Three-dimensional, unsteady behaviour of high-pressure electric arcs in argon is studied by means of numerical simulations. Attention is paid to argon arcs whose steady structure is fairly well understood. Results are reported for the case of a one centimetre long arc, burning in argon and driven by a total current of 200 A and 300 A. The influence of the boundary conditions for the electrical potential on the macroscopic structure of the arc is studied and it is found that the distribution of the current density near the cathode is one of the critical parameters which can significantly modify both the distribution of mean quantities and the stability of the arc. All mean quantities found from three-dimensional calculations are compared with two-dimensional axi-symmetric fields obtained by a previously used code for arc simulations. The results indicate good agreement between the results from three-dimensional calculations, two-dimensional axi-symmetric simulations and results from physical experiments documented in the literature.

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M : Un mod&le a 6t6 cEvelopp6 pour la prediction d'arcs Bectriques h forte intensit6 et h pression atmosph6rique. Le code M6lodie (diff6rences finies orthogonales) nous a permis de rksoudre le syst&me coup16 d'6quations thermodynamiques et 6lectromagn6tiques incluant effet JOULE et forces de LORENTZ. Dans la colonne cl'arc laminaire, les 6quations sont Ccrites en hypoth2se d'6quilibre thennodynamique local @.TL.), et avec l'approximation de la loi #OHM. Les conditions aux limites h la cathode sont d6terminks B pa& d'un modkle mono-dimensiomel de couche limite cathodique en &&uilibre thermodynamique, coup16 de plus avec le calcul du transfert thermique dans l'6lectrode solide. Les calculs men& dans le cas d'arcs libm ou d'arcs tranf6rCs dans l'argon, avec une cathode wnique en tungsene, ont montr6 un bon accord avec les mesures.: An axisymetric model has been developed for prediction of high intensity electric arcs under atmospheric pressure. A set of thennodynamic and electromagnetic equations, including interaction terms (JOULE effect, LORENTZ forces) is solved using the orthogonal finite difference numerical code M6lodie. Conservation equations in the laminar arc column (mass, momentum, energy and current) are written according to the local thermodynamic equilibrium (L.T.E.) assumption and the OHM law approximation. The proper boundary condition at the cathode is derived from a onedimensional description of non-equilibrium electrode boundary layer, coupled with full computation of heat transfer in solid region (conic cathode in tungsten). Numerical calculations performed for free burning and t r a n s f d argon arcs show a good agreement with experimental data. NOMENCLATURE a subscript of the different specie of the T plasma temperature (K) ..

This paper is devoted to the study of unsteady electric arcs and the effects of electrodes on their dynamics. One of the objectives is to simulate and understand the three-dimensional behaviour of arcs in complex geometries, which create important fluctuations of the column and reattachments on the electrodes. The usual methods to solve the problem of arc–electrodes coupling are not suitable to simulate three-dimensional unsteady arcs. We propose a numerical development to simulate both steady-state and unsteady arcs without additional assumptions. The method is based on the incorporation of electrodes into the computational domain. It is validated with measurements from the literature, in the case of a point–plane steady-state argon arc. The model is used to study the lightning certification test device, which simulates in laboratory the effects of lightning arcs on fuselage panels. The results bring to light, in agreement with the observations in laboratory, the fundamental role of the electrodes on the three-dimensional behaviour of the arc column. The model is also used to simulate the development of the free jet of a plasma on an aluminium planar anode. The objective is to characterize the interaction region and the thermal constraint of the arc.

For a Iran.sJbrred arc with ~1 /7~11 (ltlodc working at tlD~tosl~]l¢'ri (' pr(,ssltrc