Boundary layer structure near roughness in turbulent thermal convection EuHIT Funded Project

### Team

Olivier Liot
Ecole Normale Superieure de Lyon, Lyon, France
Eléonore Rusaouën
Institut Néel, Grenoble, France
Julien Salort
Ecole Normale Superieure de Lyon, Lyon, France

### Overview

Research Infrastructure
Barrel of Ilmenau, Germany
Facilities used
Barrel of Ilmenau (BOI)
In this proposal we would like to measure the detailed structure of the boundary layer near roughness in turbulent thermal convection. This is a greatly interesting problem both from practical ad fundamental point of view. Has been recently measured that roughness increase the heat flux exchange up to 70[1,2]. First measurements seem to indicate an increase of plumes efficiency near the roughness but a general model describing the fundamental mechanism is not available. In Lyon we have realized local measurements in a water cell up to $$10^{10}$$ but the boundary layers thickness can be about then 300 microns and do not allows a complete analysis, particularly in the case velocity. In the BOI configuration with height 2.5m, the boundary layer thickness is about 6 mm, so 10 times larger than in our water cell, at nearly the same Rayleigh number. The two combined experiences (Ilmenau and Lyon) of fine flow measurements inside the boundary layers, will allow us to extent our recent results on the boundary layer structure near roughness and a to lead general improvement in the knowledge of the physical phenomenon. We plan to realize PIV measurements of the velocity field under supervision of R. du Puits, in the framework of EuHIT JRA 21. Moreover we plan to use a technique not exploitable in water but useful in air and available in Ilmenau: an Infra-Red camera that directly measures the heat flux above and between the roughness.