A Laboratory-Scale Experiment and a Numerical Simulation of Unusual Spiral Plumes in a High-Prandtl-number Fluid

TL;DR

This study combines laboratory experiments and numerical simulations to investigate the formation of unusual spiral plumes in a high-Prandtl-number fluid, revealing mechanisms relevant to mantle convection and geophysical phenomena.

Contribution

It introduces a combined experimental and numerical approach to study spiral plume formation in high-Prandtl-number fluids, linking laboratory results to mantle convection models.

Findings

Spiral plumes resemble vertical Archimedes spirals.

Numerical simulations confirm physical mechanisms behind spiral formation.

Results suggest relevance to mantle tomography interpretations.

Abstract

We experimentally and numerically investigated the generation of plumes from a local heat source (LHS) and studied the interaction of these plumes with cellular convective motion (CCM) in a rectangular cavity filled with silicon oil at a Prandtl number (Pr) of approximately two thousand. The LHS is generated using a 0.2-W green laser beam. A roll-type CCM is generated by vertically heating one side of the cavity. The CCM may lead to the formation of an unusual spiral convective plume that resembles a vertical Archimedes spiral. A similar plume is obtained in a direct numerical simulation. We discuss the physical mechanism for the formation of a spiral plume and the application of the results to mantle convection problems. We also estimate the Reynolds (Re) and Rayleigh (Ra) numbers and apply self-similarity theory to convection in the Earth's mantle. Spiral plumes can be used to interpret mantle tomography results over the last decade.