The Downstream of a Density-Stratified Sphere Wake


  • Karu Chongsiripinyo Chulalongkorn University



Wakes, Stratification, Environmental fluid dynamics, Computational fluid dynamics


The objective of the present work is to access moderately-stratified wake statistics into the far downstream. This is accomplished via a continuation of the solution from the stratified-wake, body-inclusive, large-eddy simulation of Chongsiripinyo & Sarkar (TSFP10) by a temporal-model, direct numerical simulation. Simulation of stratified wake at Re = U∞D/ν = 10^4 and Fr = U∞/ND = 3 is performed; U∞, D, and N are sphere velocity, sphere diameter, and buoyancy frequency. Three findings are as follows. 1) In the late-NEQ regime, centerline mean streamwise velocity deficit continues to decay with the power-law exponent U0 ∝ t^{−0.4} and while the progression of horizontal wake span is at LH ∝ t^{1/3}, vertical wake extent remains stagnant (LV ∝ t^0). 2) The beginning of NEQ-Q2D transitioning is found to be where the mean wake is geometrically most anisotropic, that is the ratio LV /LH is at a minimum. The transitioning is a gradual process that lasts 50 ≤ N t ≤ 250. 3) In the Q2D regime, vertical profile of the mean streamwise defect velocity (Ud) exhibits self-similarity. This self-similar state is not of Gaussian-type but better fitted with individual plane-wake self-similarity solution. The centerline defect velocity rapidly decays at a rate U0 ∝ t^{−3/4}. Horizontal extension growth rate is reduced to be LH ∝ t^{1/4} and the exponential growth rate of wake height is found to be LV ∝ t^{1/2}, an indication of the dominating viscous diffusion process.


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Author Biography

Karu Chongsiripinyo

Department of Mechanical Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok
10330, Thailand


Published In
Vol 25 No 5, May 31, 2021
How to Cite
K. Chongsiripinyo, “The Downstream of a Density-Stratified Sphere Wake”, Eng. J., vol. 25, no. 5, pp. 1-12, May 2021.