Horizontal velocity field near the hot plate in turbulent natural convection

TL;DR

This study investigates the velocity field near the hot plate in turbulent natural convection using PIV, revealing deviations from classical boundary layer profiles and supporting the existence of natural convection boundary layers on line plumes.

Contribution

It provides experimental validation of the natural convection boundary layer profile and its deviation from classical laminar profiles in turbulent conditions.

Findings

Velocity boundary layer agrees with natural convection theory

Mean velocity deviates from classical profiles depending on plume orientation

Supports the presence of boundary layers on both sides of line plumes

Abstract

We study the velocity field in a horizontal (x-y) plane 1.5 mm above the hot plate in turbulent natural convection using PIV at a Rayleigh number Raw=106 and Prandtl number Pr=5.2. The plane of measurement is inside the velocity boundary layer estimated from the natural convection boundary layer equations[7] as well as inside the velocity boundary layer due to the large scale flow[2, 5].The boundary layer comprises of line plumes with sinking fluid between them. The instantaneous velocity variation from the center of the sinking fluid to the line plumes is found to deviate with the classical Prandtl-Blasius laminar boundary layer profile, which is assumed to be the nature of boundary layer by the GL theory [2, 5]. Our results agree well with the natural convection boundary layer profile. The time averaged mean velocity variation deviates from both natural convection and Blasius type profiles as expected as it depends on the orientation of the line plumes. Our measurement result is a proof to the theory of the presence of a natural convection boundary layer on both sides of a line plume [10].