Anisotropy in a stratified shear layer

The dynamics and turbulent evolution of a stratified shear layer are explor ed through direct numerical simulation. Turbulence is instigated through th e most unstable asymptotic linear Kelvin-Helmholtz (KH) eigenmode at Richar dson number Ri = 0.05 and Reynolds number Re = 2000 (Ri and Re are defined below). The primary 2D KH vortex succumbs to 3D motions in a manner consist ent with earlier findings. The shear-layer Reynolds number Re-L (defined be low) grows to Re-L approximate to 2.4 x 10(4) as the layer expands and smal l length-scale motions develop. Large- and small-scale anisotropy are exami ned by comparing 1) spectra for the longitudinal and transverse correlation coefficients, 2) RMS velocity components and 3) velocity and temperature d erivatives during the time when turbulence is most intense. The mean shear produces a tendency toward streamwise axisymmetric, as opposed to isotropic , turbulent flow; however, departures from streamwise axisymmetry due to st ratification are evident in the dissipation fields (i.e., at small scales). (C) 2001 Elsevier Science Ltd: All rights reserved.