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Low-Reynolds-number oscillating boundary layers on adiabatic slopes

Kaiser, Bryan E. and Pratt, Lawrence J. and Callies, Jörn (2022) Low-Reynolds-number oscillating boundary layers on adiabatic slopes. Journal of Fluid Mechanics, 950 . Art. No. A4. ISSN 0022-1120. doi:10.1017/jfm.2022.794.

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We investigate the instabilities and transition mechanisms of Boussinesq stratified boundary layers on sloping boundaries when subjected to oscillatory body forcing parallel to the slope. We examine idealized forms of boundary layers on hydraulically smooth abyssal slopes in tranquil mid- to low-latitude regions, where low-wavenumber internal tides gently heave isopycnals up and down adiabatic slopes in the absence of mean flows, high-wavenumber internal tides, shelf breaks, resonant tide–bathymetry interactions (critical slopes) and other phenomena associated with turbulence ‘hot spots’. In non-rotating low-Reynolds-number flow, increased stratification on the downslope phase has a relaminarizing effect, while on the upslope phase we find transition-to-turbulence pathways arise from shear production triggered by gravitational instabilities. When rotation is significant (low slope Burger numbers) we find that boundary layer turbulence is sustained throughout the oscillation period, resembling stratified Stokes–Ekman layer turbulence. Simulation results suggest that oscillating boundary layers on smooth slopes at low Reynolds number (Re ⩽ 840), unity Prandtl number and slope Burger numbers greater than unity do not cause significant irreversible turbulent buoyancy flux (mixing), and that flat-bottom dissipation rate models derived from the tide amplitude are accurate within an order of magnitude.

Item Type:Article
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Kaiser, Bryan E.0000-0002-4652-6935
Callies, Jörn0000-0002-6815-1230
Additional Information:The authors thank the Massachusetts Green Computing Center, K. Burns, J. Canfield, R. Ferrari, K. Helfrich, K. Polzin, X. Ruan and A. Thurnherr. This document is approved for Los Alamos Unlimited Release, LA-UR-21-28222. This work was supported by a NSF Graduate Research Fellowship for B.E.K., the Massachusetts Institute of Technology–Woods Hole Oceanographic Institution Joint Program and the National Science Foundation (OCE-1657870).
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NSF Graduate Research FellowshipUNSPECIFIED
Massachusetts Institute of Technology (MIT)UNSPECIFIED
Woods Hole Oceanographic InstitutionUNSPECIFIED
Record Number:CaltechAUTHORS:20221024-123751900.9
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ID Code:117540
Deposited By: Research Services Depository
Deposited On:28 Oct 2022 16:38
Last Modified:01 Nov 2022 17:09

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