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Simulation numérique des écoulements unidimensionnels instationnaires avec autovaporisation

Abstract : The study of the behaviour of safety valves in accident conditions requires to focus on the modelling and the computation of flashing flows. These two-phase flows can occur in any industrial plant, where pressurized liquids are used. During the opening of a safety valve, the dynamics of the disk insert is very dependent on the variations in the pressure field under it. Thus it makes the computation of fast transient flows compulsory. Two research axes were retained : 1°) the physical modelling of flashing phenomenon. 2°) the numerical computation of these models in case of fast transient flows. On a physical point of view, two models for flashing have been studied ; the Homogeneous Relaxation Model (HRM), and the model developed by Jones et al.. They both assume that the pressures and the velocities in each phase are equal, and that the vapour is saturated. The results of these two models have been compared, when focusing on stationnary flows, with the experimental data measured on the loop Super Moby-Dick of the Commissariat a l'Energie Atomique (CEA) in Grenoble (France). Focusing on numerical computation, it may be noticed that the systems of equations obtained with these models are strictly hyperbolic, but they are non conservative in case of one-dimensional flows, because of the occurrence of time and space derivatives of the cross section. Thus the use of Finite Volume numerical schemes to solve them is well adapted. The main difficulties are due to the presence of stiff source terms, and to the use of complex equations of state for real fluid. Three numerical schemes have been studied, VFROE scheme with non conservative variables, Rusanov scheme, and a modified version of Roe scheme. A special attention is given to the computation of boundary conditions. Eventually a comparison of the three schemes has been done, based on the computation of single-phase (gas and liquid) and two-phase transient and steady flows. It shows that VFROE-ncv scheme is the most accurate, and that Rusanov scheme is the most robust. Thus a stategy is proposed combining these two schemes.
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Submitted on : Monday, July 21, 2014 - 3:07:17 PM
Last modification on : Tuesday, October 19, 2021 - 4:08:18 PM
Long-term archiving on: : Monday, November 24, 2014 - 9:15:39 PM

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  • HAL Id : tel-01026372, version 1

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Eric Faucher. Simulation numérique des écoulements unidimensionnels instationnaires avec autovaporisation. Mécanique des fluides [physics.class-ph]. Université Paris XII Val de Marne, 2000. Français. ⟨tel-01026372⟩

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