On velocity and temperature fluctuations generated by a turbulent grid and driven by buoyancy in open vertical channel

¹ Faculty of Physics, Theoretical and Applied Laboratory of Fluid Mechanics, University of Science and Technology Houari Boumedienne, BP No. 32 El Alia 16111 Algiers, Algeria
² Institute Mining-Telecommunication, 37-39 rue Dareau, Paris, France

^a Corresponding author: mmahamdia2005@yahoo.fr

Received: 8 December 2015
Accepted: 20 September 2016

Abstract

This paper presents an experimental analysis of the statistical properties of velocity and temperature fluctuations generated downstream of two plan grids placed at the inlet of a large vertical open channel. A uniformly heated grid with a mesh spacing of M_θ = 10 cm is placed underneath a second unheated turbulence-generating grid with a mesh spacing of M = 30 cm. Buoyancy is the only driving force, and air is used as the working fluid and is heated from below Themeasurements of thegenerated turbulence are performed with the hot and cold-wire anemometry. It is shown experimentally that the turbulence behind the grid is inhomogeneous in its mean velocity and in its turbulence quantities. Even far downstream of the grid, the inhomogeneity of the mean velocity and the turbulence fluctuations persists. Regarding the longitudinal evolution of the mean turbulence, it is found that evolutions of the velocity and temperature variances are in contrast with the evolutions which are generally observed in forced convection turbulence grids. However, in the first part of the flow, x/M ≤ 13.33, the mean temperature variance decreases and evolves in agreement with the variance generally observed in homogeneous and isotropic grid turbulence flow.