Investigation of plane mixing layer using large eddy simulation

Spatially evolving turbulent mixing layers are investigated in this paper using large eddy simulation. The evolutions of large vortex structures are obtained, in which the processes of vortex roll up, growth, pairing and breaking up are shown in details. The simulated flow patterns agree well with experimental visualization results. Predicted results of mean properties of streamwise velocity, fluctuating velocity and Reynolds stress at different sections show good self-similarity and agree well with experimental measurements. Linear growth of the momentum thickness along the streamwise direction is then obtained, indicating that pairing and amalgamating of large vortex structures in plane mixing layers occur randomly in space and time. The effects of convection velocity and the rate of shear on the evolution of vortex structures, self-similarity as well as momentum thickness are also investigated. The rate of shear has a significant effect on the evolution of coherent structure and the slope of momentum thickness growth, while the convection velocity only affects the space interval of the adjoining vortices. The rate of shear and convection velocity have no significant effect on the non-dimensional distributions of turbulence statistics. Self-similarities are therefore obtained for different rates of shear and convection velocities.