Study on Flame Response Characteristics under Transverse Pressure Excitations

Abstract

The main objective of the present study is to experimentally investigate characteristics of combustion dynamics under circumferential acoustic environments induced by an external perturbation device. One of critical combustion dynamic problems among liquid rocket engines and lean premixed gas turbine engines is the occurrence of high-frequency combustion instability coupled to resonant modes of a combustor. It becomes very crucial to examine relations between heat release rate from combustion and pressure fluctuations for the understanding this phenomenon. The common goal of the related research works falls into finding out the response function between heat release rate fluctuations and pressure or velocity fluctuations. One of experimental approaches is to actively apply external pressure perturbations and to measure and analyze response of flame. Therefore, it becomes more realistic to put flame of interest under transverse acoustic environments since acoustic modes of combustion instabilities observed in actual combustion devices are tangential ones. A novel experimental apparatus has been devised for the investigation of relations between flame heat release rate and acoustic pressure fluctuations in terms of a flame response function. External acoustic excitations by a loud speaker are introduced into the combustion chamber in the tangential direction. The induced pressure waves sweep the premixed swirl flame in the lateral direction, which simulates the pressure perturbations in transverse modes. The combustion chamber has a donut-like shape intended for simulating annular acoustic environments of practical gas turbines. Also, the donut-like combustion chamber allows excited pressure waves to travel in the chamber without reflection.