Pattern Formation in Thermal Convective Systems: Spatio-temporal Thermal Statistics, Emergent Flux, and Local Equilibrium

TL;DR

This paper investigates pattern formation in thermal convective systems through numerical and experimental studies, analyzing surface temperature statistics and emergent flux in hydrothermal waves and Rayleigh-Bénard convection.

Contribution

It introduces a comparative analysis of thermal pattern formation in two different convective systems, highlighting universal statistical behaviors despite different mechanisms.

Findings

Surface temperature distributions show phase separation into order and disorder.

Emergent flux patterns are consistent across different convective regimes.

Thermal distributions exhibit macroscopic similarities despite distinct instabilities.

Abstract

We discuss spatio-temporal pattern formation in two separate thermal convective systems. In the first system, hydrothermal waves (HTW) are modeled numerically in an annular channel. A temperature difference is imposed across the channel, which induces a surface tension gradient on the free surface of the fluid, leading to a surface flow towards the cold side. The flow pattern is axially symmetric along the temperature gradient with an internal circulation for a small temperature difference. This axially symmetric flow (ASF) becomes unstable beyond a given temperature difference threshold, and subsequently, symmetry-breaking flow, i.e., rotational oscillating waves or HTW, appears. For the second system, Rayleigh-B\'enard convection (RBC) is experimentally studied in the non-turbulent regime. When a thin film of liquid is heated, the competing forces of viscosity and buoyancy give rise to convective instabilities. This convective instability creates a spatio-temporal non-uniform temperature distribution on the surface of the fluid film. The surface temperature statistics are studied in both these systems as `order' and `disorder' phase separates. Although the mechanisms that give rise to convective instabilities are different in both cases, we find an agreement on the macroscopic nature of the thermal distributions in these emergent structures.