Penetration process and instabilities arisen on a liquid jet impinged to a liquid flowing in a channel

We conduct a series of experiments with a special interest on a penetration process and instabilities arisen on a liquid jet impinged to a liquid of the same kind flowing in a channel. The impinged jet penetrates into the flowing bath accompanying with entrainment of the ambient immiscible gas, which results in the impinged jet wrapped by the entrained gas as a ``sheath.'' This sheath formation enables the impinged jet to survive in the fluid in the channel without coalescing until the entrained-air sheath breaks down. Occasionally a ``cap'' of the entrained air is formed at the tip of the penetrated jet, and the jet elongates like a long balloon. Dynamic behaviors of the penetrated jet and the departure of the bubble of warring gas at the tip of the collapsing jet observed by use of a high-speed camera are discussed.