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- Title
Determination of the entrainment coefficient of a pure plume using the salt-bath technique.
- Authors
Liu, Yang; Li, Xiaoqing; Huang, Lan; Liu, Zuwen
- Abstract
The entrainment coefficient of the pure plume, the ratio of the radial velocity of the entraining fluid at the edge of the plume to the axial velocity, is characterized by a remarkable deviation from the actual value in references. To a turbulent flow with Gaussian profiles, the entrainment coefficient is accepted in a considerably wide range from 0.07 to 0.11 for pure plumes. In this study, the entrainment coefficient of a pure plume is determined by analyzing the stratified interface formed between fresh water and a buoyant fluid in a confined space. The interface position is determined using digital image processing while conducting salt-water experiments. The displacement of the virtual origin of the real plume is added to the original heights of the confined space and stratified interface because the plume in the laboratory is from a source of finite area rather than from a point. The two virtual source position determination methods are compared; the one where the ratio of the displacement of the virtual origin to the nozzle diameter is related only to the source parameter Γ is selected for the theoretical analysis. The experimental data of the source parameter Γ and corresponding entrainment coefficients indicate that the α value of the pure plume is 0.09251 when using the interpolation method. This value is validated through displacement experiments on a pure plume created by supplying salt water through the nozzle in a laboratory. Further, the entrainment coefficient of a turbulent jet is determined based on the stratified interface behavior in a confined space; the experimental results support the speculation that the entrainment coefficient of the pure jet should be 0.057. The experimental data of the entrainment coefficient α plotted against parameter Γ in the available literature are compared with those estimated from semi-empirical equations with two asymptotic values suggested in this paper. Article Highlights: Entrainment coefficient of a pure plume is determined by analyzing the interface between fresh water and buoyant fluid. The interface position is determined using digital image processing while conducting salt-water experiments. Two virtual source position determination methods are compared. The α value of the pure plume is determined to be 0.09251 when using the interpolation method. Experimental results support the speculation that the entrainment coefficient of the pure jet should be 0.057
- Subjects
DIGITAL image processing; TURBULENT jets (Fluid dynamics); FRESH water; TURBULENT flow; TURBULENCE; VOLCANIC plumes; MARKOV spectrum
- Publication
Environmental Fluid Mechanics, 2021, Vol 21, Issue 6, p1303
- ISSN
1567-7419
- Publication type
Article
- DOI
10.1007/s10652-021-09824-3