On the collision of laminar jets: fluid chains and fishbones

We present the results of a combined experimental and theoretical investigation of the family of free-surface flows generated by obliquely colliding laminar jets. We present a parameter study of the flow, and describe the rich variety of forms observed. When the jet Reynolds number is sufficiently high, the jet collision generates a thin fluid sheet that evolves under the combined influence of surface tension and fluid inertia. The resulting flow may take the form of a fluid chain: a succession of mutually orthogonal links, each composed of a thin oval film bound by relatively thick fluid rims. The dependence of the form of the fluid chains on the governing parameters is examined experimentally. An accompanying theoretical model describing the form of a fluid sheet bound by stable rims is found to yield good agreement with the observed chain shapes. In another parameter regime, the fluid chain structure becomes unstable, giving rise to a striking new flow structure resembling fluid fishbones. The fishbones are demonstrated to be the result of a Rayleigh-Plateau instability of the sheet's bounding rims being amplified by the centripetal force associated with the flow along the curved rims.