Direct numerical simulation of salt sheets and turbulence in a double-diffusive shear layer
نویسندگان
چکیده
[1] We describe three-dimensional direct numerical simulations (DNS) of double-diffusively stratified flow interacting with inflectional shear. The extreme difference in diffusivity (and thus minimum length scale) between heat, salt and momentum in seawater is replicated for the first time in a three-dimensional simulation. The primary instability generates salt sheets, which are oriented parallel to the direction of the sheared background flow. Subsequently, two distinct mechanisms of secondary instability combine to lead the flow to a turbulent state. In this state, the effective saline diffusivity is smaller than that calculated by previous investigators for the unsheared case. The Schmidt number is much smaller than unity, indicating that salt sheets are less effective at transporting momentum than is often assumed. Citation: Kimura, S., and W. Smyth (2007), Direct numerical simulation of salt sheets and turbulence in a double-diffusive shear layer, Geophys. Res. Lett., 34, L21610, doi:10.1029/2007GL031935.
منابع مشابه
Interaction of Kelvin-Helmholtz and salt sheet instabilities in a sheared, fingering-unstable layer
Motivated by observations of thermohaline staircases in the midlatitude oceans, we have conducted direct numerical simulations (DNS) of the evolution of a diffusively unstable shear layer. This flow supports both KH and salt sheet instabilities, and we wish to see how the two mechanisms work together to drive the transition to turbulence. The main controlling parameters are the bulk Richardson ...
متن کاملTurbulence in a sheared , salt - fingering - favorable environment : 1 Anisotropy and effective diffusivities
5 Direct numerical simulations (DNS) of a shear layer with salt-fingering-favorable stratifica6 tion have been performed for different Richardson numbers Ri and density ratios Rρ. When 7 the Richardson number is infinite (unsheared case), the primary instability is square plan8 form salt-fingering, alternating cells of rising and sinking fluid. In the presence of shear, 9 salt-fingering takes t...
متن کاملTurbulence in a Sheared, Salt-Fingering-Favorable Environment: Anisotropy and Effective Diffusivities
Direct numerical simulations (DNS) of a shear layer with salt-fingering-favorable stratification have been performed for different Richardson numbers Ri and density ratios Rr. In the absence of shear (Ri 5 ‘), the primary instability is square planform salt fingering, alternating cells of rising and sinking fluid. In the presence of shear, salt fingering takes the form of salt sheets, planar re...
متن کاملNumerical Simulation of Separation Bubble on Elliptic Cylinders Using Three-equation k-? Turbulence Model
Occurrence of laminar separation bubbles on solid walls of an elliptic cylinder has been simulated using a recently developed transitional model for boundary layer flows. Computational method is based on the solution of the Reynolds averaged Navier-Stokes (RANS) equations and the eddy-viscosity concept. Transitional model tries to simulate streamwise fluctuations, induced by freestream turbulen...
متن کاملSecondary instability of salt sheets
In the presence of a vertically varying horizontal current (background shear), the salt-fingering instability is supplanted by the salt-sheet instability. Previous direct numerical simulation (DNS) experiments on salt sheets revealed that flow becomes turbulent via secondary instabilities. We call these instabilities zig-zag and tip modes. Here, we investigate the physics of these modes using l...
متن کامل