Direct numerical simulation of turbulent premixed jet flames: Influence of inflow boundary conditions

Abstract

Direct Numerical Simulations (DNS)s of a low Karlovitz number turbulent premixed round jet flame are performed to determine the impact of the turbulence inflow conditions on the flame characteristics. This is accomplished by providing the first flame with a fully developed turbulent inflow via simulation of the upstream pipe and the coflow region, while the inflow boundary condition in the second flame is generated with a digital filter-based method without including the upstream region. The two databases are then thoroughly compared to reveal any differences resulting from the different inflow boundary conditions. The turbulence kinetic energy is observed to drop shortly downstream of the synthetic inflow, which results in a higher jet momentum and a longer flame compared to the flame with the fully developed turbulent inflow. The distributions of the flame front orientation in the near field are observed to differ between the two flames but differences decrease quickly downstream as distributions tend towards isotropy. The flame structure is largely affected by tangential straining close to the inflow while further downstream, the flame structure is similar to that in an unstrained laminar flame. While the difference between the inflow boundaries had a significant effect on global parameters such as flame length, the influence of the inflow conditions on local statistics related to turbulence-flame interaction appear to be limited to the near inflow region.