Publication Date:
1983-02-01
Description:
Experiments are described in which a grid is towed horizontally along a large tank filled first with water and then with a stably stratified saline solution. The decay rates of the r.m.s. turbulent velocity components (w′, v′) perpendicular to the mean motion are measured by a ‘Taylor’ diffusion probe and are found to be unaffected by the stable stratification over distances measured from 5 to 47 mesh lengths (M) downstream, and over a range of Froude number U/NM of ∞ and 8.5 to 0.5, U being the velocity and N the buoyancy frequency. The Reynolds number Mw′/v of the turbulence was about 103, where v is the kinematic viscosity. The vertical velocity fluctuations produced near the grid were reduced by the stratification by up to 30 % when U/MN ≈ 0.5. Large-scale internal wave motion was not evident from the observations within about 50 mesh lengths of the grid. The turbulent diffusion from a point source located 4-7 mesh lengths downstream was studied. σy, σz, the horizontal and vertical plume widths, were measured by a rake of probes. σy was found to be largely unaffected by the stratification and grew like t1/2, while σz was found in all cases to reach an asymptotic limit σz∞ where 0.5 ⩽ σZ∞N/w′s ⩽ 2, w′s being the r.m.s. velocity fluctuations at the source; the time taken for σz to reach its maximum was about 2N-1. These results are largely in agreement with the theoretical models of Csanady (1964) and Pearson, Puttock & Hunt (1983). © 1983, Cambridge University Press. All rights reserved.
Print ISSN:
0022-1120
Electronic ISSN:
1469-7645
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
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