Computing Turbulent Shear Flows — A Convenient Conspiracy

Physical and computational factors are considered that help make simulations of turbulent flow practical despite the wide range of scales involved. The first two factors relate to the behavior of the spectrum of the kinetic energy as a function of the size of the flow structures in the system (the wavelength). As the wavelength decreases, this spectrum drops off so quickly that the shortest scale lengths do not contain very much of the energy of the flow. A third factor is that there are really very few features of the flow that are important at scales approaching the Kolmogorov length or even ten times larger. The final observation concerns the numerical properties of a class of fluid-dynamic algorithms called nonlinear monotone methods. Because these methods properly connect the flow at the smaller unresolved scales, the solution is reliable down to the smallest resolved scales of the calculation. (AIAA)