface; the local geometry and air flow; and the current waveform which could cause reattachment if a current peak occurs. This paper is focused on the effects of the surface on the dwell time value. The parameters studied are the thickness of the boundary layer, and the presence of insulating coatings on the surface. 3D Numerical simulations of DC arcs along planar surfaces in the presence of a flow are carried out based on the Magneto Hydrodynamic (MHD) approach. The dynamics and the arcs instabilities are investigated with a special attention to the expansion radius, the tortuosity, and the internal voltage gradient. The effects of the boundary layer thickness and the presence of insulating layers on the dwell-time are discussed and the criteria for reattachment are examined. Finally, an example of dwell-time estimation is considered and the effects of electric and thermal constraints are discussed

Simulation of the Lightning Arc Root Interaction with Anisotropic Materials

International audienceThe interaction between lightning arcs and composite materials is a challenging issue for maintenance and safety considerations in the aerospace industry [1]. Composite materials exhibit a much lower conductivity than metallic materials, as well as an important anisotropy due to the orientation of the fibres and the insulating nature of the matrix. In this study, the impact of the anisotropy of composite materials on the lightning arc root dynamics during the pulsed arc phase has been focused. A finite-volume compressible MHD code including Joule heating, Laplace forces and radiative fluxes has been used in a simplified 2D configuration with a single layer composite material. The different current distributions in the arc root are examined up to 30 µs for different ratios between longitudinal and perpendicular conductivities

Study of a high current arc used for direct lightning effect characterization

International audienceComposite materials are used in aeronautics for their mechanical properties and their lightness. Unfortunately, their conductivity is not isotropic and is lower than Aluminum, the material previously used. When a lightning event occurs, if the material resistance is too high, the current flowing in the structure may induce damage. To prevent this, new aeronautic materials are tested according to the following test procedure: a 100 kA impulse current flows in the material through a 10 cm arc. As our team develops codes on this problematic [1] to model and simulate the effect of such high current on new materials, we built a test bench producing a 10 cm arc of 100 kA with a biexponential current curve as defined by the aeronautic standard. The measurements obtained with this system will provide necessary data to validate our MHD simulation code

Study of the interaction of a free burning arc and an aluminium panel

International audienceWe developed at ONERA a 400 A dc current generator at a voltage of 1600 V to analyse the freeburning arc interaction with a material for lightning applications. This voltage allows the generation of a long arc with a channel length ranging from 10 to more than 40 cm in some cases. With this experiment we studied the interaction of a generated arc root and a material under test; aluminium in this study. In particular, we focused on a regime exhibiting a stable plasma jet ejected from the panel. The aim is to gather experimental data to perform a comparison with previously published numerical results showing a similar behaviour [1]. In a first part, we present the experimental set-up namely the generator, the ignition method of the arc and the experimental set-up. In a second part we describe the results obtained on the plasma using fast imaging (100 kHz) and fast emission spectroscopy (10 kHz). In a third part we use fitting methods on the emission spectra and deduced electronic temperature. Finally, the presence of some magnesium metallic lines due to thevaporisation of the panel is discussed

Experimental characterization fo the interaction between a high current arc and aeronautical materials

International audienceIn this paper, we present the work realized on an experimental setup which simulates in laboratory the transient phase of a lightning arc applied to aluminum samples with different thicknesses and surface coatings. A high current pulsed arc is utilized in this study, which has a peak value of 100 kA and a peak time to around 12 μs. This device is instrumented with high speed video cameras to assess the geometric characteristics of the arc attachment on the material.The shock wave generated by the arc expansion is analyzed near to the surface material, using theBackground-Oriented Schlieren method. The position and velocity of the wave front and the arc root radius are determined up to 70 μs, when the lightning arc is applied to aluminum samples with different paint thickness. Finally, we perform comparisons with previous results of the hydrodynamic properties of a free arc channel subjected to the same level of current, but without the material’s interaction