Numerical reproduction of unsteady small-scale eddy structures in the deep ocean

Unsteady small-scale deep ocean eddies were reproduced by a combination of the wavelet transform of measured data and a turbulent forcing technique in CFD. First, we measured time-sequential velocity data at the depth of 2000 m in the ocean, about 500 km offshore of Okinawa Island. Four 3D velocimeters were allocated in a form of a tetrahedron, the edge length of which is 2.5 m. The wavelet transform was applied to reproduce unsteady spatial flow structures from the 4 sets of information in the time domain. The directional spectra of time-dependent large-scale eddies were analysed by 3 sets of cross spectra obtained by the wavelet transform. Second, we conducted a large eddy simulation in CFD by forcing the large-scale eddies in a cubic computational domain, the edge length of which is 30 m, to generate small-scale ocean turbulence. The frequency spectrum of the reproduced high-wavenumber flow was compared well with that of the measurement.