Direct Numerical Simulation of Pulsating Jet Mixing

In lean premixed combustors, the fuel/air ratio oscillation can cause a serious problem since it can produce pressure and heat release fluctuations, and further, combustion instability if it is well phased with them. In order to design a system where such air/fuel ratio fluctuation is well suppressed, it is important to understand the mixing process and its interaction with the flow structures inside a premixer. In this study, the flow-field of a pulsating jet and the mixing of the jet with the co-flow are examined using direct numerical simulation. The effects of the frequency and amplitude of the imposed pulsation on the flow structures and mixing process are investigated in detail. It is found that the modulation amplitude has a favorable effect on mixing, but the dependency on frequency is more complicated.