Transcript Document

The Environmental Fluid Dynamics Lecture Series
Presents a Seminar
Dr. Karan Venayagamoorthy
Associate Professor
Civil & Environmental Engineering
Borland Professor
Colorado State University
Tuesday, February 4
Dean’s Boardroom, 258 Fitzpatrick
11am-12noon
A UNIFYING FRAMEWORK FOR PARAMETERIZING STABLY
STRATIFIED SHEAR-FLOW TURBULENCE
ABSTRACT
An alternative framework for parameterizing stably stratified shear-flow turbulence is
presented. Using dimensional analysis, four non-dimensional parameters of interest are
identified that consider the independent effects of stratification, shear, viscosity, and scalar
diffusivity. In the interest of geophysical applications, the problem is further simplified by
considering only high Reynolds number flow. This leads to a two-dimensional parameter
space based on a buoyancy strength parameter (i.e. an inverse Froude number) and a shear
strength parameter. Consideration for the gradient Richardson number allows the space to
be divided into an unforced regime, a shear-dominated regime, and a buoyancy-dominated
regime. On this basis, a large database of direct numerical simulation and laboratory data
from various sources is evaluated. Of particular interest is the observed length scale of
overturning. Overturns are found to scale with k1/2/N in the buoyancy-dominated regime,
k1/2/S in the shear-dominated regime, and k3/2/ϵ in the unforced regime, where k, N, S,
and ϵ are the turbulent kinetic energy, buoyancy frequency, mean shear rate, and turbulent
dissipation rate, respectively. Implications for estimates of diapycnal mixing in the ocean
are discussed and a new parameterization for eddy diffusivity is presented.