Secondary circulation within a mixing box and its effect on turbulence
- PDF / 1,768,132 Bytes
- 13 Pages / 595.276 x 790.866 pts Page_size
- 25 Downloads / 167 Views
RESEARCH ARTICLE
Secondary circulation within a mixing box and its effect on turbulence Hadis Matinpour1 · Joseph Atkinson1 · Sean Bennett2 Received: 27 April 2020 / Revised: 18 September 2020 / Accepted: 21 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract An experimental study was conducted to examine the formation of secondary circulation in a grid-mixing box and to determine its effect on turbulence. This apparatus has been used extensively to study turbulence and mixing in a variety of geophysical contexts, and it is commonly assumed that turbulence is nearly isotropic and horizontally homogenous and that it is a zero-mean shear flow. Exceptions to these assumptions, however, have been reported, where a secondary flow pattern has been observed consisting of two roughly symmetric large-scale circulations with upward flow in the center of the box and downward return flow along the sides. These secondary flows appear to be associated with different grid oscillation conditions and box and grid geometries, and criteria have been proposed to describe conditions when secondary flow may be expected. Experiments were conducted for three different combinations of the grid oscillation stroke and frequency, while maintaining a near constant grid Reynolds number, to examine the formation and strength of the secondary flow and its effect on the magnitude and distribution of turbulence within the box. Velocity characteristics were obtained by particle image velocimetry (PIV). Results show that (1) secondary circulations were present for all combinations of the grid oscillation conditions; (2) as stroke length increased, the intensity of the secondary circulation and the contribution of these motions to total kinetic energy increased; and (3) the presence of secondary circulation results in greater overall mixing and turbulent transport in the region close to the grid. These insights are expected to be relevant to a wide range of mixing box applications.
* Hadis Matinpour [email protected] 1
Department of Civil, Structural and Environmental Engineering, University at Buffalo, Buffalo, USA
Department of Geography, University at Buffalo, Buffalo, USA
2
13
Vol.:(0123456789)
225
Page 2 of 13
Experiments in Fluids
(2020) 61:225
Graphic abstract
1 Introduction and background Turbulence and associated transport characteristics are important for many physical processes on the Earth’s surface. A convenient means of studying turbulence in a laboratory setting is with a mixing box, or oscillating grid tank (OGT), which is a rectangular or cylindrical container with an oscillating grid that produces the mixing motion. In this setup, a planar grid of crossed bars oscillates in the direction normal to the grid (usually vertically) and produces a series of jets and wakes behind the grid bars that spread, interact with each other, and break down into turbulence (Thompson and Turner 1975; Hopfinger and Toly 1976). OGTs have been used in a variety of applications. They were initi
Data Loading...
