The formation of large-scale streams in two-dimensional turbulence

Following the suggestion from previous Monte--Carlo experiments (Jim\'enez, J. of Turbul., 2020), that dipoles are as important to the dynamics of decaying two-dimensional turbulence as individual vortex cores, it is found that the kinetic energy of this flow is carried by elongated streams formed by the concatenation of dipoles. Vortices separate into a family of small fast-moving cores, and another family of larger slowly moving ones, which can be described as `frozen' into a slowly evolving `crystal'. The kinematics of both families are very different, and only the former is self-similar. The latter is responsible for most of the kinetic energy of the flow, and its vortices form the dipoles and the streams. A mechanism is proposed for the growth of this slow component, and it is suggested that crystallisation drives the energy cascade towards larger scales