The effects of atomic-level rnixing are systemically investigated in a multifluid interpenetration mix model ,and results are compared with the single-fluid model＇s simulations and experimental data. It is shown that...The effects of atomic-level rnixing are systemically investigated in a multifluid interpenetration mix model ,and results are compared with the single-fluid model＇s simulations and experimental data. It is shown that increasing the model free parameter α, shock Mach number, and the initial density discontinuity makes the mix length and fraction of mixing particle increase, resulting in the lower shock temperatures compared with the results of single-fluid model without mixing. Recent high-compressibility direct-drive spherical implosions on OMEGA are simulated by the interpenetration mix modal. The calculations with atomic mixing between fuel and shell match quite well with the observations. Without considering any mixing, the calculated neutron yields and ion temperatures are overpredicted; while inclusion of the interpenetration mix model with the adjustable parameter α could fit the simulated neutron yields and ion temperatures well with experimental data.展开更多
Diffuse interfaces appear with any Eulerian discontinuity capturing compressible flow solver. When dealing with multifluid and multimaterial computations, interfaces smearing results in serious difficulties to fulfil ...Diffuse interfaces appear with any Eulerian discontinuity capturing compressible flow solver. When dealing with multifluid and multimaterial computations, interfaces smearing results in serious difficulties to fulfil contact conditions, as spurious oscillations appear. To circumvent these difficulties, several approaches have been proposed. One of them relies on multiphase flow modelling of the numerically diffused zone and is based on extended hyperbolic systems with stiff mechanical relaxation (Saurel and Abgrall, 1999 [4], Saurel et al., 2009 [6]). This approach is very robust, accurate and flexible in the sense that many physical effects can be included: surface tension, phase transition, elastic-plastic materials, detonations, granular effects etc. It is also able to deal with dynamic appearance of interfaces. However it suffers from an important drawback when long time evolution is under interest as the interface becomes more and more diffused. The present paper addresses this issue and provides an efficient way to sharpen interfaces. A sharpening flow model is used to correct the solution after each time step. The sharpening process is based on a hyperbolic equation that produces a steady shock in finite time at the interface location. This equation is embedded in a “sharpening multiphase model” redistributing volume fractions, masses, momentum and energy in a consistent way. The method is conservative with respect to the masses, mixture momentum and mixture energy. It results in diffused interfaces sharpened in one or two mesh points. The method is validated on test problems having exact solutions.展开更多
The treatment of moving material interfaces and their vicinity is very important for compressible multifluids. In this paper, we propose one type of ghost fluid method based on Riemann solutions for front tracking met...The treatment of moving material interfaces and their vicinity is very important for compressible multifluids. In this paper, we propose one type of ghost fluid method based on Riemann solutions for front tracking method. The accuracy of the interface boundary condition is discussed for the gas-gas Riemann problem. It is shown that the solution of the ghost fluid method approximates the exact solution to second-order accuracy in the sense of comparing to the exact solution of a Riemann problem at the material interface. Numerical examples suggest that the present scheme is able to handle multifluids problems with large density differences and has the property of reduced conservation error.展开更多
基金Supported by the National Basic Research Program of China under Grant No.2007CB815100the National Natural Science Foundation of China under Grant Nos.10775020 and 10935003
文摘The effects of atomic-level rnixing are systemically investigated in a multifluid interpenetration mix model ,and results are compared with the single-fluid model＇s simulations and experimental data. It is shown that increasing the model free parameter α, shock Mach number, and the initial density discontinuity makes the mix length and fraction of mixing particle increase, resulting in the lower shock temperatures compared with the results of single-fluid model without mixing. Recent high-compressibility direct-drive spherical implosions on OMEGA are simulated by the interpenetration mix modal. The calculations with atomic mixing between fuel and shell match quite well with the observations. Without considering any mixing, the calculated neutron yields and ion temperatures are overpredicted; while inclusion of the interpenetration mix model with the adjustable parameter α could fit the simulated neutron yields and ion temperatures well with experimental data.
文摘Diffuse interfaces appear with any Eulerian discontinuity capturing compressible flow solver. When dealing with multifluid and multimaterial computations, interfaces smearing results in serious difficulties to fulfil contact conditions, as spurious oscillations appear. To circumvent these difficulties, several approaches have been proposed. One of them relies on multiphase flow modelling of the numerically diffused zone and is based on extended hyperbolic systems with stiff mechanical relaxation (Saurel and Abgrall, 1999 [4], Saurel et al., 2009 [6]). This approach is very robust, accurate and flexible in the sense that many physical effects can be included: surface tension, phase transition, elastic-plastic materials, detonations, granular effects etc. It is also able to deal with dynamic appearance of interfaces. However it suffers from an important drawback when long time evolution is under interest as the interface becomes more and more diffused. The present paper addresses this issue and provides an efficient way to sharpen interfaces. A sharpening flow model is used to correct the solution after each time step. The sharpening process is based on a hyperbolic equation that produces a steady shock in finite time at the interface location. This equation is embedded in a “sharpening multiphase model” redistributing volume fractions, masses, momentum and energy in a consistent way. The method is conservative with respect to the masses, mixture momentum and mixture energy. It results in diffused interfaces sharpened in one or two mesh points. The method is validated on test problems having exact solutions.
文摘The treatment of moving material interfaces and their vicinity is very important for compressible multifluids. In this paper, we propose one type of ghost fluid method based on Riemann solutions for front tracking method. The accuracy of the interface boundary condition is discussed for the gas-gas Riemann problem. It is shown that the solution of the ghost fluid method approximates the exact solution to second-order accuracy in the sense of comparing to the exact solution of a Riemann problem at the material interface. Numerical examples suggest that the present scheme is able to handle multifluids problems with large density differences and has the property of reduced conservation error.
