Laboratory and numerical experiments on the near wake of a sphere in a stably stratified ambient

Abstract

The flow around and behind a sphere in a linear density gradient has served as a model problem for both body-generated wakes in atmospheres and oceans, and as a means of generating a patch of turbulence that then decays in a stratified ambient. Here, experiments and numerical simulations are conducted for 20 values of Reynolds number, $Re$ , and internal Froude number, $Fr$ , where each is varied independently. In all cases, the early wake is affected by the background density gradient, notably in the form of the body-generated lee waves. Mean and fluctuating quantities do not reach similar states, and their subsequent evolution would not be collapsible under any universal scaling. There are five distinguishable flow regimes, which mostly overlap with previous literature based on qualitative visualisations and, in this parameter space, they maintain their distinguishing features up to and including buoyancy times of 20. The possible relation of the low $\{Re, Fr\}$ flows to their higher $\{Re, Fr\}$ counterparts is discussed.

Discrete and Continuous Symmetries of Stratified Flows Past a Sphere

“…Moreover, the results agree with measurements [37][38][39][40]. Additional simplifications, including the assumption of the absence of diffusion κ S = 0 [41] or the equality of dissipative coefficients of kinematic viscosity and diffusivity Sc = ν/κ S = 1 [42], are made when constructing the numerical solutions of a complex multiscale system (1).…”

“…Analytical [87], numerical [88][89][90][91], and experimental studies [41,42] of the internal wave field and the generally round turbulent wake behind a rapidly moving sphere in a CSF are being actively pursued using various approaches.…”