Combustion instability is one of the main disadvantages of power generation systems. Indirect noise or acceleration of entropy waves are sound sources that cause the combustion chamber unstable. This subject, however, has been less investigated due to the complex nature of entropy waves. A deep understanding of the physics of entropy waves is crucially important in order to reduce noise and instability. This study considers entropy generation in premixed flame conditions. In this situation, the hydrodynamic and thermal effects on the entropy wave performance in a combustion chamber are studied. To model turbulent flow, the large eddy simulation has been used. The effects of adding hydrogen to the input fuel mixture on entropy wave generation and deterioration in thermal convective and adiabatic combustion have been investigated. Comparing the acoustic noise produced by entropy waves with the studied cases shows the thermo-hydrodynamic effects on the entropy wave in the low-order models of combustion instability prediction, which has been limitedly noticed so far. Although the combustion efficiency is improved by increasing the percentage of hydrogen in the fuel, significant instabilities may occur.
