| dc.description.abstract | This report examines the postulate of local isotropy in stratified homogeneous turbulence from a theoretical point of
view. The study is based on a priori analysis of the evolution equations governing single-point turbulence statistics that
are formally consistent with the Navier-Stokes equations. The Boussinesq approximation has been utilized to account
for the effect of buoyancy – a simplifying assumption that constitutes an excellent approximation in the case considered
here. The study concludes that the hypothesis of local isotropy is formally inconsistent with the Navier-Stokes equations
in homogeneous stratified turbulence. An estimate is provided that suggests that local isotropy may constitute only a
physically justifiable approximation in the limit of a clear-cut separation between the time scales associated with the
imposed buoyancy and the turbulent eddy-turnover time scale. This is unlikely to happen in most flows, at least those
not too far from equilibrium. The results also suggest that the dynamical dependence of the small-scale turbulence on
large-scale anisotropies associated with imposed density stratification is significantly stronger than that caused by an
imposed mean straining. This report has in a revised form been published in SIAM Journal of Applied Mathematics,
2003, Vol. 64, No. 1, pp. 309-321. | en_GB |