Large-eddy simulation and Reynolds-averaged Navier-Stokes modeling of a reacting Rayleigh-Taylor mixing layer in a convergent geometry*

Tenth-order compact difference code Miranda is used to perform large-eddy simulation (LES) of a hydrogen gas/plastic ablator mixing layer in a convergent geometry. Once the mixing layer has achieved self-similar growth, it is heated to 1 keV, and the second-order arbitrary Lagrangian/Eulerian (ALE) code Ares is used to simulate mixing layer evolution as it undergoes thermonuclear (TN) burn. Both premixed and non-premixed variants are considered at Atwood numbers 0.05 and 0.50. The impact of turbulent mixing on mean TN reaction rate is examined, and a four-equation k-L-a-V Reynolds-averaged Navier Stokes (RANS) model is presented. The k-L-a-V model, which represents an extension of the k-L-a model [Morgan and Wickett, Phys. Rev. E 91, 043002 (2015)] by the addition of a transport equation for the scalar mass fraction variance, is then applied in one-dimensional simulations of the reacting mixing layer under consideration. Excellent agreement is obtained between LES and RANS in total TN neutron production when fluctuations in reaction cross-section can be neglected.