One Experimental Observation of Steady Standing Wave in Co-flow System*

Dripping and jetting are two common regimes of the co-flow system. However, we usually observe wavy jets on the transition boundary between the dripping regime and the jetting regime. In this paper, we report one experimental observation of the steady standing wave in the co-flow system near the transition boundary. With this observation, we further examine the steady standing wave induced by the downstream boundary condition with respect to both the absolute instability and the convective instability. The downstream cross-sectional change can potentially stabilize the co-flow interface.