Lagrangian dispersion and heat transport in convective turbulence

TL;DR

This paper investigates Lagrangian heat transport in turbulent Rayleigh-Benard convection through DNS, revealing anisotropic Richardson dispersion, plume-related acceleration patterns, and height-dependent mixing zones.

Contribution

It provides new insights into Lagrangian dispersion and heat transfer mechanisms in anisotropic turbulent convection, highlighting the role of plumes and acceleration statistics.

Findings

Lateral pair distances follow Richardson law with a smaller constant.

Vertical accelerations are less frequent and not linked to plumes.

Identified a zone dominated by thermal plume mixing.

Abstract

Lagrangian studies of the local temperature mixing and heat transport in turbulent Rayleigh-Benard convection are presented, based on three-dimensional direct numerical simulations. Contrary to vertical pair distances, the temporal growth of lateral pair distances agrees with the Richardson law, but yields a smaller Richardson constant due to correlated pair motion in plumes. Our results thus imply that Richardson dispersion is also found in anisotropic turbulence. We find that extremely large vertical accelerations appear less frequently than lateral ones and are not connected with rising or falling thermal plumes. The height-dependent joint Lagrangian statistics of vertical acceleration and local heat transfer allows us to identify a zone which is dominated by thermal plume mixing.