Penetration Height and Onset of Asymmetric Behaviour of Transitional Plane Fountains in Linearly Stratified Fluids

摘要

The onset of asymmetry, three-dimensionality and entrainment,which occurs in transitional fountains with intermediate Froudeand Reynolds numbers (1 < Fr < 10, 10 < Re < 1000) is the keyto shed light on the turbulence generation mechanism infountains. The stratification of the ambient fluid also hassignificant effects on these characteristics of fountain flows. Inthis study a series of direct numerical simulation (DNS) arecarried out with varied stratifications (quantified by adimensionless stratification parameter s over 0 ≤ s≤ 1.5) anddifferent Re over 25 ≤ Re ≤300, but all at Fr = 5, to examine thepenetration height and the onset of asymmetry in transitionalplane fountains. The results show that fountain heights decreasewhen s increases, but increase when Re increases. When Re issmall, a fountain generally starts to show the asymmetricbehaviour at a much later time and the extent of asymmetryincreases when Re increases, although the rate of increasedecreases with Re. On the other hand, the stratification of theambient fluid is found to play a positive role to stabilize the flowand to alleviate its asymmetric and unsteady behavior.