THE LARGE-SCALE STABILITY AND SELF-ORGANIZATION IN HOMOGENEOUS TURBULENT SHEAR-FLOW

Large-scale stability of a homogeneous turbulent shear flow UBAR = (Sx 2, 0, 0) is considered. Using a first order smoothing we have obtained the corresponding Reynolds equations. Exploiting the symmetries' prop erty of background flow we are able to obtain a complete set of modes for perturbations of unbounded flow. The flow is rigorously stable to linear disturbances of all wavenumbers. However, the intensive growth of 3-D perturbations at the inviscid stage during the finite times cau sed by non-zero small-scale helicity breaks the validity of the linear approximation. The growth perturbations are elongated along the basic flow. The influence of axial-symmetric helical turbulence on the evol ution of large-scale perturbations of velocity is also under considera tion.