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SELF-PROPELLED WAKES AT DIFFERENT FROUDE NUMBERS IN A STRATIFIED FLUID

Matthew B. de Stadler
Mechanical and Aerospace Engineering Department University of California San Diego 9500 Gilman Drive #0411, La Jolla, CA 92093

Sutanu Sarkar
Mechanical and Aerospace Engineering Department University of California San Diego 9500 Gilman Drive #0411, La Jolla, CA 92093

Abstract

Direct numerical simulation is used to study the evolution of a self-propelled, temporally evolving, wake in a stratified fluid at three different Froude numbers: 3, 10, 20. At higher Froude number the wake was found to decay faster resulting in decreased values of mean and turbulent statistics such as the defect velocity, mean kinetic energy, turbulent kinetic energy, and turbulence intensities, and increased wake dimensions at equivalent Nt, where N is the buoyancy frequency. Despite large quantitative differences between cases, transition between flow regimes was found to occur at comparable Nt. A significant increase in both the relative contribution and absolute value of the cross-stream component of the mean kinetic energy was observed as a result of the collapse in the vertical direction from 3 < Nt < 30 in the higher Froude number cases. Different scaling was observed for mean and turbulent statistics which shows that self-similarity is not valid. Consistent mean velocity and vertical vorticity structure were observed between cases despite significant differences in turbulent kinetic energy structure.