Penetration height and onset of asymmetric behaviour of transitional plane fountains in linearly stratified fluids

The onset of asymmetry, three-dimensionality and entrainment, which occurs in transitional fountains with intermediate Froude and Reynolds numbers (1 < Fr < 10, 10 < Re < 1000) is the key to shed light on the turbulence generation mechanism in fountains. The stratification of the ambient fluid also has significant effects on these characteristics of fountain flows. In this study a series of direct numerical simulation (DNS) are carried out with varied stratifications (quantified by a dimensionless stratification parameter s over 0 ≤ s ≤ 1.5) and different Re over 25 ≤ Re ≤ 300, but all at Fr = 5, to examine the penetration height and the onset of asymmetry in transitional plane fountains. The results show that fountain heights decrease when s increases, but increase when Re increases. When Re is small, a fountain generally starts to show the asymmetric behaviour at a much later time and the extent of asymmetry increases when Re increases, although the rate of increase decreases with Re. On the other hand, the stratification of the ambient fluid is found to play a positive role to stabilize the flow and to alleviate its asymmetric and unsteady behavior.

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AFMC 2014: 19th Australasian Fluid Mechanics Conference

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978-0-646-59695-2

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