School of Mechanical Engineering Prof Jan-Bert Flor

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SCHOOL OF MECHANICAL ENGINEERING SEMINAR
Monday, October 28, 2019 at 14:00
Wolfson Building of Mechanical Engineering, Room 206

Internal waves and wave focusing in stratified and/or rotating fluids

Dr. Jan-Bert Flor, LEGI, CNRS

In this presentation I will discuss experimental results on the generation ofl internal waves, in rotating and/or stratified fluids, that are investigated in the context of internal wave generation in the ocean.  Internal waves were generally investigated in two-dimensional flow geometries. How does the wave field change in a three dimensional flow geometry ? After a general introduction omn former results, the wave field such as generated by a horizontally oscillating torus will be discussed. This wave field has the form of a cone below and above the torus, with a focal point in the apex where the waves reach a maximum amplitude. After considering the basic properties of this wave field and a comparison with an approximate linear theory, we consider its nonlinear aspects  for different amplitudes of oscillations. Above a certain threshold, wave breaking appears, and coincides with resonant wave triads appearing near the focal region (Ermanyuk, Shmakova & Flór, J Fluid Mech 2017; Shmakova & Flór, J. Fluid Mech 2019). Next we discuss the flow induced by the oscillation of a vertically oscillating torus in a rotating fluid, and the formation of an isolated blob of turbulence in the focal point. The turbulent blob in the rotating fluid leads to the formation of an organised columnar vortex (Duran Matute et al 2013, Phys. Rev. E 87;  Flór et al . in prep.), whereas the overturning waves in a stratified fluid hardly organise into a large scale motion. Finally we’ll discuss the differences in dynamics when stratification and rotation are present.