로켓엔진 연소기의 연소안정화를 위한 수동제어기구 설계 기준 구축

Abstract

The objective of the present study is to establish the basic design criteria on passive control devices such as baffle and acoustic-cavity for enhancement of combustion stability in a liquid rocket engine. The first method is to use a baffle of the passive stabilization devices in order to ensure the combustion stability. In this study, we will use a baffled injector instead of typical baffle. Acoustic damping induced by gap of baffled injectors is investigated numerically, which are installed to suppress pressure oscillations in a rocket combustor. The previous work reported that the baffled injectors showed larger acoustic damping with the gap between injectors. It is simulated numerically in this study and its mechanism is examined. Damping factors are calculated as a function of gap of the baffled injectors and it is found that the optimum gap is 0.1 mm or so. For understanding of the improved damping induced by the gap, dissipation rate of turbulent kinetic energy and vorticity are calculated as a function of the gap. Both parameters have each maximum value at the specific gap and especially, the dissipation rate has the same profile as that of damping factor. It verifies that the improved damping made by the gap is attributed to the increased acoustic-energy dissipation. The other method is to use an acoustic cavity and Helmholtz type resonator, in particular. The acoustic behavior in combustion chamber with acoustic cavity is numerically investigated by adopting linear acoustic analysis. From the numerical results, tuning frequency and geometric factor of acoustic cavity are found, respectively. Although acoustic stability is ensured from cold condition, gas property will be changed by inflow of gas product in acoustic cavity during a combustion. Inflow of gas product increases gas temperature in an acoustic cavity and brings about change of sound speed. Accordingly, acoustic cavity is redesigned for better tuning.