On the origin of intrinsic randomness of Rayleigh-Benard turbulence

TL;DR

This paper demonstrates through high-precision simulations that Rayleigh-Benard turbulence can originate intrinsically from thermal fluctuations without external disturbances, linking microscopic uncertainty to macroscopic randomness.

Contribution

It introduces a novel use of clean numerical simulation (CNS) to verify the intrinsic origin of turbulence from thermal fluctuations, improving accuracy over traditional methods.

Findings

Turbulence can self-excite from thermal fluctuations without external disturbances.

System nonlinearity acts as a channel for microscopic uncertainty to influence large scales.

CNS provides a more reliable approach than DNS for turbulent flow simulations.

Abstract

It is of broad interest to understand how the evolution of non-equilibrium systems can be triggered and the role played by external perturbations. A famous example is the origin of randomness in the laminar-turbulence transition, which is raised in the pipe flow experiment by Reynolds as a century old unresolved problem. Although there exist different hypotheses, it is widely believed that the randomness is "intrinsic", which, however, remains as an open question to be verified. Simulating the modeled Rayleigh-Benard convection system by means of the so-called clean numerical simulation (CNS) with negligible numerical noises that are smaller even than thermal fluctuation, we verify that turbulence can be self-excited from the inherent thermal fluctuation, without any external disturbances, i.e. out of nothing. This reveals a relationship between microscopic physical uncertainty and macroscopic randomness. It is found that in physics the system nonlinearity functions as a channel for randomness information, and energy as well, to transport microscopic uncertainty toward large scales. Such scenario can generally be helpful to understand the various relevant phenomena. In methodology, compared with direct numerical simulation (DNS), CNS opens a new direction to investigate turbulent flows with largely improved accuracy and reliability.