7 research outputs found
Elliptic instability in the Lagrangian-averaged Euler-Boussinesq-alpha equations
We examine the effects of turbulence on elliptic instability of rotating
stratified incompressible flows, in the context of the Lagragian-averaged
Euler-Boussinesq-alpha, or \laeba, model of turbulence. We find that the \laeba
model alters the instability in a variety of ways for fixed Rossby number and
Brunt-V\"ais\"al\"a frequency. First, it alters the location of the instability
domains in the parameter plane, where is the
angle of incidence the Kelvin wave makes with the axis of rotation and
is the eccentricity of the elliptic flow, as well as the size of the associated
Lyapunov exponent. Second, the model shrinks the width of one instability band
while simultaneously increasing another. Third, the model introduces bands of
unstable eccentric flows when the Kelvin wave is two-dimensional. We introduce
two similarity variables--one is a ratio of the Brunt-V\"ais\"al\"a frequency
to the model parameter , and the other is the
ratio of the adjusted inverse Rossby number to the same model parameter. Here,
is the turbulence correlation length, and is the Kelvin wave
number. We show that by adjusting the Rossby number and Brunt-V\"ais\"al\"a
frequency so that the similarity variables remain constant for a given value of
, turbulence has little effect on elliptic instability for small
eccentricities . For moderate and large eccentricities,
however, we see drastic changes of the unstable Arnold tongues due to the
\laeba model.Comment: 23 pages (sigle spaced w/figure at the end), 9 figures--coarse
quality, accepted by Phys. Fluid
Euler-Poincare formulation and elliptic instability for nth-gradient fluids
The energy of an gradient fluid depends on its Eulerian velocity
gradients of order . A variational principle is introduced for the dynamics
of gradient fluids and their properties are reviewed in the context of
Noether's theorem. The stability properties of Craik-Criminale solutions for
first and second gradient fluids are examined.Comment: 17 pages, 5 figures (low quality), each in several part