Direct Numerical Simulation Study of an Experimental Lifted H₂/N₂ Flame. Part 1: Validation and Flame Structure

Abstract

Direct numerical simulation (DNS) is used to investigate an experimental lifted turbulent H 2 /N 2 flame in a co-flow of hot products of lean H 2 /air combustion. The DNS code solves the fully compressible Navier–Stokes equations. A fourth-order explicit Runge–Kutta method for time integration and an eighth-order central differencing scheme for spatial discretization are used. A detailed 9 species and 19-step mechanism for hydrogen combustion is employed. The inflow turbulence is considered by adding a random velocity field to the mean flow. The Reynolds number based on the exit diameter and jet velocity is 23 600. In total, more than 285 million grids are used, and the grid spacing is sufficient to resolve all of the turbulence scales and the flame structure. The comparison of the DNS results and the measurements is carried out for various scalars, including the mixture fraction, temperature, and mass fractions of H 2, O 2, H 2 O, and OH. Good agreements are observed for the Favre mean and fluctuating components, which validate the present approach and code. The overall flame structure is also outlined. Two combustion modes are identified in the lifted flame, and the non-premixed combustion dominates.