Simultaneous temperature and velocity Lagrangian measurements in turbulent thermal convection

TL;DR

This paper presents advanced joint Lagrangian measurements of temperature and velocity in turbulent thermal convection, validating experimental data with numerical simulations and analyzing spectral behaviors to deepen understanding of scalar transport.

Contribution

It introduces an improved neutrally-buoyant instrumented particle for simultaneous temperature and velocity measurements in turbulent convection, enabling detailed Lagrangian heat flux analysis.

Findings

Temperature spectra show an anomalous f^2.5 scaling.

Experimental results agree well with numerical simulations.

Extended autonomy of the particle improves statistical convergence.

Abstract

We report joint Lagrangian velocity and temperature measurements in turbulent thermal convection. Measurements are performed using an improved version (extended autonomy) of the neutrally-buoyant instrumented particle that was used by to performed experiments in a parallelepipedic Rayleigh-Benard cell. The temperature signal is obtained from a RFtransmitter. Simultaneously, we determine particle's position and velocity with one camera, which grants access to the Lagrangian heat flux. Due to the extended autonomy of the present particle, we obtain well converged temperature and velocity statistics, as well as pseudo-eulerian maps of velocity and heat flux. Present experimental results have also been compared with the results obtained by a corresponding campaign of Direct Numerical Simulations and Lagrangian Tracking of massless tracers. The comparison between experimental and numerical results show the accuracy and reliability of our experimental measurements. Finally, the analysis of lagrangian velocity and temperature frequency spectra is shown and discussed. In particular, we observe that temperature spectra exhibit an anomalous f^2.5 frequency scaling, likely representing the ubiquitous passive and active scalar behavior of temperature