No abstract

No abstract

This article considers one of the simplest shear flows-ID time-dependent plane mixing layer. Under certain conditions, many more complicated flows are similar to it: timeindependent plane mixing layer, initial portion of plane and round jets, initial mixing phase in cylindrical vortex, etc. This application was previously studied in a 2D approximation. In this computation the turbulence was treated as the result of random perturbations initially applied to the interface of two flows. Numerical simulation used a 2D EGAK code. The computational results were interpreted using the version of semi-empirical turbulent theory with isotropic Reynolds tensor (model 1). This article continues the studies by Bakhrakh; in addition, a similar approach is implemented based on 3D simulation with the TREK method. The data interpretation uses the version of semi-empirical theory with and without Reynolds tensor anisotropy (models 1 and 2, respectively). Computational setupThe setup is similar to that from Bakhrakh et al. (1983): initially two half-spaces separated by the plane are filled with perfect gases (y = 1.4) with densities p t = 0.001 and p 2 > rtpi for the same pressures P o =\. The gas in region 1 moves with the velocity w 0 = dy/dt = 4 parallel to the interface, one in region 2 is at rest.Initially, the random perturbations v = dz/dt = ±0.1 w o of the velocity component normal to the interface are applied to the latter. The computational domain is a cube with the side A = 7.5 and the number of cells N r x Ni x Ni. For the outer domain boundaries normal to the separate plate, the periodicity condition was specified with the period A; the rigid wall was applied to other boundaries.These 3D computations were run where n = p 2 /pi and the number of cells N! varied (see table 1). In addition, two 2D computations were run on a 45 x 45 grid, one of these, like in the 3D case, using the approximation of motion equation with the second-order approximation over spatial variables and the other using the first-order approximation. The setup is similar to the 3D case; the longitudinal coordinate is x, the transversal coordinate is y.Note that the incompressibility condition was approximately met because of the relation Wo « Wo/Poy where p o -min(p 1) p 2 )- Computational resultsThe flow evolution observed in computations 1 and 2 (p, = p 2 ) is similar to that from Bakhrakh et al. (1983). The vortices grow with time (see figures 1 and 2) showing, for the computation 1, the isolines of volume concentrations /? = 0.5 in the plane y = 0.25 and x = 0.25 normal to the interface and the linear variation law is achieved for the turbulent mixing zone (TMZ) width L(t) (figure 3). Here L was defined as the width of the self-similar

No abstract

No abstract