Experimental study on gravity currents flowing on heated walls

TL;DR

This experimental study investigates how heated walls affect steady gravity currents, analyzing flow dynamics, turbulence, and stratification under different heating conditions through detailed measurements and flux estimations.

Contribution

The paper introduces a comprehensive experimental protocol for characterizing heated gravity currents, including simultaneous multi-parameter measurements and flux estimations under various wall heating scenarios.

Findings

Heated walls create a stratified boundary layer affecting flow statistics.

Wall heating influences shear, buoyancy, and turbulence production.

No clear trend in Richardson numbers with different wall heat fluxes.

Abstract

We present an experimental study on steady gravity currents advancing along a heated wall. The current is generated by a mixture of air and carbon dioxide continuously supplied at the channel inlet. To have a complete point-wise characterization of the flow, simultaneous high-frequency measurements of two velocity components, CO_2 concentration, and temperature are performed. An experimental protocol is presented to reconstruct the local fluid density and to estimate turbulent vertical and horizontal fluxes of CO_2, temperature, and buoyancy. The reliability of both the flow measurements and of the estimate of convective heat flux exchanged at the wall is assessed through integral balances of \textnormal{CO}$_2$ mass, enthalpy, and buoyancy, performed at different distances from the source. Three wall-heating conditions are considered: an adiabatic case, a moderately heated case, and a strongly heated case. In the heated experiments, a convectively unstable boundary layer forms near the wall, capped by a stably stratified region. The influence of this condition on the first- and second-order flow statistics profiles is examined. Although wall heating influences the vertical shear, the Brunt-Vaisala frequency, and both shear and buoyancy production of turbulent kinetic energy within the stably-stratified region characterized by an almost constant vertical gradient of streamwise velocity, neither the gradient Richardson number nor the flux Richardson number exhibits a clear trend in this region with the imposed wall heat flux.