BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:Quantifying mixing in simulations of stratified flows - Chris Howl
 and\, University of Twente\, Netherlands
DTSTART:20210528T150000Z
DTEND:20210528T160000Z
UID:TALK160483@talks.cam.ac.uk
CONTACT:virginia mullins
DESCRIPTION:Turbulent mixing exerts a significant influence on many physic
 al processes in the ocean. In a stably stratified Boussinesq fluid\, this 
 irreversible mixing describes the conversion of available potential energy
  (APE) to background potential energy (BPE). In some settings the APE fram
 ework is difficult to apply and approximate measures are used to estimate 
 irreversible mixing. For example\, numerical simulations of stratified tur
 bulence often use triply periodic domains to increase computational effici
 ency. In this set-up\, however\, BPE is not uniquely defined and the metho
 d of Winters et al. (J. Fluid Mech.\, vol. 289\, 1995\, pp. 115–128) can
 not be directly applied to calculate the APE. We propose a new technique t
 o calculate APE in periodic domains with a mean stratification. By definin
 g a control volume bounded by surfaces of constant buoyancy\, we can const
 ruct an appropriate background buoyancy profile b∗(z\,t) and accurately 
 quantify diapycnal mixing in such systems. This technique also permits the
  accurate calculation of a finite-amplitude local APE density in periodic 
 domains. The evolution of APE is analysed in various turbulent stratified 
 flow simulations. We show that the mean dissipation rate of buoyancy varia
 nce χ provides a good approximation to the mean diapycnal mixing rate\, e
 ven in flows with significant variations in local stratification. We discu
 ss how best to interpret these results in the context of quantifying diapy
 cnal diffusivity in real oceanographic flows. 
LOCATION:GKB 100 Fluid Mechanics Webinar Series
END:VEVENT
END:VCALENDAR