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Statistics of surface flow structures on decaying grid turbulence

 

作者: S. Loewen,   B. Ahlborn,   A. B. Filuk,  

 

期刊: Physics of Fluids(00319171)  (AIP Available online 1986)
卷期: Volume 29, issue 8  

页码: 2388-2397

 

ISSN:0031-9171

 

年代: 1986

 

DOI:10.1063/1.865532

 

出版商: AIP

 

数据来源: AIP

 

摘要:

The surface flow pattern of decaying turbulence generated by a vertical bar grid in a towing tank has been studied. The velocities and positions of about 2×104Al aluminum filing tracers following the surface motion have been measured and statistically analyzed. From ten photo series, each of 10 mesh width span and 40 mesh widths long, 2000 surface eddies were identified and studied. The flow field is decomposed into ‘‘closed’’ rotating flow structures (the surface eddies) and ‘‘open’’ flow structures (rivers) of predominantly translational motion. There are also relatively stagnant areas that grow in number and size with time. Immediately behind the grid the average energy densities of the surface eddieseeand the riverserare about equal buteedecays at a greater rate thaner. The eddy size distribution gradually shifts to larger eddies and an increasing fraction of the fluctuating kinetic energy is transferred into the rivers. In the collision‐dominated equilibrium region, the eddy and the river energy distributions can be described by Boltzmann‐type functions. These distributions may then be characterized by ‘‘temperature’’ &thgr;eand &thgr;rfor eddies and rivers. These temperatures decay steadily throughout the observation period, but remain approximately equal to each other. The relationship between the surface flow dynamics and the subsurface and bulk turbulent grid‐flow is examined.

 

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