Influence of Chemical Modeling on URANS Simulations of Longitudinal Thermoacoustic Instability

This study investigates the impact of ignition delay modeling on the prediction of thermoacoustic instabilities using a two-dimensional axisymmetric Unsteady Reynolds-Averaged Navier-Stokes approach. The Continuously Variable Resonance Combustor, a well-documented test case known for exhibiting longitudinal combustion instability, is used as reference for this analysis. After assessing the primary role of ignition delay in the numerical prediction of thermoacoustic instabilities, a set of simplified one-step oxymethane chemical mechanisms, each calibrated to represent different ignition delays, is examined. The study focuses on identifying how variations in ignition delay influence key observables of combustion instability, specifically the amplitude and frequency of pressure oscillations in the resulting limit cycle. The main objective is to show how physics-based assumptions in chemical modeling can improve the accuracy of predictions and lead to better agreement with experimental results.