Digital twin of a large-aspect-ratio Rayleigh-B\'enard experiment: Role of thermal boundary conditions, measurement errors and uncertainties

TL;DR

This study creates a digital twin of a Rayleigh-Bénard convection experiment to identify causes of discrepancies between experiments and simulations, revealing calibration errors and the impact of thermal boundary conditions.

Contribution

It introduces a detailed digital twin of a large-aspect-ratio convection experiment, analyzing the effects of boundary conditions and measurement errors on observed flow structures.

Findings

Discrepancies in flow size are due to thermal boundary conditions and calibration errors.

Re-analysis of experimental data shows a 24% increase in vertical velocity magnitude.

Corrected data resolves previous differences between experiments and simulations.

Abstract

Albeit laboratory experiments and numerical simulations have proven themselves successful in enhancing our understanding of long-living large-scale flow structures in horizontally extended Rayleigh-B\'enard convection, some discrepancies with respect to their size and induced heat transfer remain. This study traces these discrepancies back to their origins. We start by generating a digital twin of one standard experimental set-up. This twin is subsequently simplified in steps to understand the effect of non-ideal thermal boundary conditions, and the experimental measurement procedure is mimicked using numerical data. Although this allows explaining the increased observed size of the flow structures in the experiment relative to past numerical simulations, our data suggests that the vertical velocity magnitude has been underestimated in the experiments. A subsequent re-assessment of the latter's original data reveals an incorrect calibration model. The re-processed data show a relative increase in $u_{z}$ of roughly $24 \%$, resolving the previously observed discrepancies. This digital twin of a laboratory experiment for thermal convection at Rayleigh numbers $\Ra = \left\{ 2, 4, 7 \right\} \times 10^{5}$, a Prandtl number $\Pr = 7.1$, and an aspect ratio $\Gamma = 25$ highlights the role of different thermal boundary conditions as well as a reliable calibration and measurement procedure.