Non-conforming Schwarz-spectral element method for low Mach number reacting flows

Overlapping-domain methods together with current exascale computing capabilities can provide significant speedup to large-scale direct numerical simulations (DNS). The objective of this work is to examine the accuracy and performance of the non-conforming Schwarz method for the simulation of low Mach number reacting flows using the spectral element solver Nek5000. The overlapping-domain approach already implemented in Nek5000 for incompressible non-reacting scenarios is extended to reacting flows in open domains. First, the spatial and temporal convergence properties of the method were tested using the analytical solution for a 1-D reacting transient model problem developed for this purpose. The results show that the method preserves the exponential convergence in space with respect to polynomial order and exhibits a third-order accuracy in time, when the flame front is located away from the interdomain boundaries.When the flame approaches the interdomain boundaries, a first-order accuracy in time is observed, similar to non-reacting flows in overlapping domains when no sub-iterations are performed. Additionally, a simulation of a propagating turbulent lean premixed H-air flame in a 2-D circular domain was conducted, demonstrating that with adequate resolution in both overlapping domains, the flame transitions smoothly from the inner to the outer domain. Subsequently, a DNS of a 3-D early flame kernel development (EFKD) in decaying homogeneous isotropic turbulence (HIT) was carried out to assess accuracy and performance of the method under turbulent conditions, closely resembling scenarios during the initial phase of internal combustion engines (ICEs). Temperature and species profiles, flame consumption speed, as well as other quantities of interest, were found to be in very good agreement with single-domain results, showing that the method retains its accuracy. Finally, a strong scaling study of the EFKD configuration reveals that the parallel performance and speedup show the expected behavior of the overlapping-domain method for low Mach number reacting flows.