A numerical study of the unstratified and stratified Ekman layer

Deusebio E, Brethouwer G, Schlatter P, Lindborg E (2014)

Publication Type: Journal article

Publication year: 2014

Journal

Journal of Fluid Mechanics Cambridge University Press (CUP)

Book Volume: 755

Pages Range: 672-704

DOI: 10.1017/jfm.2014.318

Abstract

We study the turbulent Ekman layer at moderately high Reynolds number, 1600 < Re = δEG/nu < 3000, using direct numerical simulations (DNS). Here, δE = √2v/f is the laminar Ekman layer thickness, G the geostrophic wind, ν the kinematic viscosity and f is the Coriolis parameter. We present results for both neutrally, moderately and strongly stably stratified conditions. For unstratified cases, large-scale roll-like structures extending from the outer region down to the wall are observed. These structures have a clear dominant frequency and could be related to periodic oscillations or instabilities developing near the low-level jet. We discuss the effect of stratification and Re on one-point and two-point statistics. In the strongly stratified Ekman layer we observe stable co-existing large-scale laminar and turbulent patches appearing in the form of inclined bands, similar to other wall-bounded flows. For weaker stratification, continuously sustained turbulence strongly affected by buoyancy is produced. We discuss the scaling of turbulent length scales, height of the Ekman layer, friction velocity, veering angle at the wall and heat flux. The boundary-layer thickness, the friction velocity and the veering angle depend on Lf/uτ, where uτ is the friction velocity and L the Obukhov length scale, whereas the heat fluxes appear to scale with L+=Luτ/ν.

Authors with CRIS profile

Philipp Schlatter

Involved external institutions

University of Cambridge GB United Kingdom (GB) Royal Institute of Technology / Kungliga Tekniska Högskolan (KTH) SE Sweden (SE)

How to cite

APA:

Deusebio, E., Brethouwer, G., Schlatter, P., & Lindborg, E. (2014). A numerical study of the unstratified and stratified Ekman layer. Journal of Fluid Mechanics, 755, 672-704. https://doi.org/10.1017/jfm.2014.318

MLA:

Deusebio, Enrico, et al. "A numerical study of the unstratified and stratified Ekman layer." Journal of Fluid Mechanics 755 (2014): 672-704.

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