Characteristics of the surface signatures induced by a sphere in a linearly stratified flow

Abstract

Internal waves generated by a moving body submerged in a stratified fluid typically yield modest surface signatures. Large-eddy simulation (LES) is employed to capture the surface signatures generated using a moving sphere in a linearly stratified fluid with various Froude numbers (Fr) and diving depths (D). For surface Kelvin wakes, with increasing Froude numbers (Fr), the wake angle (θ) decreases, the wavelength (L) and the maximum surface wave amplitude (Amax) increases. Within the range of our simulation, the influence of diving depth (D) on wake angle (θ) and wavelength (L) is insignificant, while the maximum surface wave amplitude (Amax) decreases as diving depth (D) increases. Additionally, surface turbulent signatures characterised by horizontal divergence (divh) are identified in the near wake. The results demonstrated the following: the horizontal divergence (divh) is transported upstream and downstream from internal wakes to the free surface, whereas the vertical vorticity (ωy) is only transported downstream. And the horizontal divergence (divh) can be transmitted for a larger distance than the vertical vorticity (ωy).