Grid-Free Simulation of the Spatially Growing Turbulent Mixing Layer

摘要

The spatially developing, unforced, turbulent mixing layer is simulated via a grid-free vortex method. Vortex filaments composed of straight tubes are used as the computational element with new vortex tubes produced as the filaments stretch. A loop removal algorithm serves as a de facto subgrid model limiting growth in the number of elements to practical levels. The computations are high resolution and well resolve the mixing layer from its unforced inception as a laminar flow through transition to a self-similar turbulent state. Mean velocity statistics including growth rate and Reynolds stresses agree well with experimental values. The vortical composition of the transition region is found to develop in one or another of the modes that have been documented in previous experiments and computations: roller/rib vortices, the chain-link fence structure in a diamond shaped pattern, and somewhat oblique roller/rib configuration with partial pairing. Evidently, small perturbative effects that are intrinsic to the numerical scheme influence which transitional mode appears locally in the simulations. The computations offer a clear view of the downstream dissolution of the identifiable structure into turbulence in the late transition and the salient aspects of the process are noted.