A Numerical Investigation of Wake Turbulence caused by flow-topography interactions

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Abstract
Ocean currents represent continuous and promising source of hydrokinetic energy. Recent observations along the Kuroshio Current reveal elevated levels of turbulence kinetic energy (TKE), particularly in regions where strong currents interact with sudden topographic features. The Reynolds-averaged Navier–Stokes (RANS) model has been commonly employed to predict current velocities at prospective turbine sites. However, the standard RANS model can introduce significant discrepancies in predicting higher-order turbulence statistics, particularly for turbulence generated by Kelvin–Helmholtz billows. Accurate TKE predictions are critical for assessing hydrokinetic energy potential. This study employs a numerical model with Large Eddy Simulation (LES) to examine wake dynamics and the resulting TKE production/dissipation caused by flow-topography interactions (FTI). The LES model successfully reproduces Kolmogorov's − 5/3 law, indicating that the simulation resolves eddies within the inertial subrange, and the spatial–temporal variations due to breaking internal lee waves. As TKE is elevated in regions of breaking internal lee waves, incorporating ridge geometry is essential for identifying TKE hot spots. Model results under different ambient flow conditions and geometric slopes demonstrate that turbulence characteristics can be effectively predicted using the bifurcation slope, S c (the height of the bifurcation cap versus the corresponding width of the cap). The turbulent characteristics discussed here will be used to evaluate turbulence levels for turbine site assessments.

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