Large Eddy simulation of the effects of radiative heat loss on combustion instability prediction

Abstract

This study examined the influence of various chemical reaction mechanisms and heat loss conditions on the prediction of longitudinal combustion instability in the Continuous Variable Resonance Combustor (CVRC). To assess the impact of chemical reaction mechanisms on the prediction of longitudinal combustion instability modes, both global and skeletal mechanisms were used, while adiabatic wall conditions were employed to eliminate the effects of heat loss. To evaluate the effect of heat loss conditions on the prediction of combustion instability modes, investigations were conducted under three different conditions: adiabatic wall, isothermal wall, and considering thermal radiation using the simple P1 model and the gray gas model. Radiative heat loss was calculated using a radiative convection boundary condition, while heat loss through wall convection was ignored. The dominant frequency, temperature field, pressure field, and combustion instability development mechanism were analyzed based on the numerical results and compared with experimental data and previous numerical studies. The use of a skeletal mechanism and the consideration of heat loss were found to reduce the difference in combustion instability mode frequency compared to experimental data. The results showed that maintaining an isothermal wall temperature effectively decreased the difference in the dominant frequency compared to experiments, but had limitations in reducing pressure fluctuation amplitudes. Additionally, incorporating thermal radiation did not significantly decrease the difference in the first mode frequency compared to experimental data, although it kept the range of pressure fluctuations within a reasonable level. Therefore, this study underscores the importance of accurate temperature prediction for evaluating thermal-acoustic instability frequencies and highlights the necessity of using a chemical reaction mechanism that accurately predicts the adiabatic flame temperature and heat loss conditions.