Direct Numerical Simulation of Autoignition in a Jet in a Cross-Flow Configuration: ALCF-2 Early Science Program Technical Report

Abstract

Autoignition in turbulent flows is a challenging fundamental problem due to the intricate coupling of different physical and chemical processes extending over multiple flow and chemistry scales. At the same time, the improved understanding and ability to predict autoignition in flows characterized by considerable fluctuations of velocity, composition, and temperature is essential for the development of novel low-emission concepts for power generation. The aim of this project is to study the fundamental aspects of autoignition in a fuel-air mixing device directly applicable to mixing ducts in gas turbines. The NEK5000-based code for low Mach number reactive flows is used to perform very large scale direct numerical simulations of autoignition of a diluted hydrogen jet ejected in a cross-flowing stream of hot turbulent air in a laboratory-scale configuration. We report on our experience running NEK5000 on the new BGQ system at ALCF mira during the early science period (ESP). First of all, the most efficient problem size per MPI-rank is obtained through core-level efficiency metric measured from the target simulation. Furthermore, the most efficient number of ranks is found through strong scaling experiments. Finally, low-level insight into the observed parallel efficiency is enabled through IBM's HPC Toolkit libraries.

Combustion Mode and Mixing Characteristics of a Reacting Jet in Crossflow

“…Different from the previous simulations conducted by the same code, the flame structure of nonpremixed fuel jet into vitiated crossflow was uniformly stabilized near the jet exit around its entire circumference. Abdilghanie et al reported a 3D DNS of a nitrogen-diluted hydrogen jet injecting into a crossflowing turbulent stream of preheated air and observed that ignition occurred initially at isolated spots downstream from the jet, and later on a burning flame formed near the jet nozzle . Such a reacting JICF configuration is highly interesting, as a large number of factors like the level of dilution would affect the transient behaviors of ignition and reactions.…”

“…In a series of DNS studies, − ,− the Navier–Stokes equations were solved in their compressible formulation. Since in most cases, a reacting JICF takes place at low Mach numbers, Ma ≪ 1, a large speedup can be obtained using a low-Mach number solver compared to a fully compressible one .…”