2023/10/30 by Andrés Posada‐Bedoya, Posada-Bedoya, Andres, Jason Olsthoorn +3
Earth and Planetary Sciences · #Atmospheric and Oceanic Physics (physics.ao-ph) #Coastal and Marine Dynamics #FOS: Physical sciences #Fluid Dynamics (physics.flu-dyn) #Ocean Waves and Remote Sensing #Oceanographic and Atmospheric Processes
paper · pdf · doi:10.48550/arxiv.2310.19971
openalex publication_date 2023/10/30 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We investigated the stability of the bottom boundary layer (BBL) beneath periodic internal solitary waves (ISWs) of depression over a flat bottom through two-dimensional direct numerical simulations. We explored the effects of variation in wave Reynolds number ReISW and wave period on the nature of the instability, and energy production in the separated BBL. The instability characteristics and rate of vortex shedding of the BBL were strongly dependent on ReISW. The BBL was laminar and convectively unstable at ReISW 90 and 300, respectively. At ReISW=300, the convective wave packet was periodically amplified by each successive ISW, until vortex-shedding occurred. This implies noise-amplification behavior and suggests that the discrepancies in the critical ReISW, for vortex shedding between lab and different numerical simulations, are due to differences in background seed noise. Instability energy decreased under the front shoulder of the ISW, analogous to flow relaminarization under a favourable pressure gradient. At larger ReISW=900, the BBL was initially convectively unstable, and then the instability tracked with the ISW, characteristic of global instability, regardless of the ISW periodicity. The simulated initial convective instability at both ReISW 300 and 900 is in agreement with local linear stability analysis which predicts that the instability group speed is always lower than the ISW celerity. Increased free-stream perturbations and larger ReISW shift the location of vortex shedding (and enhanced bed shear stress) closer to the ISW trough, thereby potentially changing the location of maximum sediment resuspension from the ISW, in agreement with field observations at higher ReISW.