DNS

DNS solves turbulence without any turbulence model. There are two requirements that a DNS must meet if it is to represent a turbulent flow. First, all scales of motion need to be captured, in the deterministic sense, by the size of the grid, which must be no larger than the smallest length scale, called the Kolmogorov scale, η. Second, all the significant fluid motions allowed by the Navier-Stokes equations have to be captured. The domain of the calculation must be at least as large as either the physical domain or the largest turbulent eddy. A useful measure of this scale is the integral scale of the turbulence which is the distance over which the fluctuating velocity remains correlated. At lease one integral scale is needed in the calculation domain, typically three integral scales are needed. DNS has faced essential diffculties.