Self-similar states in turbulent mixing layers (Q2770288)

The paper focuses on the study of self-similar states in turbulent mixing layers that form between two fluid streams moving with different velocities. The first part gives the motivation of continuous effort made in this direction, which is not only the technological importance of these flows, but also the rather large disparity in the results. In the second part the governing equations are described together with the simulation method and parameters. The governing equations for LES of turbulent mixing layers are incompressible filtered Navier-Stokes equations, which describe the evolution of large scales. All quantities are made dimensionless by the velocity difference between the high- and low-speed sides of the layer and by its momentum thickness at the initial time, \(\theta_0\). The term which must be modelled is the subgrid scale stress term \(\tau_{ij}\). This one is parametrized using a dynamic eddy-viscosity model. The Navier-Stokes governing equations are integrated in time using Adams-Bashforth fractional-step method. Both advective and diffusive terms are treated explicitly. Periodic boundary conditions are applied in homogeneous streamwise and spanwise directions. At the open boundaries in the cross-stream direction radiative boundary conditions are used, which allow the flow to enter or exit the computational domain without influencing the solution in the domain near the open boundary. In order to examine the effect of initial conditions on the evolution of the layer and also to determine which dimension of computational domain has the largest effect on the layer evolution, a series of six computations is carried out.NEWLINENEWLINE The third section contains the main results obtained performing large eddy simulations of temporally evolving turbulent mixing layers. One presents the validation of the numerical algorithm and the subgrid-stress model. The authors also show a grid refinement study. Then, by a discussion of the topology of the flow, they present the turbulent statistics which is significantly affected both by the initial conditions and by the computational domain size.NEWLINENEWLINE The last section presents some concluding remarks concerning the significance of the above results. Thus, in all six cases of simulation of mixing layers evolved into self-similar slates, it is found that the initial conditions and the size of flow domain influence the shape of coherent eddies of the flow and its statistics.