Final Report on Project GGT0607: Lattice Boltzmann Direct Numerical Simulations of Grid-Generated Turbulence

The largest known direct numerical simulations of grid-generated turbulence were performed, on one hand resolving the grid placed in an incompressible fluid flow while on the other hand following reliably the evolution of flow structure both in the direction of the mean flow and across it well into a region of self-similar behaviour. The excellent scaling of the employed lattice Boltzmann algorithm allowed to perform a series of DNS runs and quantify several parametric effects. Several major qualitaitve results were obtained, as well, having immediate impact on turbulence modeling: A new algebraic law (of Kolmogorv type) was discovered for the decay of turbulent kinetic energy in low-intensity grid-generated turbulence. Furthermore, the assumption of the existence of a single decay rate for the anisotropy of weak “homogeneous” turbulence was shown to be qualitatively inappropriate, while the assumption of an “inertial range” for the spatial development of such turbulence – on which the former assumption should be based – appears to be valid.