Vortex reconnection cascade and turbulence avalanche
Vortex reconnection cascade and turbulence avalanche
Vortex reconnection is a fundamental topology transforming event. Such a topological transformation is considered to play a significant role in flow turbulence such as energy transfer, fine-scale mixing, and noise generation. Vortex reconnection was also found to play an essential role in the transition and friction drag production in the wall-bounded flows. In addition to their physical relevance, reconnection also represents a stand-alone mathematical problem related to the presence of finite time singularity in the Euler equation. With direct numerical simulation up to Re=40000, we report here, for the first time, the evidence of vortex reconnection cascade scenario, where the remaining threads continue to undergo successive reconnections. This observation clearly demonstrates and confirms our long-standing claim that vortex reconnection is an important physical mechanism of turbulent energy cascade, particularly at high Reynolds numbers.
Reconnection plays a significant role in several physical phenomena, such as energy cascade, fine-scale mixing, and noise generation. Similar to reconnection in quantum fluids, we observe that the separation distance for reconnection of slender vortices in classical fluids also scales closely as the square root of the time for both before and after reconnection. The prefactors in the square root law, which are typically larger for post- than the pre-reconnection, show a strong dependence on the initial configuration as well as the Reynolds number. The agreement of our results on classical viscous reconnection with previous numerous works on quantum reconnection suggests that there is a universal route for vortex reconnection.