Thermorelaxing multicomponent flows investigated with a Baer-Nunziato-type model

In inertial confinement fusion (ICF) implosions, mixing the ablator into the fuel and the hot spot is one of the most adverse factors that lead to ignition degradation. Recent experiments in the Marble campaign at the Omega laser facility and the National Ignition Facility demonstrate the significance of the temperature separation in heterogeneous mixing flows [Haines et al., Nat. Commun. 11, 544 (2020)]. In the present work we provide an approach to deal with thermally disequilibrium multicomponent flows with the ultimate aim to investigate the temperature separation impact on mixing and fusion burn. The present work is twofold: (a) We derive a model governing the multicomponent flows in thermal disequilibrium with transport terms and (b) we use the derived model to study the Rayleigh-Taylor (RT) instability in thermally relaxing multicomponent systems. The model is reduced from the full disequilibrium multiphase Baer-Nunziato model in the limit of small Knudsen number Kn << 1. Velocity disequilibrium is closed with the diffusion laws and only one mass-weighted velocity is retained formally. Thus, the complex wave structure of the original Baer-Nunziato model is simplified to a large extent and the obtained model is much more computationally affordable. Moreover, the capability to deal with finite-temperature relaxation is kept. Efficient numerical methods for solving the proposed model are also presented. Equipped with the proposed model and numerical methods, we further investigate the impact of thermal relaxation on the RT instability development at the ICF deceleration stage. On the basis of numerical simulations, we have found that for the RT instability at an interface between the high-density low-temperature component and the low-density high-temperature component, the thermal relaxation significantly suppresses the development of the instability.