Postgraduate Fluid Mechanics Seminars Spring 2020
These seminars (unless otherwise stated) will take place on Wednesdays at 4pm in room 706 on a bi-weekly basis - see the map for further details.
05 February 2020
NO SEMINAR
19 February 2020
NO SEMINAR
04 March 2020
Speaker: Leo Middleton (University of Cambridge)
Title: A general criterion for the release of background potential energy by double diffusion
Abstract:
Double diffusion occurs when the fluid density depends on two components that diffuse at different rates (e.g. heat and salt in the ocean). Double diffusion can lead to an up-gradient buoyancy flux and drive motion at the expense of potential energy. Here, we follow the work of Lorenz (1955); Winters et al. (1995) for a single component fluid and define the ‘background’ potential energy (BPE) as the energy associated with an adiabatically sorted density field and derive its budget for a double-diffusive fluid. We find that double diffusion can convert BPE into ‘available’ potential energy (APE), unlike in a single-component fluid where the transfer of APE to BPE is irreversible. We derive a simple criterion for an up-gradient flux in terms of local temperature and salinity gradients, generalising previous 1D results to a 3D field. The criterion we develop for a release of BPE can be used to analyze the energetics of mixing and double diffusion in the ocean and other multiple component fluids. We illustrate its application by briefly discussing how we have applied it to the ice shelf-ocean boundary layer.