Quantification of mixing efficiency, Rif, in stratified-shear flows has been an interesting debate in the environmental fluid dynamics community. A value of Rif = 0.17, first proposed by Osborn (1980), has been widely used in oceanographic applications to model the eddy diffusivities in global models. However, there are limitations with the universality of Rif, especially in certain regimes.
We perform high-resolution experiments in a most common variant of stratified-shear flow, namely, gravity currents to probe into the energetics and associated turbulence and mixing for a range of initial conditions. Simultaneous PIV-PLIF measurements are done to obtain the local statistics of density and velocity.
Some interesting finding includes the effect of countergradient fluxes in quantification of Rif and its non-universality in buoyancy-dominated regimes. Owing to ambiguities in parametrizing Rif as a function of a single flow parameter, like buoyancy Reynolds number (Reb) or gradient Richardson number (Rig), a multiparameter space is considered using turbulent Froude number, FrK, and turbulent Reynolds number, ReL.
New insights are achieved, wherein it is observed that for a given Reb/Rig, Rif can assume different values owing to regimes set up by Frk, ReL and even Prandtl number, Pr. If time permits, I will also briefly touch upon the energetics of a forced plume evolving in a linearly stratified environment.
Sridhar Balasubramanian is presently a professor in the Department of Mechanical Engineering and an adjunct faculty in IDP Climate Studies at the Indian Institute of Technology Bombay (widely known as IIT Bombay).
He received his Ph.D. from Arizona State University and was a postdoctoral fellow at Los Alamos National Lab before joining IIT Bombay in 2012. His research interests are in stratified-shear flows, buoyant jets and plumes, convection, particle-bearing flows, and ocean modeling. His team at IIT Bombay has developed Geophysical and Multiphase Flows Laboratory with state-of-the-art diagnostics for probing small-scale dynamics in fluid flows.